Biotechnology

Biotechnology

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Board Coverage AQA Paper 2 | Edexcel A Paper 2 | OCR (A) Paper 2 | CIE Paper 4

1. Recombinant DNA Technology

1.1 Overview

Recombinant DNA technology involves combining DNA from different sources to create new, artificial DNA molecules that can be introduced into host organisms. This is the basis of genetic engineering and genetic modification (GM).

1.2 Tools of Recombinant DNA Technology

Restriction endonucleases (restriction enzymes) cut DNA at specific recognition sequences. These sequences are typically 4--8 base pairs long and palindromic (the sequence reads the same on both strands in the 5' to 3' direction).

Enzyme	Recognition Sequence	Cut Type	Sticky Ends
EcoRI	5'-GAATTC-3'	Staggered	AATT
BamHI	5'-GGATCC-3'	Staggered	GATC
HindIII	5'-AAGCTT-3'	Staggered	AGCT
SmaI	5'-CCCGGG-3'	Blunt	None

Staggered cuts produce sticky ends (single-stranded overhangs) that are complementary and can base-pair with any DNA cut with the same enzyme. Blunt cuts produce flat ends that can be joined to any other blunt-ended DNA.

DNA ligase joins DNA fragments by catalysing the formation of phosphodiester bonds between the $3'$-OH of one fragment and the $5'$-phosphate of another. T4 DNA ligase can join both sticky-end and blunt-end fragments.

Vectors are DNA molecules used to carry foreign DNA into host cells:

Vector Type	Capacity	Advantages	Disadvantages
Plasmid	$< 10\ \mathrm{kb}$	Easy to manipulate; high copy number	Limited capacity
Bacteriophage ($\lambda$)	$< 25\ \mathrm{kb}$	Efficient delivery to E. coli	More complex handling
BAC (bacterial artificial chromosome)	$100$--$300\ \mathrm{kb}$	Large inserts	Low copy number
YAC (yeast artificial chromosome)	$100$--$2000\ \mathrm{kb}$	Very large inserts; eukaryotic processing	Unstable; low yield

1.3 Procedure for Producing Recombinant DNA

1. Isolation: the target gene is located and cut from donor DNA using a restriction enzyme.
2. Vector preparation: the same restriction enzyme cuts the plasmid vector at a specific site (e.g., within a gene for antibiotic resistance or a reporter gene like lacZ).
3. Ligation: the target gene and the cut plasmid are mixed with DNA ligase. The complementary sticky ends anneal by base pairing, and DNA ligase seals the nicks, producing a recombinant plasmid.
4. Transformation: the recombinant plasmid is introduced into host bacterial cells by:
   • Heat shock: cells are chilled ($4\ ^\circ\mathrm{C}$), mixed with plasmid DNA, briefly heated ($42\ ^\circ\mathrm{C}$, 90 seconds), and placed on ice. The temperature change makes the membrane permeable to DNA.
   • Electroporation: an electric field creates temporary pores in the membrane.
5. Selection: cells are grown on agar plates containing an antibiotic. Only cells that have taken up the plasmid (with the antibiotic resistance gene) survive.
6. Identification: further screening identifies cells with the recombinant plasmid (containing the target gene inserted into the lacZ gene, disrupting it). White colonies (non-functional lacZ) indicate successful insertion; blue colonies (functional lacZ) indicate the plasmid without insertion.

1.4 Applications

• Recombinant human insulin: produced by E. coli with the human insulin gene. Structurally identical to human insulin, eliminating immune reactions associated with animal-derived insulin.
• Factor VIII: blood clotting factor for treating haemophilia, produced by genetically modified mammalian cells (which perform the necessary post-translational modifications).
• GM crops: herbicide resistance (e.g., BAR gene), pest resistance (Bt toxin gene), nutritional enhancement (Golden Rice with beta-carotene).

2. Polymerase Chain Reaction (PCR)

2.1 Standard PCR

PCR amplifies a specific DNA sequence in vitro. For details of the basic mechanism, see Genetics and DNA.

2.2 Quantitative PCR (qPCR)

Real-time PCR (qPCR) allows quantification of the initial amount of DNA in a sample by measuring the accumulation of amplified DNA during the PCR cycles, in real time.

Methods of detection:

• SYBR Green: a fluorescent dye that intercalates into double-stranded DNA. Fluorescence increases proportionally to the amount of dsDNA produced. Simple but non-specific (binds to any dsDNA, including primer-dimers).
• TaqMan probes: sequence-specific oligonucleotide probes labelled with a fluorescent reporter at one end and a quencher at the other. When the probe is intact, the quencher absorbs the reporter's fluorescence. During extension, the probe is cleaved by the $5' \to 3'$ exonuclease activity of Taq polymerase, separating reporter from quencher and allowing fluorescence. Highly specific.

The $C_t$ value (threshold cycle) is the PCR cycle at which the fluorescence exceeds a defined threshold. It is inversely proportional to the logarithm of the initial template quantity:

$C_t \propto -\log(\text{initial template amount})$

A lower $C_t$ value indicates more initial template.

Worked Example. A qPCR assay gives $C_t = 25$ for a sample and $C_t = 28$ for a standard with known concentration of $10^4$ copies. If each $C_t$ difference of 1 represents a doubling:

Number of copies in sample $= 10^4 \times 2^{(28-25)} = 10^4 \times 2^3 = 10^4 \times 8 = 80000$ copies.

2.3 Reverse Transcription PCR (RT-PCR)

RT-PCR is used to amplify RNA. First, reverse transcriptase converts the RNA template into complementary DNA (cDNA). The cDNA is then amplified by standard PCR. This is essential for studying gene expression (mRNA levels), detecting RNA viruses (e.g., SARS-CoV-2, HIV), and analysing transcriptomes.

3. Gel Electrophoresis

3.1 DNA Gel Electrophoresis

DNA fragments are separated by size through an agarose gel under an electric field. For details, see Genetics and DNA.

3.2 Protein Electrophoresis (SDS-PAGE)

SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) separates proteins by molecular mass:

1. Proteins are denatured by heating with SDS (which gives them a uniform negative charge) and $\beta$-mercaptoethanol (which breaks disulfide bridges).
2. The denatured proteins are loaded into wells in a polyacrylamide gel.
3. An electric field is applied; proteins migrate towards the positive electrode.
4. Smaller proteins travel faster through the gel matrix.
5. A protein ladder (proteins of known molecular mass) is used to estimate the mass of unknown proteins.

3.3 Southern, Northern, and Western Blotting

Technique	Target	Probe/Antibody	Purpose
Southern blot	DNA fragments	Radioactive DNA probe	Identify specific DNA sequences
Northern blot	RNA fragments	Radioactive DNA probe	Measure gene expression (mRNA levels)
Western blot	Proteins	Specific antibody	Detect specific proteins

4. DNA Sequencing

4.1 Sanger Sequencing (Chain-Termination Method)

Developed by Frederick Sanger (1977). For details, see Genetics and DNA.

4.2 Next-Generation Sequencing (NGS)

NGS methods enable massively parallel sequencing of millions of DNA fragments simultaneously:

• Illumina sequencing: DNA fragments are attached to a flow cell and amplified by bridge PCR to form clusters. Sequencing-by-synthesis uses fluorescently labelled reversible terminators; each cycle adds one nucleotide and captures an image.
• Pyrosequencing (454): detects the release of pyrophosphate ($\mathrm{PP_i}$) when a nucleotide is incorporated, which is converted to light by a cascade of enzymatic reactions.

NGS has dramatically reduced the cost and time required for genome sequencing (the Human Genome Project took 13 years and cost $2.7 billion; today a human genome can be sequenced in hours for under$1000).

5. Genetic Engineering in Medicine and Agriculture

5.1 Gene Therapy

Gene therapy involves introducing functional copies of a gene into a patient's cells to compensate for a defective gene. It is a potential treatment for genetic disorders caused by single-gene defects (e.g., cystic fibrosis, severe combined immunodeficiency, sickle cell anaemia).

Somatic gene therapy: the functional gene is introduced into the patient's body cells (not gametes). The changes are not inherited.

• In vivo: the gene is delivered directly to the patient's body using a viral vector (e.g., adenovirus, lentivirus) or a non-viral method (liposomes, nanoparticles).
• Ex vivo: cells are removed from the patient, the functional gene is introduced in the laboratory (using a viral vector), the modified cells are selected and expanded, and then returned to the patient.

Germ line gene therapy: the functional gene is introduced into gametes or early embryos, producing changes that are inherited by future generations. This is currently illegal in most countries due to ethical concerns and the risk of unintended consequences.

Challenges of gene therapy:

• Delivering the gene to the correct cells and ensuring it is expressed at the right level.
• Immune response to the viral vector.
• The therapeutic effect may be temporary (if the modified cells are not stem cells and do not divide indefinitely).
• Risk of insertional mutagenesis (the viral DNA may insert near an oncogene, activating it).
• Ethical concerns about enhancement (designer babies).

5.2 Stem Cells

Stem cells are undifferentiated cells with the capacity for self-renewal (mitosis producing identical stem cells) and differentiation into specialised cell types.

Type	Source	Potency	Ethical Issues
Embryonic (ESC)	Inner cell mass of blastocyst (5--7 days)	Totipotent/pluripotent	Significant (destruction of embryo)
Adult	Bone marrow, adipose tissue, brain	Multipotent	Fewer
Induced pluripotent (iPSC)	Adult cells reprogrammed with transcription factors (Oct4, Sox2, Klf4, c-Myc)	Pluripotent	Minimal (no embryos)

Therapeutic cloning (somatic cell nuclear transfer, SCNT): the nucleus from a patient's somatic cell is transferred into an enucleated egg cell. The resulting embryo is allowed to develop to the blastocyst stage, and embryonic stem cells are harvested. These cells are genetically identical to the patient and can be directed to differentiate into the required cell type for transplantation (e.g., insulin-producing beta cells for Type 1 diabetes, dopaminergic neurons for Parkinson's disease). The embryo is not implanted into a uterus.

Ethical considerations of stem cell research:

• Embryonic stem cells require the destruction of human embryos (some consider this morally equivalent to taking a life).
• Therapeutic cloning creates embryos that are destroyed after stem cell extraction.
• iPSCs offer an ethically less contentious alternative but are technically more challenging (lower efficiency, risk of incomplete reprogramming).
• The potential for stem cells to be used for enhancement rather than therapy raises ethical concerns about equity and access.

6. CRISPR-Cas9

6.1 Mechanism

CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) is a gene editing tool derived from a bacterial immune defence system.

Components:

1. Cas9 protein: an endonuclease enzyme that cuts double-stranded DNA.
2. Guide RNA (gRNA): a 20-nucleotide RNA sequence complementary to the target DNA sequence. The gRNA guides Cas9 to the correct location.
3. PAM sequence: a short DNA sequence (5'-NGG-3' for Streptococcus pyogenes Cas9) immediately adjacent to the target. Cas9 requires a PAM to bind and cut.

Mechanism:

1. The gRNA is designed to be complementary to the target DNA sequence.
2. The gRNA-Cas9 complex searches the genome for the target sequence adjacent to a PAM.
3. When the gRNA base-pairs with the target DNA and the PAM is recognised, Cas9 cuts both strands of the DNA, creating a double-strand break (DSB).
4. The cell repairs the DSB by one of two mechanisms:
   • Non-homologous end joining (NHEJ): the broken ends are joined directly, often introducing small insertions or deletions (indels) that can disrupt the gene (gene knockout).
   • Homology-directed repair (HDR): if a donor DNA template with the desired sequence is provided, the cell uses it as a template to repair the break, introducing the desired sequence (gene knock-in or correction).

6.2 Applications

• Gene knockout: disrupting a gene to study its function (research) or to disable a disease-causing gene (therapy).
• Gene correction: repairing a disease-causing mutation in situ (e.g., sickle cell anaemia, beta-thalassaemia).
• Gene regulation: fusing a catalytically dead Cas9 (dCas9) with transcriptional activators or repressors to up- or down-regulate gene expression without cutting DNA.
• Diagnostics: SHERLOCK and DETECTR use Cas13/Cas12 to detect specific RNA/DNA sequences with high sensitivity, applied to pathogen detection (e.g., SARS-CoV-2).

6.3 Ethical and Safety Concerns

• Off-target effects: Cas9 may cut at sites with partial homology to the gRNA, causing unintended mutations.
• Mosaicism: in embryos, the edit may not occur in all cells, producing individuals with a mixture of edited and unedited cells.
• Germline editing: edits to germ cells or embryos are heritable. The 2018 case of He Jiankui, who edited the CCR5 gene in human embryos to confer HIV resistance, was widely condemned.
• Enhancement: CRISPR could be used for non-therapeutic enhancement (e.g., increased intelligence, athletic ability), raising concerns about equity and "designer babies."

7. Bioinformatics

7.1 Definition

Bioinformatics is the application of computational tools to store, analyse, and interpret biological data, particularly DNA and protein sequences.

7.2 Key Bioinformatics Activities

• Sequence alignment: comparing DNA or protein sequences to identify regions of similarity (homology). Tools: BLAST (Basic Local Alignment Search Tool), ClustalW.
• Genome annotation: identifying genes, regulatory elements, and other functional features within a genome sequence.
• Phylogenetic analysis: constructing evolutionary trees from sequence data.
• Protein structure prediction: using algorithms (e.g., AlphaFold) to predict the 3D structure of proteins from their amino acid sequence.
• Genome-wide association studies (GWAS): scanning genomes of large populations to identify genetic variants associated with diseases or traits.

7.3 Databases

Database	Content
GenBank	Nucleotide sequences
UniProt	Protein sequences and function
OMIM	Human genes and genetic disorders
Ensembl	Vertebrate genomes
PDB	Protein 3D structures

8. The Microbiome

8.1 Definition and Importance

The human microbiome is the collective genome of all microorganisms (bacteria, archaea, fungi, viruses) that live on and in the human body. The human gut microbiome alone contains approximately $3 \times 10^{13}$ bacterial cells -- roughly equal to the number of human cells in the body.

8.2 Functions of the Gut Microbiome

• Digestion: gut bacteria ferment dietary fibre to produce short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate, which provide energy for colonocytes and have anti-inflammatory effects.
• Immune system development: exposure to gut bacteria in early life is essential for normal immune system maturation. The microbiome helps train the immune system to distinguish harmless commensals from pathogens.
• Vitamin synthesis: gut bacteria produce vitamin K and some B vitamins.
• Protection against pathogens: commensal bacteria compete with pathogens for nutrients and attachment sites, and produce antimicrobial substances (bacteriocins).
• Metabolic health: the composition of the gut microbiome is linked to obesity, type 2 diabetes, and cardiovascular disease.

8.3 Dysbiosis

Dysbiosis (imbalance of the microbiome) is associated with:

• Inflammatory bowel disease (Crohn's disease, ulcerative colitis).
• Obesity and metabolic syndrome.
• Mental health conditions (via the gut-brain axis).
• Allergies and autoimmune diseases.

9. Practical Skills

9.1 Calculations in Biotechnology

Worked Example 1: PCR product yield. A PCR reaction starts with 3 copies of a target sequence. After 32 cycles, how many copies are produced?

$N = 3 \times 2^{32} = 3 \times 4294967296 = 1.29 \times 10^{10}\ \text{copies}$

Worked Example 2: Restriction fragment analysis. A plasmid of $5000\ \mathrm{bp}$ is cut with EcoRI at position $1000\ \mathrm{bp}$ and with BamHI at position $3500\ \mathrm{bp}$. How many fragments are produced and what are their sizes?

EcoRI cuts at $1000\ \mathrm{bp}$, producing fragments of $1000\ \mathrm{bp}$ and $4000\ \mathrm{bp}$. BamHI cuts the $4000\ \mathrm{bp}$ fragment at position $3500\ \mathrm{bp}$, producing fragments of $2500\ \mathrm{bp}$ ($3500 - 1000$) and $1500\ \mathrm{bp}$ ($5000 - 3500$).

Final fragments: $1000\ \mathrm{bp}$, $2500\ \mathrm{bp}$, and $1500\ \mathrm{bp}$ (three fragments).

Worked Example 3: Calculating DNA concentration from absorbance. A DNA solution has an absorbance of 0.40 at $260\ \mathrm{nm}$. The relationship between absorbance and double-stranded DNA concentration is: $A_{260} = 1.0$ for $50\ \mu\mathrm{g\ mL^{-1}}$ dsDNA.

Concentration $= \frac{0.40}{1.0} \times 50 = 20\ \mu\mathrm{g\ mL^{-1}}$.

warning

Common Pitfall Students often confuse Southern, Northern, and Western blotting. Southern = DNA, Northern = RNA, Western = protein. The mnemonic "SNOW Drop" (Southern, Northern, Western -- DNA, RNA, protein) may help. Students also frequently forget that PCR does not require living organisms or bacterial cells -- it is an entirely in vitro technique.

Practice Problems

Details

Problem 1

Describe the process of producing recombinant human insulin using genetic engineering. Include reference to restriction enzymes, DNA ligase, vectors, and selection methods. (6 marks)

Answer. (1) The human insulin gene is located and cut from human DNA using a restriction enzyme (e.g., EcoRI), producing sticky ends. (2) The same restriction enzyme cuts a plasmid vector at a specific site, often within the lacZ gene. (3) The insulin gene and the cut plasmid are mixed with DNA ligase, which joins them by forming phosphodiester bonds, producing a recombinant plasmid. (4) The recombinant plasmid is introduced into E. coli host cells by transformation (heat shock or electroporation). (5) Transformed bacteria are selected by growing them on agar plates containing ampicillin. Only bacteria that have taken up the plasmid (which carries an ampicillin resistance gene) survive. (6) To distinguish bacteria with the recombinant plasmid from those with the original plasmid, bacteria are grown on plates containing X-gal and IPTG. Bacteria with the original plasmid produce functional $\beta$-galactosidase (from the intact lacZ gene) and form blue colonies. Bacteria with the recombinant plasmid have the insulin gene inserted into lacZ, disrupting it, and form white colonies. (7) White colonies are selected and grown in large fermenters. Insulin is extracted and purified.

If you get this wrong, revise: Procedure for Producing Recombinant DNA

Details

Problem 2

Explain how CRISPR-Cas9 can be used to correct a disease-causing mutation. In your answer, describe the roles of the guide RNA, Cas9 protein, PAM sequence, and the cell's DNA repair mechanisms. (6 marks)

Answer. CRISPR-Cas9 is a gene editing tool that can precisely cut DNA at a specific location. A guide RNA (gRNA) is designed to be complementary to the target DNA sequence containing the disease-causing mutation. The gRNA-Cas9 complex scans the genome for the target sequence adjacent to a PAM (protospacer adjacent motif, typically 5'-NGG-3'). When the gRNA base-pairs with the target and the PAM is recognised, Cas9 cuts both strands of the DNA, creating a double-strand break (DSB). To correct the mutation, a donor DNA template is provided that contains the correct (wild-type) sequence flanked by regions homologous to the target. The cell repairs the DSB using homology-directed repair (HDR), using the donor template as a guide to insert the correct sequence. This corrects the mutation. If HDR does not occur, the cell may use non-homologous end joining (NHEJ), which can introduce indels that disrupt the gene further. The efficiency of HDR can be increased by using modified Cas9 (nickase versions that create single-strand breaks, which favour HDR).

If you get this wrong, revise: CRISPR-Cas9

Details

Problem 3

Compare and contrast somatic gene therapy and germ line gene therapy. Discuss the ethical issues associated with each approach. (5 marks)

Answer. Somatic gene therapy involves introducing a functional gene into the patient's body cells (somatic cells). The changes affect only the treated individual and are not inherited by offspring. It is used to treat conditions such as cystic fibrosis, SCID, and haemophilia. Germ line gene therapy involves modifying the DNA in gametes or early embryos, producing changes that are inherited by all cells of the organism and can be passed to future generations. It could potentially eliminate genetic diseases from a family line permanently. Ethical issues: somatic gene therapy is generally accepted because it is analogous to conventional medical treatment -- the patient consents, and the changes are not heritable. Germ line gene therapy is widely considered unethical because: (1) the embryo cannot consent; (2) changes are heritable, affecting future generations who cannot consent; (3) there is a risk of off-target effects with unpredictable long-term consequences for the gene pool; (4) it could be used for enhancement rather than therapy; (5) it raises concerns about "designer babies" and the commodification of human life. Germ line gene therapy is currently illegal in most countries.

If you get this wrong, revise: Gene Therapy

Details

Problem 4

A plasmid has a total length of $4500\ \mathrm{bp}$. It is cut with two restriction enzymes: EcoRI cuts at position $900\ \mathrm{bp}$, and HindIII cuts at position $2700\ \mathrm{bp}$. (a) How many fragments are produced? (b) What are their sizes? (c) If the fragments are separated by gel electrophoresis, which fragment will travel furthest from the wells?

Answer. (a) Two cuts produce three fragments.

(b) Fragment 1: from position 0 to 900 = $900\ \mathrm{bp}$ (circular plasmid) or from the start of the linearised plasmid to the first cut. Fragment 2: from position 900 to 2700 = $1800\ \mathrm{bp}$. Fragment 3: from position 2700 to 4500 = $1800\ \mathrm{bp}$.

The three fragments are: $900\ \mathrm{bp}$, $1800\ \mathrm{bp}$, and $1800\ \mathrm{bp}$.

(c) The smallest fragment ($900\ \mathrm{bp}$) will travel furthest from the wells because smaller DNA fragments migrate faster through the gel matrix.

If you get this wrong, revise: Calculations in Biotechnology

Details

Problem 5

Explain the advantages and disadvantages of using embryonic stem cells compared to adult stem cells for medical research and therapy. (5 marks)

Answer. Embryonic stem cells (ESCs) are pluripotent -- they can differentiate into any cell type in the body, making them more versatile for therapy. Adult stem cells are multipotent -- they can only differentiate into a limited range of cell types within their tissue of origin. ESCs can divide indefinitely in culture, providing an unlimited supply, whereas adult stem cells have a limited capacity for self-renewal. However, ESCs have significant disadvantages: they are derived from embryos, which must be destroyed (raising ethical objections about the moral status of the embryo); they carry a risk of teratoma formation (tumours) if transplanted without full differentiation; and they require immunosuppression if the donor and recipient are not genetically matched. Adult stem cells avoid the ethical issues associated with embryo destruction and can sometimes be harvested from the patient's own body (autologous transplant), eliminating immune rejection. However, adult stem cells are rare, difficult to isolate and expand in culture, and have limited differentiation potential. Induced pluripotent stem cells (iPSCs) offer a compromise: they are pluripotent like ESCs but derived from adult cells, avoiding embryo destruction.

If you get this wrong, revise: Stem Cells

10. Genetic Engineering in Agriculture: Golden Rice

10.1 The Problem: Vitamin A Deficiency

Vitamin A deficiency (VAD) affects approximately 250 million children worldwide, particularly in Southeast Asia and sub-Saharan Africa. VAD causes xerophthalmia (dry eyes), night blindness, and in severe cases, total blindness and increased susceptibility to infections. Rice is a staple food for billions of people but contains no $\beta$-carotene (provitamin A) in the endosperm (the edible white part).

10.2 The Solution: Engineering Provitamin A Biosynthesis

Golden Rice was developed by introducing two genes from other species into rice:

1. psy (phytoene synthase) from daffodil (Narcissus pseudonarcissus) -- later replaced by the maize psy gene for higher expression.
2. crtI (phytoene desaturase) from the soil bacterium Erwinia uredovora (now reclassified as Pantoea ananatis).

These genes enable the rice endosperm to produce $\beta$-carotene from geranylgeranyl diphosphate (GGPP), a precursor already present in the endosperm:

$\text{GGPP} \xrightarrow{\text{psy}} \text{phytoene} \xrightarrow{\text{crtI}} \text{lycopene} \xrightarrow{\text{lcy (endogenous)}} \beta\text{-carotene}$

The lycopene cyclase (lcy) step is catalysed by an enzyme already present in rice (endogenous gene).

10.3 Golden Rice 2

Golden Rice 1 produced insufficient $\beta$-carotene ($1.6\ \mu\mathrm{g\ g^{-1}}$). Golden Rice 2 replaced the daffodil psy gene with a maize psy gene, which has higher expression in rice endosperm, increasing $\beta$-carotene to $23\ \mu\mathrm{g\ g^{-1}}$ (a 14-fold improvement). This level is sufficient to provide the recommended daily intake of vitamin A from a typical serving of rice.

10.4 Ethical and Practical Considerations

Argument For	Argument Against
Addresses a major public health problem (VAD blindness)	Concerns about corporate control of food supply (patents on GM crops)
Rice is self-pollinating, so transgenes do not spread easily to wild relatives	Gene flow to wild rice species could have unintended ecological consequences
Golden Rice seeds are distributed free to subsistence farmers (humanitarian licence)	Some argue that VAD is better addressed by dietary diversification (eating more vegetables) rather than GM technology
Reduces reliance on vitamin A supplements (cost, distribution logistics)	Long-term health effects of consuming GM foods are unknown (though no evidence of harm to date)
Could be combined with other traits (drought resistance, pest resistance)	Public opposition to GM food may prevent adoption

11. Gene Therapy

11.1 Somatic Gene Therapy

Somatic gene therapy involves inserting a functional copy of a gene into the patient's body cells (somatic cells). This does not affect the patient's germ cells, so the change is not inherited by offspring.

Vectors for gene delivery:

Vector	Advantages	Disadvantages
Retrovirus (e.g., lentivirus)	Integrates into host genome, providing permanent expression	Risk of insertional mutagenesis (activating oncogenes); only infects dividing cells
Adenovirus	Does not integrate into genome; high transduction efficiency	Transient expression (lost as cells divide); immune response
Adeno-associated virus (AAV)	Low immunogenicity; long-term expression in non-dividing cells	Small capacity ($< 5\ \mathrm{kb}$); expensive to produce
Liposomes (lipid nanoparticles)	Non-viral; no risk of viral infection; can carry larger DNA	Low transfection efficiency; transient expression
Naked DNA injection	Simple; no vector needed	Very low efficiency

11.2 Germline Gene Therapy

Germline gene therapy involves modifying the DNA in germ cells (sperm, eggs) or early embryos. The changes would be inherited by all cells of the resulting individual and passed to future generations.

Germline gene therapy is currently illegal in most countries due to:

• Ethical concerns about modifying the human germline ("designer babies").
• Unknown long-term consequences for future generations.
• Risk of off-target effects (unintended mutations).
• Social justice concerns (access limited to the wealthy).

11.3 Gene Therapy Success: Severe Combined Immunodeficiency (SCID)

SCID ("bubble boy disease") is caused by mutations in genes essential for immune cell development (e.g., IL2RG on the X chromosome, causing X-linked SCID). In 2000, gene therapy using a retroviral vector successfully restored immune function in several SCID patients. However, 5 of 20 patients developed leukaemia because the retrovirus inserted near the LMO2 oncogene, activating it. This highlighted the risk of insertional mutagenesis and led to improved vector designs with safer integration profiles.

12. Bioinformatics in Depth

12.1 BLAST (Basic Local Alignment Search Tool)

BLAST is the most widely used bioinformatics tool. It compares a query DNA or protein sequence against a database of known sequences to find similar sequences.

How BLAST works:

1. The query sequence is broken into short "words" (typically 3 amino acids for protein BLAST).
2. The database is scanned for exact matches to these words.
3. For each exact match found, BLAST extends the alignment in both directions.
4. High-scoring segment pairs (HSPs) are identified using a substitution matrix (e.g., BLOSUM62 for proteins).
5. Statistical significance is assessed using the E-value (expect value).

E-value interpretation:

• E-value $< 10^{-10}$: highly significant match (almost certainly homologous).
• E-value $< 10^{-5}$: significant match (likely homologous).
• E-value $> 0.01$: not significant (match may be due to chance).

12.2 Multiple Sequence Alignment and Phylogenetic Trees

When comparing multiple sequences (e.g., the same gene from different species), a multiple sequence alignment (MSA) is performed using algorithms such as ClustalW or MUSCLE. The aligned sequences are then used to construct a phylogenetic tree.

Tree-building methods:

Method	Principle	Speed	Accuracy
UPGMA (unweighted pair group method with arithmetic mean)	Clusters sequences by pairwise similarity; assumes a molecular clock	Fast	Lower (assumes equal rates)
Neighbour-joining	Minimises total branch length; does not assume a molecular clock	Fast	Moderate
Maximum parsimony	Chooses the tree requiring the fewest evolutionary changes	Slow	Moderate
Maximum likelihood	Chooses the tree with the highest probability given an evolutionary model	Very slow	High
Bayesian inference	Uses probability distributions to estimate the most likely tree	Very slow	Highest

12.3 Worked Example: Calculating Genetic Distance

Two species have the following aligned DNA sequences for a 20 bp region:

Species A: ATG-CCT-AGG-TCA-GCT-AGA-TCC Species B: ATG-CCT-AGG-TCA-GCT-AGA-TCC Species C: ATG-CCT-AAG-TCA-GCT-AGA-TCC Species D: ATG-CCT-AAG-TCA-GCA-AGA-TCC

Counting differences:

• A vs B: 0 differences
• A vs C: 1 difference (position 10: G $\to$ A)
• A vs D: 2 differences (position 10: G $\to$ A; position 16: T $\to$ A)
• B vs C: 1 difference
• B vs D: 2 differences
• C vs D: 1 difference

Genetic distance matrix:

	A	B	C	D
A	0	0.00	0.05	0.10
B		0	0.05	0.10
C			0	0.05
D				0

Species A and B are most closely related (identical in this region). Species C is equally distant from A and B. Species D is the most divergent.

13. Tissue Culture and Micropropagation

13.1 Principles

Plant tissue culture (micropropagation) involves growing plants from small pieces of plant tissue (explants) on an artificial nutrient medium under sterile conditions. It exploits the property of totipotency: the ability of any plant cell to develop into a complete organism.

13.2 Stages of Micropropagation

1. Stage 0: Selection and preparation. A healthy, disease-free mother plant is selected. Explants (leaf discs, stem sections, meristems) are surface-sterilised using sodium hypochlorite or ethanol.
2. Stage 1: Initiation. Explants are placed on a nutrient medium containing:
   • Macronutrients: N, P, K, Ca, Mg, S.
   • Micronutrients: Fe, Mn, Zn, Cu, B, Mo.
   • Carbon source: sucrose (since the explant cannot photosynthesise).
   • Vitamins: thiamine, nicotinic acid.
   • Plant growth regulators: auxin (e.g., 2,4-D) and cytokinin (e.g., BAP). The auxin:cytokinin ratio determines the response:
     • High auxin : low cytokinin $\to$ root formation.
     • Low auxin : high cytokinin $\to$ shoot formation.
     • Balanced ratio $\to$ callus formation (undifferentiated cell mass).
   • Gelling agent: agar.
   • The medium is solidified with agar and sterilised by autoclaving.
3. Stage 2: Multiplication. Callus or shoot tips are subcultured onto fresh medium to produce multiple shoots. Each shoot can be further divided, allowing exponential multiplication.
4. Stage 3: Rooting. Individual shoots are transferred to a rooting medium (high auxin) to induce root formation, producing complete plantlets.
5. Stage 4: Acclimatisation (hardening off). Plantlets are transferred from the sterile, high-humidity culture vessel to soil. This is the most critical stage because the plantlets must transition from heterotrophic growth (using sucrose from the medium) to autotrophic growth (photosynthesis) and develop a functional cuticle to prevent water loss.

13.3 Applications

• Mass production of ornamental plants (orchids, ferns) and crop plants (bananas, potatoes, strawberries).
• Production of disease-free plants (e.g., virus-free potatoes by culturing meristem tissue, which typically has low viral load).
• Conservation of endangered plant species.
• Production of secondary metabolites (e.g., shikonin, a dye, from cell cultures of Lithospermum).

13.4 Advantages and Disadvantages

Advantages	Disadvantages
Large numbers of identical plants (clones) produced rapidly	Genetic uniformity makes all plants equally susceptible to the same disease
Disease-free plants can be produced	Requires sterile conditions and skilled labour
Year-round production, independent of seasons	Expensive equipment and consumables
Enables conservation of rare species	Somaclonal variation (genetic changes during tissue culture) can reduce quality
Small amount of parent tissue needed	Some species are difficult to culture

14. Fermentation and Bioreactors

14.1 Types of Fermentation

Type	Organism	Conditions	Products
Aerobic	Aspergillus niger (fungus)	Aerate, $30$ degrees C, pH 2--3	Citric acid
Anaerobic	Saccharomyces cerevisiae (yeast)	No aeration, $30$ degrees C, pH 4--6	Ethanol, $\mathrm{CO_2}$
Continuous	Escherichia coli (bacterium)	Continuous nutrient supply	Insulin, growth hormone

14.2 Batch vs Continuous Fermentation

Feature	Batch Fermentation	Continuous Fermentation
Setup	Fixed volume of medium; closed system	Constant inflow of fresh medium; constant outflow of product
Growth phases	All four phases (lag, log, stationary, death) occur	Cells maintained in exponential (log) phase
Product yield	Varies over time; harvest at end of run	Constant, steady-state yield
Contamination risk	Lower (sealed vessel)	Higher (open system for extended periods)
Cost	Lower initial cost; labour-intensive	Higher initial cost; automated
Best for	Secondary metabolites (e.g., antibiotics, produced in stationary phase)	Primary metabolites (e.g., insulin, produced during exponential growth)

14.3 Optimising Fermentation Conditions

To maximise product yield, the following factors must be optimised:

• Temperature: affects enzyme activity and growth rate. Each organism has an optimum temperature (e.g., $37$ degrees C for E. coli, $30$ degrees C for S. cerevisiae). Fermentation generates heat, so cooling systems are needed.
• pH: affects enzyme activity and membrane transport. Buffers or acid/base addition maintain pH.
• Oxygen concentration: aerobic fermentations require continuous aeration (sparging with sterile air). Dissolved oxygen probes monitor $\mathrm{O_2}$ levels.
• Nutrient concentration: limiting nutrients can control growth rate (chemostat). Carbon, nitrogen, and phosphate sources must be optimised.
• Stirring: ensures uniform mixing of nutrients, temperature, and $\mathrm{O_2}$.
• Foam control: fermentation produces foam (from proteins and gas bubbles), which can block air filters and reduce vessel volume. Anti-foaming agents (silicone-based) are added automatically.

14.4 Downstream Processing

After fermentation, the product must be extracted and purified:

1. Filtration or centrifugation: separates cells from the culture medium.
2. Cell disruption (if product is intracellular): sonication, enzymatic lysis, or high-pressure homogenisation.
3. Chromatography: separates the product from other molecules based on size (gel filtration), charge (ion exchange), or affinity (affinity chromatography using a specific antibody or ligand).
4. Ultrafiltration/diafiltration: concentrates and desalts the product.

15. Ethical Issues in Biotechnology

15.1 Key Ethical Principles

Principle	Description
Beneficence	Technology should benefit humanity (e.g., curing disease, feeding the hungry)
Non-maleficence	Technology should not cause harm (assessing risks of GM crops, gene therapy)
Autonomy	Individuals have the right to make informed choices (e.g., informed consent for genetic testing)
Justice	Benefits and risks should be distributed fairly (avoiding "genetic divide" between rich and poor)
Precautionary principle	Where there is scientific uncertainty about potential harm, precautionary measures should be taken

15.2 Genetic Testing and Screening

Prenatal genetic testing (amniocentesis, chorionic villus sampling) can detect chromosomal abnormalities (e.g., Down syndrome) and single-gene disorders (e.g., cystic fibrosis, sickle cell anaemia) before birth.

Preimplantation genetic diagnosis (PGD) involves testing embryos created by IVF for genetic disorders before implantation. Only unaffected embryos are implanted.

Ethical concerns:

• Should parents be allowed to select embryos based on non-medical traits (sex, eye colour)? This is sometimes called "designer babies" and is illegal in many countries.
• What about disorders with variable penetrance (e.g., BRCA1 mutations increase breast cancer risk but do not guarantee it)?
• The psychological impact of genetic information on individuals and families.
• Genetic discrimination by employers or insurance companies (addressed by legislation such as the Genetic Information Nondiscrimination Act, GINA, in the US).

15.3 GM Crops: Weighing the Evidence

Environmental concerns:

• Gene flow to wild relatives could create "superweeds" (e.g., herbicide resistance transferred to weedy relatives of oilseed rape).
• Impact on non-target organisms (e.g., Bt toxin from GM maize may affect butterflies -- though field evidence is limited).
• Loss of biodiversity if GM monocultures replace diverse traditional varieties.

Socioeconomic concerns:

• Patents on GM seeds mean farmers must buy new seeds each year (cannot save seed), increasing dependence on multinational corporations.
• Smallholder farmers in developing countries may not benefit if the technology is too expensive.

Scientific consensus: the World Health Organization, the American Medical Association, and the Royal Society have all concluded that GM foods currently available are safe to eat and no different in safety from conventional foods. However, each new GM crop must be assessed on a case-by-case basis.

16. The Microbiome in Health and Disease

16.1 Composition

The human gut microbiome consists of approximately $10^{13}$--$10^{14}$ bacteria from over 1000 species, predominantly from the phyla Firmicutes and Bacteroidetes. The microbiome varies between individuals and is influenced by diet, age, medication (especially antibiotics), and environment.

16.2 Functions of the Gut Microbiome

Function	Mechanism
Fermentation of dietary fibre	Bacteria produce short-chain fatty acids (SCFAs): butyrate, propionate, acetate. Butyrate is the primary energy source for colonocytes and has anti-inflammatory properties.
Vitamin synthesis	Bacteria synthesise vitamin K and several B vitamins (B12, folate, riboflavin, biotin).
Immune system development	Bacterial antigens stimulate the development of gut-associated lymphoid tissue (GALT) and regulatory T cells.
Protection against pathogens	Commensal bacteria compete with pathogens for nutrients and adhesion sites; they produce antimicrobial peptides (bacteriocins).
Metabolism of xenobiotics	Bacteria modify drugs and toxins, affecting their absorption, efficacy, and toxicity.

16.3 Dysbiosis

Dysbiosis is a disruption of the normal composition of the microbiome, associated with:

• Inflammatory bowel disease (IBD): reduced diversity; increased Faecalibacterium prausnitzii is protective.
• Obesity: altered Firmicutes:Bacteroidetes ratio (controversial; findings are inconsistent between studies).
• Type 2 diabetes: reduced abundance of butyrate-producing bacteria.
• Mental health: the "gut-brain axis" -- the vagus nerve and immune signals communicate between the gut and brain. Dysbiosis has been linked to anxiety, depression, and autism spectrum disorder.
• Clostridioides difficile infection: broad-spectrum antibiotics kill commensal bacteria, allowing C. difficile to overgrow. Treated with faecal microbiota transplantation (FMT) -- transferring stool from a healthy donor to the patient's colon, which restores a healthy microbiome.

16.4 Probiotics and Prebiotics

Probiotics are live microorganisms (e.g., Lactobacillus, Bifidobacterium) that, when administered in adequate amounts, confer a health benefit. Evidence supports their use for antibiotic-associated diarrhoea and pouchitis.

Prebiotics are non-digestible food components (e.g., inulin, fructooligosaccharides) that selectively stimulate the growth and activity of beneficial gut bacteria.

Synbiotics combine probiotics and prebiotics.

warning

Common Pitfall Students often confuse antibiotics (which kill bacteria) with probiotics (which add beneficial bacteria). Antibiotics can disrupt the microbiome and cause side effects (diarrhoea, thrush). Probiotics may help restore the microbiome after antibiotic treatment, but they should not be taken simultaneously with antibiotics (the antibiotic would kill the probiotic bacteria).

17. Genetically Modified Organisms: Case Studies

17.1 Bt Cotton

Bt cotton has been engineered to express a gene from the bacterium Bacillus thuringiensis that produces Bt toxin (Cry protein). When insect pests (e.g., cotton bollworm) ingest Bt cotton tissue, the toxin is activated in their alkaline gut, binds to specific receptors on the gut epithelial cells, and forms pores, causing cell lysis and death of the insect.

Advantages:

• Reduces the need for chemical insecticide sprays (beneficial for the environment and farmer health).
• Increases yield by reducing pest damage.
• Bt toxin is specific to certain insect groups and is harmless to humans, livestock, and most beneficial insects.

Disadvantages:

• Resistance can evolve in pest populations (refuges of non-Bt cotton are planted to maintain susceptible alleles in the pest population).
• Concerns about gene flow to wild relatives.
• Seeds are more expensive than conventional varieties.

17.2 Herbicide-Resistant Crops (Roundup Ready)

Crops engineered to be resistant to the herbicide glyphosate (Roundup) by expressing a glyphosate-insensitive version of EPSP synthase (the enzyme glyphosate normally inhibits). This allows farmers to spray glyphosate to kill weeds without harming the crop.

Advantages:

• Simplifies weed management (one herbicide kills all weeds).
• Reduces the need for tillage (reducing soil erosion).
• Enables no-till farming.

Disadvantages:

• Over-reliance on a single herbicide has selected for glyphosate-resistant weeds ("superweeds").
• Glyphosate residues may persist in soil and water.
• Concerns about effects on non-target organisms and human health (controversial; regulatory agencies consider glyphosate safe at approved levels).

17.3 GM Animals

AquAdvantage salmon: genetically modified Atlantic salmon that expresses a growth hormone gene from Chinook salmon, regulated by an ocean pout antifreeze protein promoter. The salmon grows to market size in approximately 18 months instead of 36 months. Approved for human consumption by the FDA (USA) in 2015.

Goats producing antithrombin: goats engineered to express human antithrombin (a blood-clotting protein) in their milk. The protein is purified from the milk and used to treat patients with antithrombin deficiency.

18. Polymerase Chain Reaction: Advanced Topics

18.1 Quantitative PCR (qPCR)

Quantitative PCR (real-time PCR) allows the amount of DNA in a sample to be quantified by measuring the increase in fluorescence during the amplification reaction.

Two main methods:

Method	Principle	Advantages
SYBR Green	A fluorescent dye that binds to double-stranded DNA. Fluorescence increases as more dsDNA is produced.	Simple, cheap
TaqMan probes	A fluorescent probe with a reporter dye and a quencher. When the probe binds to the target sequence and is degraded by Taq polymerase's 5' exonuclease activity, fluorescence is released.	Highly specific; can distinguish between closely related sequences

The threshold cycle ($C_t$) is the cycle number at which the fluorescence exceeds a set threshold. A lower $C_t$ value indicates a higher starting concentration of the target DNA.

18.2 Calculations in qPCR

The amount of DNA doubles with each cycle: after $n$ cycles, the amount of DNA $= \text{initial amount} \times 2^n$.

If Sample A has $C_t = 20$ and Sample B has $C_t = 26$, the difference is 6 cycles. The starting concentration of DNA in Sample A is $2^6 = 64$ times higher than in Sample B.

18.3 Reverse Transcription PCR (RT-PCR)

RT-PCR (not to be confused with real-time PCR/qPCR) is used to detect RNA. The process:

1. Reverse transcription: reverse transcriptase enzyme converts RNA into complementary DNA (cDNA).
2. PCR: the cDNA is amplified using standard PCR.

This technique is widely used to detect RNA viruses (e.g., SARS-CoV-2) and to measure gene expression (by quantifying mRNA levels).

18.4 Primers: Design Considerations

Good PCR primers must:

Criterion	Optimal Value	Reason
Length	18--25 bases	Long enough for specificity, short enough for efficient binding
Melting temperature ($T_m$)	55--65 degrees C	Both primers should have similar $T_m$
GC content	40--60%	Ensures stable binding without excessive non-specific binding
3' end	End in G or C ("GC clamp")	Increases binding stability at the 3' end where extension begins
Self-complementarity	Avoid	Prevents primer-dimer formation (primers annealing to each other)
Repeated sequences	Avoid	Reduces non-specific binding

19. DNA Fingerprinting: Advanced Applications

19.1 Short Tandem Repeats (STRs)

Modern DNA fingerprinting uses short tandem repeats (STRs) -- short (2--6 base pair) sequences repeated in tandem. The number of repeats at a given locus varies between individuals.

The UK National DNA Database uses 10 standard STR loci. The probability of two unrelated individuals having the same profile at all 10 loci is less than 1 in $10^{13}$ (one in ten trillion).

19.2 PCR in Forensics

PCR is essential in forensic DNA analysis because:

• Crime scene samples often contain very small amounts of DNA (trace DNA from skin cells, hair roots, or bodily fluids).
• PCR can amplify the DNA from a single cell to a detectable amount (approximately $10^9$ copies).
• STR loci are short enough to be amplified even from degraded DNA.

19.3 Worked Example: DNA Profile Probability

A suspect's DNA profile matches the crime scene sample at 10 STR loci. The frequency of each allele in the population is:

Locus	Genotype	Population Frequency
D3S1358	15, 16	0.08 $\times$ 0.06 = 0.0048
vWA	17, 18	0.10 $\times$ 0.12 = 0.012
FGA	22, 24	0.15 $\times$ 0.04 = 0.006
...	...	...
D18S51	13, 16	0.07 $\times$ 0.09 = 0.0063

The match probability is the product of the frequencies at all 10 loci. If the average frequency per locus is approximately $0.005$, then:

$\text{Match probability} = (0.005)^{10} = 9.77 \times 10^{-24}$.

This means the probability of a random person matching the DNA profile is approximately 1 in $10^{23}$, making it virtually certain that the suspect is the source of the DNA.

20. Cloning Organisms

20.1 Reproductive Cloning (Somatic Cell Nuclear Transfer)

Dolly the sheep (1996) was the first mammal cloned from an adult somatic cell:

1. A somatic cell (udder cell) was taken from the donor sheep and cultured.
2. An enucleated egg cell (egg cell with its nucleus removed) was taken from a second sheep.
3. The donor nucleus was inserted into the enucleated egg by electrofusion.
4. The reconstructed egg was stimulated with an electric shock to initiate cell division.
5. The resulting embryo was implanted into a surrogate mother.
6. Dolly was born and was genetically identical to the donor sheep (the udder cell donor).

20.2 Therapeutic Cloning

Therapeutic cloning uses the same SCNT technique but the embryo is not implanted. Instead, embryonic stem cells are harvested from the blastocyst (at approximately 5--7 days) and used to grow tissues or organs for medical treatment. Because the stem cells are genetically identical to the patient, they would not be rejected by the immune system.

20.3 Natural Cloning in Plants

Plants can reproduce asexually (vegetatively) by various methods:

Method	Description	Examples
Runners (stolons)	Horizontal stems growing along the ground that produce new roots and shoots at nodes	Strawberry, spider plant
Tubers	Swollen underground stems that can sprout new shoots	Potato
Bulbs	Underground food storage organs with fleshy leaf bases	Onion, daffodil, tulip
Corms	Swollen underground stem bases	Crocus, gladiolus
Cuttings	Pieces of stem or leaf that develop roots when placed in moist conditions	Geranium, sugar cane
Grafting	Joining a scion (shoot) to a rootstock of another plant	Apple, rose, citrus

All of these methods produce clones -- genetically identical offspring. This is advantageous because:

• Desirable characteristics are preserved exactly.
• Rapid reproduction without the need for pollination and seed formation.
• Offspring are mature faster than from seed.

However, there is no genetic variation, so all clones are equally susceptible to the same diseases and environmental changes.

21. Proteomics and Metabolomics

21.1 Proteomics

Proteomics is the large-scale study of the complete set of proteins (the proteome) produced by a genome, tissue, or cell at a given time under specific conditions.

While the genome is fixed, the proteome is dynamic -- it changes with development, disease, and environmental conditions due to alternative splicing, post-translational modifications, and differential gene expression.

Techniques used in proteomics:

Technique	Purpose
2D gel electrophoresis	Separates proteins by charge (first dimension) and by molecular mass (second dimension)
Mass spectrometry	Identifies proteins by measuring the mass-to-charge ratio of peptide fragments
Protein microarrays	Detect protein-protein interactions and measure protein expression levels
X-ray crystallography	Determines the 3D structure of proteins

21.2 Metabolomics

Metabolomics is the study of the complete set of small molecule metabolites (the metabolome) within a biological sample. Metabolomics provides a snapshot of the cell's current metabolic state.

Applications:

• Biomarker discovery: identifying metabolites whose concentration changes in disease (e.g., elevated glucose in diabetes, altered amino acid profiles in cancer).
• Drug discovery: screening for metabolites with therapeutic potential.
• Nutritional science: understanding how diet affects metabolism.
• Environmental toxicology: detecting metabolic changes caused by exposure to pollutants.

warning

Common Pitfall Students often use the terms "genome," "transcriptome," "proteome," and "metabolome" interchangeably. Remember the hierarchy: the genome is the set of all genes (DNA); the transcriptome is the set of all mRNA molecules produced; the proteome is the set of all proteins; the metabolome is the set of all small molecule metabolites. Each level is more dynamic and complex than the one above it.

26. Industrial Biotechnology: Case Studies

26.1 Penicillin Production

Organism: Penicillium chrysogenum (a fungus).

Process:

1. Penicillium is grown in large fermenters (bioreactors) containing a nutrient medium (sugar source, nitrogen source, minerals, precursors such as phenylacetic acid).
2. Conditions: temperature 25--27 degrees C; pH 6.5--7.0; continuous aeration (the fungus is aerobic); agitation to ensure mixing and gas exchange.
3. Penicillin is a secondary metabolite -- it is produced during the stationary phase of growth, when the primary nutrient (glucose) is depleted and the fungus begins to use stored nutrients. This means batch culture is used (not continuous), because the organism must be harvested after the stationary phase.
4. Penicillin is excreted into the medium and extracted by downstream processing (filtration, solvent extraction, chromatography, crystallisation).

Key challenge: penicillin is sensitive to pH (it is hydrolysed at acidic or alkaline pH). The fermentation must be carefully controlled to maintain the optimum pH. The original strain produced very low yields ($\approx 2\ \mathrm{mg\ L^{-1}}$); modern strains (after extensive mutation and selection programmes) produce over $50\ \mathrm{g\ L^{-1}}$.

26.2 Insulin Production by Recombinant E. coli

Process:

1. The human insulin gene (or genes for A and B chains) is inserted into a plasmid vector.
2. The recombinant plasmid is transformed into E. coli.
3. E. coli is grown in large fermenters under controlled conditions.
4. The insulin protein is produced as inclusion bodies (insoluble aggregates in the cytoplasm) because it is a eukaryotic protein that does not fold correctly in E. coli.
5. The inclusion bodies must be solubilised (using denaturants such as urea), and the insulin must be refolded and enzymatically processed (A and B chains are joined by disulphide bonds) to produce functional insulin.

Yield: modern processes produce approximately 100 mg of insulin per litre of culture.

26.3 Bioremediation

Bioremediation uses microorganisms to clean up pollution:

Pollutant	Microorganism	Mechanism
Oil spills	Pseudomonas spp., Alcanivorax	Degrade hydrocarbons in crude oil into $\mathrm{CO_2}$ and water
Heavy metals	Geobacter spp.	Reduce $\mathrm{U^{6+}}$ to $\mathrm{U^{4+}}$, making uranium insoluble and immobilising it
Pesticides	Bacillus spp.	Produce enzymes that break down organophosphate pesticides
Sewage	Mixed microbial communities	Degrade organic matter in primary and secondary treatment
Plastic pollution	Ideonella sakaiensis	Produces PETase enzyme that breaks down PET plastic

Advantages of bioremediation: relatively cheap; environmentally friendly (compared to physical or chemical methods); can be used in situ (at the contaminated site).

Limitations: microorganisms require specific conditions (temperature, pH, nutrients, oxygen); degradation may produce toxic intermediates; may be slower than physical removal.

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25. Ethical Frameworks for Biotechnology Decisions

25.1 Applying Ethical Principles to Specific Cases

Case 1: Using CRISPR to edit human embryos.

Principle	Analysis
Beneficence	Could eliminate devastating genetic diseases (cystic fibrosis, Huntington's disease)
Non-maleficence	Off-target effects could cause new diseases; unknown long-term consequences
Autonomy	The embryo cannot consent; future generations cannot consent to heritable changes
Justice	Initially only available to the wealthy; could exacerbate health inequalities

Case 2: Genetically modified mosquitoes to eliminate malaria.

Principle	Analysis
Beneficence	Could save hundreds of thousands of lives per year
Non-maleficence	Gene drives could have unintended ecological consequences; eliminating a species could affect food webs
Autonomy	People in affected areas may not have been consulted
Justice	Benefits and risks are distributed unevenly (people in Africa bear the ecological risk; people in developed countries develop the technology)

25.2 The Precautionary Principle in Practice

The precautionary principle states that if an action or policy has a suspected risk of causing severe or irreversible harm to the public or the environment, the burden of proof falls on those advocating for the action to demonstrate that it is safe, rather than on those opposing it to demonstrate that it is harmful.

Application to biotechnology:

• GM crops: proponents argue that GM crops have been consumed for decades without evidence of harm; opponents argue that long-term ecological effects cannot yet be known and that precaution requires more testing before widespread adoption.
• Gene drives: the potential for irreversible ecological harm (eliminating a species) means that strict precautionary measures (contained field trials, reversible gene drives) are warranted.
• Germline gene editing: the heritable and irreversible nature of germline changes means that most countries apply the precautionary principle by prohibiting germline editing.

25.3 Balancing Risks and Benefits: A Decision Matrix

When evaluating a biotechnology application, consider:

1. Severity of the problem: how many people are affected? How severe is the disease or condition?
2. Availability of alternatives: are there existing treatments or approaches that could address the problem?
3. Probability of success: how likely is the biotechnology to work as intended?
4. Severity of potential harm: what are the worst-case scenarios?
5. Reversibility: can the intervention be reversed if things go wrong?
6. Distribution of benefits and risks: who benefits and who bears the risks?
7. Public acceptance: is there public support for the technology?

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22. CRISPR-Cas9: Mechanism and Applications in Detail

22.1 The CRISPR-Cas9 System

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a bacterial adaptive immune system that has been repurposed as a genome editing tool. The system has two key components:

1. Guide RNA (gRNA): a synthetic RNA molecule consisting of a CRISPR RNA (crRNA) component that is complementary to the target DNA sequence (approximately 20 nucleotides), and a trans-activating crRNA (tracrRNA) component that binds to the Cas9 protein.

2. Cas9 endonuclease: a protein that cuts both strands of the DNA double helix at the site specified by the gRNA. Cas9 binds to the gRNA, and the gRNA guides Cas9 to the target DNA sequence by complementary base pairing.

Mechanism:

1. The gRNA-Cas9 complex scans the DNA for a PAM sequence (protospacer adjacent motif), which for Streptococcus pyogenes Cas9 is 5'-NGG-3'.
2. When the PAM is found, Cas9 unwinds the DNA adjacent to the PAM.
3. The gRNA base-pairs with the target DNA sequence (approximately 20 nucleotides upstream of the PAM).
4. If base-pairing is sufficiently complementary, Cas9 makes a double-strand break (DSB) 3 base pairs upstream of the PAM.

22.2 Repair of the Double-Strand Break

After Cas9 creates a DSB, the cell repairs it using one of two mechanisms:

Repair Mechanism	Outcome	Use in Gene Editing
Non-homologous end joining (NHEJ)	The broken ends are rejoined, often with small insertions or deletions (indels)	Gene knockout: the indels cause a frameshift, producing a non-functional protein
Homology-directed repair (HDR)	A DNA template with homology to the sequences flanking the break is used as a repair guide	Gene knock-in: a specific sequence (e.g., a corrected gene, a reporter gene) is inserted at the break site

HDR is less efficient than NHEJ and requires a donor DNA template. It typically occurs during the S and G2 phases of the cell cycle (when sister chromatids are available as templates).

22.3 Applications

Application	Description	Status
Sickle cell disease therapy	Correcting the $\beta$-globin gene mutation in haematopoietic stem cells	Clinical trials; promising early results
Cancer immunotherapy	Editing T cells to remove PD-1 receptor (preventing tumour cells from suppressing immune response)	Clinical trials
Diagnostics (SHERLOCK, DETECTR)	Using Cas12/Cas13 collateral cleavage activity to detect specific RNA/DNA sequences	Rapid COVID-19 tests developed
Gene drives	Spreading a gene through a wild population (e.g., making malaria mosquitoes sterile)	Proof of concept; controversial
Agriculture	Drought-resistant wheat, disease-resistant rice, non-browning mushrooms	Approved in USA (2022)

22.4 Off-Target Effects and Ethical Concerns

Off-target effects: Cas9 may cut at sites other than the intended target if the gRNA has sufficient complementarity to other genomic sequences. This could cause unintended mutations, potentially activating oncogenes or disrupting tumour suppressor genes.

Mitigation strategies:

• Careful gRNA design (minimising homology to other genomic sites).
• Using modified Cas9 variants with higher fidelity (e.g., eSpCas9, HiFi Cas9).
• Delivering Cas9 as a ribonucleoprotein (RNP) complex (reduces the time Cas9 is active in the cell).

Ethical concerns:

• Germline editing: editing the human germline (sperm, eggs, or embryos) is currently illegal in most countries. Changes would be heritable.
• Designer babies: the potential to select for non-medical traits (intelligence, physical appearance) raises serious ethical concerns about equity, consent, and the nature of human identity.
• Ecological risks: gene drives could have unintended consequences for ecosystems (e.g., eliminating a mosquito species could affect food webs).
• Equity: gene therapy treatments are extremely expensive (\approx \1$--$2 million per patient), creating a "genetic divide" between rich and poor.

23. Genetic Engineering: Detailed Protocol

23.1 Step-by-Step: Making Recombinant Insulin

1. Isolate the human insulin gene: the gene for human insulin (or its A and B chain coding sequences) is identified using the known amino acid sequence (reverse translation using the genetic code). Alternatively, the gene is obtained from a cDNA library (complementary DNA synthesised from human pancreatic mRNA by reverse transcriptase).

2. Prepare the vector: a plasmid (e.g., pBR322) is isolated from E. coli. The plasmid is cut with the same restriction enzyme(s) used to excise the insulin gene, creating complementary sticky ends.

3. Ligate: the insulin gene is mixed with the cut plasmid and DNA ligase, which joins the gene into the plasmid at the restriction site. The resulting recombinant plasmid contains the insulin gene.

4. Transform: the recombinant plasmid is introduced into E. coli cells by:

   • Heat shock: cells are made competent (treated with $\mathrm{CaCl_2}$ to make the membrane permeable), mixed with plasmid DNA, and heated to $42$ degrees C for 90 seconds (causes the membrane to become transiently permeable).
   • Electroporation: an electric pulse creates temporary pores in the cell membrane.

5. Select: transformed bacteria are grown on agar plates containing an antibiotic (e.g., ampicillin). Only bacteria that have taken up the plasmid (which carries an ampicillin resistance gene) survive.

6. Screen: to confirm that the plasmid contains the insulin gene (not just religated plasmid without the insert), colonies are screened by:

   • Blue-white screening (if using a plasmid with lacZ gene): colonies with the insert are white; colonies without the insert are blue.
   • Colony PCR: amplifying the insert region from bacterial colonies using primers flanking the cloning site.
   • Restriction digest analysis: isolating plasmid DNA and cutting with restriction enzymes to check for the correct insert size.

7. Culture and harvest: confirmed recombinant bacteria are grown in large fermenters. The bacteria express the insulin gene, producing proinsulin (or the A and B chains separately).

8. Purify: the insulin protein is extracted from the bacteria and purified by chromatography.

23.2 Advantages of Recombinant Human Insulin over Animal Insulin

Feature	Recombinant Human Insulin	Animal Insulin (pig/cow)
Amino acid sequence	Identical to human insulin	Slightly different (1--3 amino acid differences)
Allergic reactions	Rare (identical to human protein)	More common (immune system recognises as foreign)
Supply	Unlimited (bacteria grow rapidly)	Limited (requires slaughter of animals)
Consistency	Uniform product from batch to batch	Variable (depends on source animal)
Cost	Lower (once established)	Higher (animal farming costs)
Ethical concerns	Fewer (no animal slaughter)	Animal welfare concerns

24. Bioinformatics: Worked Examples

24.1 Calculating Pairwise Sequence Identity

Two DNA sequences are aligned:

Sequence A: 5'-ATG CCT AGG TCA GCT AGA TCC-3' Sequence B: 5'-ATG CCT AAG TCA GCA AGA TCC-3'

Alignment (vertical bars indicate matches):

ATG CCT A|GG| TCA GC|T| AGA TCC
ATG CCT A|AG| TCA GC|A| AGA TCC

Matches: 18 out of 21 positions match. Pairwise identity $= \frac{18}{21} = 85.7\%$.

The two sequences differ at positions 10 (G vs A) and 16 (T vs A). Both are transitions (purine $\leftrightarrow$ purine or pyrimidine $\leftrightarrow$ pyrimidine), which are more common than transversions (purine $\leftrightarrow$ pyrimidine).

24.2 Translating an Open Reading Frame

Given the DNA sequence: 5'-ATG CCA AGG TCA GCT AGA TCC TAA-3'

Translate in the correct reading frame:

Codon	Amino Acid
ATG	Met (start)
CCA	Pro
AGG	Arg
TCA	Ser
GCT	Ala
AGA	Arg
TCC	Ser
TAA	Stop

The protein is: Met-Pro-Arg-Ser-Ala-Arg-Ser (7 amino acids, 21 nucleotides of coding sequence plus 3 for the stop codon $= 24$ nucleotides).

28. Antibiotic Resistance: Detailed Analysis

28.1 Mechanisms of Resistance

Mechanism	Genetic Basis	Example
Enzymatic destruction	Plasmid-borne $\beta$-lactamase gene	ESBL-producing E. coli
Target modification	Mutations in penicillin-binding proteins	MRSA (mecA gene)
Reduced permeability	Mutations in porin proteins	Pseudomonas aeruginosa (carbapenem resistance)
Active efflux	Overexpression of efflux pump genes	E. coli (multidrug resistance)
Alternative pathway	Mutation in target enzyme	M. tuberculosis (rifampicin resistance)

28.2 Horizontal Gene Transfer of Resistance

Method	Description	Example
Conjugation	Cell-to-cell contact via pilus; plasmid transfer	R plasmid transferred between E. coli and Klebsiella
Transformation	Uptake of free DNA from environment	S. pneumoniae acquiring penicillin resistance
Transduction	Bacteriophage transfers bacterial DNA	Phage-mediated toxin gene transfer in C. diphtheriae

28.3 The Antibiotic Resistance Crisis

• At least 700,000 people die annually from drug-resistant infections worldwide (WHO, 2019).
• Some bacteria are now pan-resistant (resistant to all known antibiotics).
• Strategies: antibiotic stewardship, infection control, rapid diagnostics, new drug development, phage therapy.

29. Microbiome Applications in Biotechnology

29.1 The Human Microbiome

The human microbiome consists of approximately $10^{13}$--$10^{14}$ microorganisms (bacteria, archaea, fungi, viruses) residing on and in the human body. The gut microbiome alone contains approximately 3 million unique genes (150 times the human genome).

Body Site	Dominant Organisms	Functions
Large intestine	Bacteroidetes, Firmicutes, Actinobacteria	Fermentation of dietary fibre; vitamin K and B synthesis; immune modulation
Skin	Staphylococcus, Corynebacterium, Malassezia	Pathogen colonisation resistance; wound healing
Oral cavity	Streptococcus, Veillonella, Fusobacterium	Biofilm formation; pH regulation
Vagina	Lactobacillus spp.	Lactic acid production (low pH inhibits pathogens)

29.2 Faecal Microbiota Transplantation (FMT)

FMT involves transferring faecal material from a healthy donor to a patient to restore a healthy gut microbiome. It is most effective for treating recurrent Clostridium difficile infection (cure rate > 90%), which often develops after broad-spectrum antibiotic treatment destroys the normal gut microbiota.

Mechanism: the donor microbiota outcompetes C. difficile for nutrients and adhesion sites, produces antimicrobial substances, and restores colonisation resistance.

29.3 Probiotics and Prebiotics

• Probiotics: live microorganisms that confer a health benefit when consumed in adequate amounts (e.g., Lactobacillus rhamnosus GG for diarrhoea prevention; Bifidobacterium for immune support).
• Prebiotics: substrates that are selectively utilised by host microorganisms to confer a health benefit (e.g., inulin, fructo-oligosaccharides, galacto-oligosaccharides).
• Synbiotics: products combining probiotics and prebiotics.

30. Advanced Genetic Engineering Techniques

30.1 RNA Interference (RNAi)

RNAi is a natural gene regulation mechanism that has been exploited as a biotechnology tool:

1. Double-stranded RNA (dsRNA) complementary to the target mRNA is introduced into the cell.
2. The enzyme Dicer cleaves the dsRNA into small interfering RNAs (siRNAs), approximately 21--23 nucleotides long.
3. The siRNA is loaded into the RNA-induced silencing complex (RISC).
4. RISC uses the siRNA as a guide to find complementary mRNA and cleaves it, preventing translation.

Applications: gene knockdown in research; pest-resistant crops (e.g., GM papaya resistant to papaya ringspot virus); potential therapeutic applications (e.g., patisiran for hereditary transthyretin amyloidosis).

30.2 Induced Pluripotent Stem Cells (iPSCs)

iPSCs are adult somatic cells that have been reprogrammed to a pluripotent state by introducing four transcription factors (Oct4, Sox2, Klf4, c-Myc -- the "Yamanaka factors"). iPSCs can differentiate into any cell type, offering potential for:

• Disease modelling: creating patient-specific cell lines to study disease mechanisms.
• Drug testing: testing drug efficacy and toxicity on patient-specific cells.
• Regenerative medicine: generating replacement cells or tissues (e.g., dopamine neurons for Parkinson's disease, cardiomyocytes for heart repair).
• Gene therapy: correcting genetic defects in iPSCs and then differentiating them into the required cell type for transplantation.

30.3 Synthetic Biology

Synthetic biology involves designing and constructing new biological parts, devices, and systems, or redesigning existing natural biological systems:

Application	Description	Status
Synthetic genomes	Complete chemical synthesis of bacterial genomes (Mycoplasma mycoides JCVI-syn3.0, 473 genes)	Proof of concept (2010)
Genetic circuits	Engineered regulatory networks (toggle switches, oscillators, logic gates)	Research
Metabolic engineering	Engineering microorganisms to produce biofuels, pharmaceuticals, or chemicals	Commercial (artemisinin, 1,4-butanediol)
Biosensors	Engineered organisms that detect environmental pollutants or disease biomarkers	Research/clinical trials
Xenobiology	Using alternative nucleotides (XNA) or amino acids to create organisms with expanded genetic codes	Research

31. Environmental Biotechnology

31.1 Bioremediation Techniques

Technique	Description	Application
In situ bioremediation	Treatment at the contaminated site without excavation	Oil spill cleanup; groundwater decontamination
Ex situ bioremediation	Contaminated material is excavated and treated elsewhere	Soil washing; biopiles; bioreactors
Bioaugmentation	Adding specific microorganisms to enhance degradation	Pseudomonas for hydrocarbon degradation
Biostimulation	Adding nutrients or oxygen to stimulate native microorganisms	Adding nitrates and phosphates to oil-contaminated soil
Phytoremediation	Using plants to absorb, accumulate, or degrade pollutants	Sunflowers for uranium absorption; willow trees for organic pollutants

31.2 Biosensors

Biosensors use biological components to detect specific substances:

Component	Function	Example
Biological recognition element	Binds specifically to the target analyte	Enzyme (glucose oxidase for blood glucose); antibody; DNA probe; whole cell
Transducer	Converts the biological interaction into a measurable signal	Electrode (electrochemical); optical fibre (fluorescence); piezoelectric crystal
Detector	Amplifies and displays the signal	Digital readout; computer interface

Applications:

• Medical diagnostics: glucose monitors for diabetes (glucose oxidase electrode); pregnancy tests (monoclonal antibodies to hCG).
• Environmental monitoring: detecting pesticides, heavy metals, BOD (biochemical oxygen demand) in water.
• Food safety: detecting pathogens (e.g., Salmonella, E. coli O157) in food samples.
• Biodefence: detecting anthrax, smallpox, or other biological weapons.

31.3 Bioprocessing and Downstream Processing

After fermentation, the desired product must be extracted and purified:

Step	Purpose	Methods
Cell separation	Remove cells from fermentation broth	Centrifugation; filtration (microfiltration, ultrafiltration)
Cell disruption	Release intracellular products	High-pressure homogenisation; sonication; enzymatic lysis
Product recovery	Isolate the product from the broth	Precipitation (ammonium sulphate); liquid-liquid extraction
Purification	Remove impurities	Chromatography (affinity, ion exchange, size exclusion); electrophoresis
Polishing	Achieve final product quality	Ultrafiltration; crystallisation; lyophilisation (freeze-drying)

31.4 Scaling Up: From Lab to Industrial Fermenter

Factor	Lab Scale	Industrial Scale
Volume	< 10 L	10,000--500,000 L
Aeration	Shaking or simple sparging	Sterile air at controlled flow rate
Temperature control	Water bath or incubator	Jacketed vessel with cooling water
pH control	Manual or simple buffer	Automated acid/base addition
Sterilisation	Autoclave	Steam-in-place (SIP) at 121 degrees C for 30+ minutes
Monitoring	Manual sampling	Online probes (pH, dissolved $\mathrm{O_2}$, temperature, foam)

32. Genomics and Personalised Medicine

32.1 The Human Genome Project

The Human Genome Project (HGP, 1990--2003) sequenced the entire human genome:

• Approximately 3.2 billion base pairs.
• Approximately 20,000--25,000 protein-coding genes (far fewer than originally predicted).
• Only approximately 1.5% of the genome codes for proteins.
• Approximately 50% of the genome consists of repetitive sequences (transposons, LINEs, SINEs).
• Single nucleotide polymorphisms (SNPs) occur approximately every 300 base pairs; approximately 10 million common SNPs in the human population.

32.2 Pharmacogenomics

Pharmacogenomics uses genetic information to predict an individual's response to drugs:

Drug	Genetic Factor	Effect	Clinical Application
Warfarin (anticoagulant)	Variants in CYP2C9 and VKORC1 genes	Affects dose required; some individuals metabolise warfarin more slowly, increasing bleeding risk	Genotype-guided dosing improves safety
Abacavir (HIV drug)	HLA-B*57:01 allele	Increased risk of severe hypersensitivity reaction	Genetic testing before prescribing prevents adverse reactions
Codeine	CYP2D6 polymorphism	Poor metabolisers get no pain relief; ultra-rapid metabolisers may experience toxicity	Genetic testing guides opioid selection
Clopidogrel (antiplatelet)	CYP2C19 loss-of-function alleles	Reduced activation of prodrug; increased risk of cardiovascular events	Alternative antiplatelet drugs for poor metabolisers
Herceptin (breast cancer)	HER2 gene amplification	Drug is only effective in tumours with HER2 overexpression	HER2 testing selects patients who will benefit

32.3 Personalised Medicine: Benefits and Challenges

Benefits:

• More effective treatments (right drug, right dose, right patient).
• Fewer adverse drug reactions.
• Earlier disease detection (genetic screening for cancer susceptibility).
• Targeted therapies (e.g., imatinib for chronic myeloid leukaemia with BCR-ABL fusion gene).

Challenges:

• Cost: whole genome sequencing and genetic testing are expensive (though costs are falling rapidly).
• Data privacy: genetic information is highly personal; concerns about insurance discrimination and data security.
• Ethical issues: genetic testing may reveal unexpected findings (e.g., risk of untreatable diseases); consent and counselling are essential.
• Equity: personalised medicine may widen health inequalities if only available to wealthy individuals or countries.
• Interpretation: many genetic variants have uncertain clinical significance; distinguishing pathogenic from benign variants is challenging.

32.4 Bioinformatics Tools

Tool/Database	Purpose	URL
BLAST	Compare a DNA or protein sequence against databases to find similar sequences	blast.ncbi.nlm.nih.gov
Ensembl	Genome browser; annotation of genes, regulatory elements, variants	ensembl.org
OMIM	Catalogue of human genes and genetic disorders	omim.org
UniProt	Protein sequences, function, and structure information	uniprot.org
PDB	3D structures of proteins, nucleic acids, and complexes	rcsb.org
Gene Ontology	Standardised vocabulary for gene and protein function	geneontology.org

33. Tissue Culture and Micropropagation

33.1 Plant Tissue Culture

Plant tissue culture involves growing plant cells, tissues, or organs on an artificial nutrient medium under aseptic (sterile) conditions:

1. Explant selection: a small piece of plant tissue (leaf disc, stem segment, meristem) is taken from the parent plant.
2. Surface sterilisation: the explant is sterilised (e.g., with dilute bleach or ethanol) to remove surface contaminants.
3. Callus formation: the explant is placed on a nutrient medium containing auxin and cytokinin (plant growth regulators). The cells divide and form an undifferentiated mass of cells called a callus.
4. Organogenesis or somatic embryogenesis: by adjusting the ratio of auxin to cytokinin, the callus can be induced to form shoots (high cytokinin:auxin ratio) or roots (high auxin:cytokinin ratio).
5. Acclimatisation: plantlets are transferred to soil and gradually exposed to normal environmental conditions (lower humidity, higher light).

Applications:

• Mass propagation of elite varieties (orchids, bananas, strawberries).
• Production of disease-free plants (meristem culture: the meristem is virus-free because it has no vascular tissue).
• Conservation of endangered species (cryopreservation of plant tissue).
• Production of secondary metabolites (e.g., shikonin from Lithospermum for use in dyes and medicines).

33.2 Animal Cell Culture

Animal cells are grown in vitro for research, drug testing, and biotechnology:

Requirement	Description
Growth medium	Contains amino acids, vitamins, glucose, salts, and usually 5--10% foetal bovine serum (FBS, provides growth factors and hormones)
Incubator	37 degrees C; 5% $\mathrm{CO_2}$ (maintains pH of the medium via bicarbonate buffer system)
Sterile conditions	Laminar flow cabinet; antibiotics/antimycotics in medium
Substrate	Most animal cells are anchorage-dependent (must attach to a surface to divide); tissue culture flasks are coated with collagen or poly-lysine
Subculturing (passaging)	When cells reach confluence (cover the entire surface), they are detached using trypsin and transferred to a new flask

Cell line types:

• Primary cell cultures: derived directly from tissue; limited lifespan (senesce after approximately 50 divisions -- the Hayflick limit).
• Immortalised cell lines: have acquired mutations that bypass senescence; can divide indefinitely. Examples: HeLa cells (cervical cancer cells, derived from Henrietta Lacks in 1951); CHO cells (Chinese hamster ovary cells, used for recombinant protein production).

33.3 Hybridoma Technology (Monoclonal Antibody Production)

1. A mouse is immunised with the target antigen.
2. B cells (antibody-producing) are extracted from the mouse's spleen.
3. The B cells are fused with myeloma cells (immortal cancer cells) using polyethylene glycol (PEG) or electrofusion.
4. The resulting hybrid cells (hybridomas) are selected using HAT medium: only hybridomas survive (myeloma cells lack HGPRT enzyme and die; unfused B cells have limited lifespan and die).
5. Individual hybridoma cells are cloned (by limiting dilution) to produce monoclonal populations, each producing a single specific antibody.
6. The monoclonal antibodies are harvested from the culture medium (or from the ascites fluid of mice injected with the hybridoma).

Applications of monoclonal antibodies:

• Medical diagnosis: pregnancy tests (anti-hCG); detecting HIV, hepatitis, and other infections; blood typing.
• Therapy: trastuzumab (Herceptin) for HER2-positive breast cancer; rituximab for B-cell lymphoma; adalimumab (anti-TNF-$\alpha$) for rheumatoid arthritis.
• Research: identifying and locating specific proteins (immunofluorescence, Western blotting, IHC).
• Purification: affinity chromatography using antibody-coated columns.

34. Gene Therapy

34.1 Types of Gene Therapy

Type	Description	Advantages	Disadvantages
Somatic gene therapy	Correcting the gene in body (somatic) cells; changes are not inherited	Treats the individual; does not affect germ cells; more ethically acceptable	Does not prevent transmission to offspring; may require repeated treatment (if corrected cells are not stem cells)
Germ line gene therapy	Correcting the gene in sperm, eggs, or embryos; changes are inherited	Would permanently eliminate the disease from the family line	Ethically controversial; currently illegal in most countries; unknown long-term consequences; risk of off-target effects

34.2 Gene Therapy Methods

Method	Description	Example
Gene addition (viral vector)	A functional copy of the gene is inserted into the patient's cells using a viral vector (e.g., retrovirus, adenovirus, AAV)	Luxturna for inherited retinal dystrophy (AAV vector delivers RPE65 gene to retinal cells)
Gene addition (non-viral)	A functional gene is delivered using liposomes, nanoparticles, or naked DNA	Less immunogenic than viral vectors but less efficient
Gene editing (CRISPR-Cas9)	The defective gene is directly corrected in situ	Ex vivo editing of haematopoietic stem cells for sickle cell disease and $\beta$-thalassaemia (Casgevy, approved 2023)
RNA interference	Silencing a harmful gene using siRNA or shRNA	Patisiran for hereditary transthyretin amyloidosis

34.3 Successes and Challenges

Successes:

• Severe combined immunodeficiency (SCID): early gene therapy trials cured "bubble boys" by inserting a functional copy of the ADA gene into bone marrow cells.
• Sickle cell disease / $\beta$-thalassaemia: CRISPR-based therapy (Casgevy) approved in 2023; edits BCL11A enhancer to reactivate foetal haemoglobin (HbF), which does not sickle.
• Spinal muscular atrophy (SMA): Zolgensma delivers SMN1 gene using AAV9 vector; single-dose treatment, dramatic improvement in motor function.

Challenges:

• Immune response: the patient may mount an immune response against the viral vector (pre-existing immunity to adenovirus is common).
• Insertional mutagenesis: viral vectors may integrate near oncogenes, causing cancer (this occurred in early SCID trials; 5 of 20 patients developed leukaemia).
• Delivery: getting the gene to the right cells in sufficient numbers is difficult.
• Duration of effect: some vectors provide only transient expression (adenoviral vectors are not integrated; expression is lost as cells divide).
• Cost: gene therapies are extremely expensive (\approx \1$--$3.5 million per patient for single-dose treatments).

35. GMO Case Studies: Benefits and Risks

35.1 Golden Rice

• Problem: vitamin A deficiency (VAD) affects approximately 190 million children worldwide, causing blindness and increased mortality.
• Solution: rice engineered to produce $\beta$-carotene (precursor to vitamin A) in the endosperm, giving the rice a golden colour.
• Genes involved: phytoene synthase (from daffodil or maize) and phytoene desaturase/crt I (from bacterium Erwinia uredovora).
• Benefit: could prevent 1--2 million deaths per year from VAD.
• Concerns: not yet widely adopted; cultural acceptance; cross-contamination with non-GM rice; intellectual property issues (patents held by multiple companies); efficacy (bioavailability of $\beta$-carotene from Golden Rice is debated).

35.2 Bt Crops

• Genes: genes from Bacillus thuringiensis (Bt) encoding insecticidal crystal (Cry) proteins.
• Mechanism: Cry proteins are toxic to specific insect pests (e.g., European corn borer, cotton bollworm) when ingested. The protein is activated in the insect gut, forming pores in the gut epithelium, causing sepsis and death.
• Benefits: reduced use of chemical insecticides; increased yield; specific toxicity (does not harm non-target organisms, including humans and most beneficial insects).
• Concerns: evolution of Bt-resistant pests (resistance management strategies include planting non-Bt refuges); potential impact on non-target insects (e.g., monarch butterfly controversy); gene flow to wild relatives.

35.3 Herbicide-Tolerant Crops

• Genes: genes encoding enzymes that detoxify herbicides (e.g., EPSPS enzyme from Agrobacterium confers glyphosate tolerance in Roundup Ready soybeans).
• Benefits: simplified weed management; allows no-till farming (reduces soil erosion); increased yield.
• Concerns: development of herbicide-resistant weeds ("superweeds"); increased herbicide use; gene flow to wild relatives; corporate control of seed supply.

35.4 Ethical Considerations of GM Crops

Argument For	Argument Against
Feeding a growing world population (9.7 billion by 2050)	Long-term ecological effects are unknown
Reducing pesticide use (Bt crops)	Corporate control of food supply (patented seeds)
Improving nutritional quality (Golden Rice)	"Playing God" / unnatural
Reducing food waste (delayed-ripening tomatoes, non-browning apples)	Potential for allergens from transgenes
Drought- and disease-resistant crops for climate change adaptation	Cross-contamination with non-GM crops; loss of biodiversity

36. Cloning: Organismal Cloning Techniques

36.1 Plant Cloning by Cuttings

1. Take a cutting from a parent plant (include a node, where leaves and buds are attached).
2. Remove most leaves (reduce water loss).
3. Dip the cut end in rooting powder (contains auxin to stimulate root growth).
4. Plant the cutting in moist compost; cover with a plastic bag to maintain humidity.
5. The cutting develops roots and grows into a genetically identical clone.

Advantages: simple, quick, cheap. Disadvantages: limited to species that root easily; genetic uniformity increases vulnerability to disease.

36.2 Plant Cloning by Tissue Culture (Micropropagation)

(See Section 33.1 for detailed protocol.)

36.3 Animal Cloning: Reproductive Cloning

Somatic Cell Nuclear Transfer (SCNT):

1. A somatic (body) cell is taken from the animal to be cloned (e.g., an udder cell from Dolly the sheep).
2. The nucleus is extracted from the somatic cell.
3. An enucleated egg cell (an egg cell with its nucleus removed) is prepared from a donor female.
4. The somatic cell nucleus is inserted into the enucleated egg cell by electrofusion or microinjection.
5. The reconstructed egg is stimulated (by an electric shock or chemical treatment) to begin dividing.
6. The embryo is cultured in vitro for a few days.
7. The embryo is implanted into the uterus of a surrogate mother.
8. The surrogate gives birth to a clone of the original animal.

Dolly the sheep (1996): the first mammal cloned from an adult somatic cell. 277 embryos were created; only 29 implanted; only one live birth (Dolly). Dolly developed arthritis and lung disease at a relatively young age, and was euthanised at age 6 (normal sheep lifespan is 11--12 years). This raised concerns about premature ageing in clones (telomere shortening).

36.4 Therapeutic Cloning

Similar to SCNT, but the embryo is used to produce embryonic stem cells (ESCs) rather than being implanted into a surrogate. The ESCs are genetically identical to the patient, so they could be used for:

• Growing replacement tissues or organs for transplantation (no rejection).
• Studying genetic diseases in patient-specific cell lines.
• Drug testing on patient-specific cells.

36.5 Natural Cloning

Organism	Method	Example
Bacteria	Binary fission (asexual reproduction)	E. coli divides every 20 minutes under optimal conditions
Fungi	Spore production; fragmentation	Mushrooms release spores; bread mould (Mucor) spreads by fragmentation
Plants	Runners (strawberry), tubers (potato), bulbs (daffodil), vegetative propagation	Gardeners take cuttings, divide bulbs, or separate runners
Animals	Parthenogenesis (some insects, reptiles, fish): egg develops without fertilisation	Aphids reproduce parthenogenetically in summer; Komodo dragons can reproduce by parthenogenesis

37. DNA Fingerprinting: Detailed Analysis

37.1 Minisatellites vs Microsatellites (STRs)

Feature	Minisatellites (VNTRs)	Microsatellites (STRs)
Repeat unit length	10--100 base pairs	2--6 base pairs
Total length	0.5--30 kb	100--400 bp
Number in genome	Thousands	Hundreds of thousands
Mutation rate	High ($\approx 10^{-4}$ per generation)	Lower ($\approx 10^{-3}$ per generation)
Method of analysis	Southern blotting (radioactive probes)	PCR and capillary electrophoresis
Current use	Largely replaced by STRs	Standard in forensic DNA profiling

37.2 DNA Fingerprinting in Forensics

Crime scene investigation:

1. DNA is extracted from biological evidence at the crime scene (blood, semen, saliva, hair follicles, skin cells).
2. DNA is extracted from the suspect.
3. STR loci are amplified by PCR using fluorescently labelled primers.
4. PCR products are separated by capillary electrophoresis.
5. Fragment sizes are compared between the crime scene sample and the suspect.

Interpreting results:

• Match: the probability of a random match at all 10+ STR loci is extremely low ($< 1$ in a billion).
• No match: the suspect is excluded.
• Partial match: may indicate a close relative of the suspect (family members share approximately 50% of STR alleles).

37.3 Paternity Testing

DNA fingerprinting can determine paternity by comparing the child's DNA profile with the alleged father's and the mother's:

• The child must have inherited one allele at each locus from the mother and one from the father.
• If the alleged father does not carry the paternal allele at any locus, he is excluded as the biological father.
• If the alleged father carries the paternal allele at all loci tested, the probability of paternity is calculated (typically > 99.9% if the man is the biological father).

38. Bioinformatics: Analysing Biological Data

38.1 Sequence Alignment

Sequence alignment compares two or more DNA, RNA, or protein sequences to identify regions of similarity:

Type	Description	Use
Pairwise alignment	Comparing two sequences	Finding conserved regions between two species; identifying orthologous genes
Multiple sequence alignment	Comparing three or more sequences simultaneously	Identifying conserved domains; constructing phylogenetic trees; identifying functional motifs

Scoring alignments:

• Match: +1 (identical bases at the same position).
• Mismatch: -1 (different bases).
• Gap: -2 (insertion or deletion).

A higher score indicates greater similarity.

38.2 BLAST Search: Worked Example

A researcher has identified a gene sequence from an unknown bacterium:

5'-ATGGCTAGCTGA-3'

They run a BLASTn (nucleotide BLAST) search against the NCBI database. The top hit is:

5'-ATGGCTAGCTGA-3' (100% identity, E-value $= 10^{-12}$, from E. coli -- lacZ gene fragment)

Interpretation:

• % identity: 100% -- every base matches.
• E-value: $10^{-12}$ -- the probability of getting this good a match by chance is 1 in $10^{12}$. An E-value $< 0.05$ is considered significant.
• Bit score: a measure of alignment quality (higher = better). Typically > 50 is significant.

The unknown bacterium likely carries a gene similar to E. coli lacZ ($\beta$-galactosidase).

38.3 Phylogenetic Trees

Phylogenetic trees show the evolutionary relationships between species:

1. Molecular data (DNA or protein sequences) are used to construct the tree.
2. The number of differences between sequences is proportional to the time since the species diverged from a common ancestor.
3. The tree is rooted (the root represents the common ancestor).
4. Branch lengths are proportional to the number of sequence changes (molecular clock).

Example tree:

                    ┌── Human
              ┌─────┤
          ┌───┤     └── Chimpanzee
          │   └──────────── Gorilla
Common ancestor
          │   ┌──────────── Orangutan
          └───┤
              └──────────── Gibbon

Humans and chimpanzees are most closely related (fewest sequence differences), followed by gorillas, then orangutans and gibbons.

39. Golden Rice and Biofortification

39.1 The Vitamin A Deficiency Problem

• Vitamin A deficiency (VAD) affects approximately 190 million preschool children worldwide.
• VAD causes night blindness, xerophthalmia (dry eyes), and increased susceptibility to infections.
• VAD is most common in populations that rely heavily on rice as a staple food (rice contains no $\beta$-carotene/provitamin A).

39.2 Golden Rice: Genetic Engineering Solution

Golden rice is a genetically engineered variety of rice that produces $\beta$-carotene (provitamin A) in the endosperm:

Gene	Source	Enzyme Produced	Step in Pathway
psy (phytoene synthase)	Daffodil (Narcissus pseudonarcissus)	Phytoene synthase	Geranylgeranyl diphosphate $\to$ phytoene
crtI (phytoene desaturase)	Soil bacterium (Pantoea ananatis, formerly Erwinia uredovora)	Phytoene desaturase	Phytoene $\to$ lycopene (multiple desaturation steps)
lcyl (lycopene $\beta$-cyclase)	Daffodil	Lycopene $\beta$-cyclase	Lycopene $\to$ $\beta$-carotene

39.3 Biofortification Approaches

Approach	Description	Examples
Conventional breeding	Select and cross varieties with higher nutrient content	Iron-rich beans; zinc-rich wheat
Genetic engineering	Introduce genes that increase nutrient content or bioavailability	Golden rice ($\beta$-carotene); iron-biofortified cassava (ferritin gene from soybean)
Agronomic fortification	Apply mineral fertilisers to soil to increase crop mineral content	Selenium-biofortified wheat; iodine-biofortified cereals

40. Biofuels

40.1 Types of Biofuels

Biofuel Type	Source	Process	Energy Density	Advantages	Disadvantages
Bioethanol (1st generation)	Sugar cane, corn, wheat	Yeast ferments sugars to ethanol; distilled to increase concentration	~23 MJ/kg (lower than petrol at ~45 MJ/kg)	Renewable; carbon-neutral (CO2 released = CO2 absorbed during growth)	Competes with food production; land use change (deforestation); lower energy density
Biodiesel (1st generation)	Vegetable oils (rapeseed, soybean, palm), waste cooking oil	Transesterification of triglycerides with methanol	~37 MJ/kg	Biodegradable; can use waste oil	Lower energy density than diesel; higher viscosity; cold flow problems
Cellulosic ethanol (2nd generation)	Lignocellulosic biomass (wood chips, straw, grasses)	Pretreatment + enzymatic hydrolysis + fermentation	~23 MJ/kg	Does not compete with food; uses agricultural waste	Expensive; complex pretreatment required; not yet commercially viable at scale
Biogas (anaerobic digestion)	Animal manure, food waste, sewage sludge	Anaerobic bacteria break down organic matter; produce methane (~60%) + CO2 (~40%)	~21 MJ/m3	Uses waste materials; produces fertiliser as by-product	Lower energy density; requires large digesters; methane leaks potent greenhouse gas

40.2 Bioethanol Production from Yeast

Step	Process	Conditions
1. Milling	Grain is ground to increase surface area	--
2. Gelatinisation	Starch granules are heated in water; they swell and burst	80--90$\degree\mathrm{C}$
3. Hydrolysis	Enzymes (amylase) break down starch to maltose and glucose	55--65$\degree\mathrm{C}$; pH 5--6
4. Fermentation	Yeast (Saccharomyces cerevisiae) anaerobically respires glucose to ethanol + CO2	30--35$\degree\mathrm{C}$; anaerobic; pH 4--5
5. Distillation	Ethanol is separated from the fermentation mixture (ethanol boils at 78$\degree\mathrm{C}$, water at 100$\degree\mathrm{C}$)	Fractional distillation

41. Tissue Culture and Micropropagation

41.1 Plant Tissue Culture

Step	Description
1. Explant selection	A small piece of plant tissue (meristem, leaf, stem) is taken from the parent plant (sterile conditions)
2. Surface sterilisation	Explant is sterilised (e.g., bleach, ethanol) to remove surface microorganisms
3. Callus formation	Explant is placed on agar medium containing auxin and cytokinin; cells divide to form an undifferentiated mass of cells (callus)
4. Organogenesis	The medium is adjusted (different auxin:cytokinin ratio) to stimulate shoot or root formation
5. Acclimatisation	Plantlets are transferred from sterile conditions to soil (gradual exposure to normal environment)

41.2 Growth Substances in Tissue Culture

Substance	Role
Auxin (e.g., 2,4-D, IAA, NAA)	Stimulates root formation; at high concentration relative to cytokinin, promotes callus formation
Cytokinin (e.g., BAP, kinetin, zeatin)	Stimulates shoot formation; at high concentration relative to auxin, promotes shoot development
Auxin:Cytokinin ratio	High auxin:cytokinin $\to$ roots; Low auxin:cytokinin $\to$ shoots; Equal $\to$ callus
Sucrose	Carbon source (since callus cells cannot photosynthesise)
Agar	Solid medium to support the tissue
Vitamins and minerals	Essential for growth (Murashige and Skoog medium is standard)

41.3 Applications

Application	Description
Cloning elite plants	Produces thousands of genetically identical copies of a plant with desirable traits (disease resistance, high yield)
Conservation of rare species	Micropropagation of endangered plant species for reintroduction to the wild
Disease-free planting material	Meristem culture produces virus-free plants (meristems have low viral titre)
Genetic engineering	Tissue culture is used to regenerate whole plants from genetically modified cells
Secondary metabolite production	Plant cell cultures can produce valuable compounds (e.g., taxol from yew, shikonin from Lithospermum)

42. Genetic Modification of Animals

42.1 Methods

Method	Description	Example
Microinjection	DNA injected directly into the pronucleus of a fertilised egg	Transgenic mice expressing human genes for disease research
Retroviral vectors	Retroviruses carry the transgene and insert it into the host genome	Gene therapy vectors
CRISPR-Cas9	Guide RNA directs Cas9 nuclease to a specific DNA sequence; creates a double-strand break; DNA repair machinery inserts the new gene (or knocks out a gene)	Gene editing in livestock (e.g., hornless cattle); disease-resistant pigs; correcting genetic disorders
Somatic cell nuclear transfer (SCNT)	Nucleus from a genetically modified somatic cell is transferred into an enucleated egg; the egg develops into a cloned organism	Dolly the sheep (first cloned mammal, 1996)

42.2 Applications of Transgenic Animals

Application	Description	Example
Pharmaceutical production	Transgenic animals produce therapeutic proteins in their milk, eggs, or urine	Transgenic goats producing antithrombin III (ATryn) in their milk; used to prevent blood clots
Xenotransplantation	Transgenic animal organs used for human transplantation	Pigs engineered to lack $\alpha$-1,3-galactosyltransferase (reduces hyperacute rejection); pigs expressing human complement regulatory proteins
Disease models	Animals engineered to carry human disease genes for research	Oncomouse (carries human oncogene; develops cancer); Huntington's disease mice; Alzheimer's mice
Agriculture	Animals with improved traits	Fast-growing salmon (AquaBounty; engineered with growth hormone gene); disease-resistant livestock

43. Cloning Animals

43.1 Reproductive Cloning (Somatic Cell Nuclear Transfer)

Step	Description
1	A somatic (body) cell is taken from the animal to be cloned
2	The nucleus is extracted from this somatic cell
3	An enucleated egg cell is obtained (egg cell with its nucleus removed)
4	The somatic cell nucleus is inserted into the enucleated egg (by microinjection or electrofusion)
5	An electric shock stimulates the egg to divide (activates the egg; mimics fertilisation)
6	The embryo develops in vitro for a few days
7	The embryo is implanted into a surrogate mother
8	The surrogate gives birth to the cloned animal (genetically identical to the somatic cell donor)

43.2 Advantages and Disadvantages of Animal Cloning

Advantages	Disadvantages
Produces genetically identical animals for research (controls variables)	Low success rate (~1--5% of implanted embryos survive to birth)
Preserves valuable genetics (elite breeding stock, endangered species)	Cloned animals often have health problems (large offspring syndrome, premature ageing, immune defects)
Potential for therapeutic cloning (patient-specific stem cells)	Ethical concerns (especially about human cloning)
Reproduces transgenic animals efficiently	Reduced genetic diversity

44. Ethical Issues in Biotechnology

44.1 GM Crops: Arguments For and Against

Arguments For	Arguments Against
Increased crop yields (feed growing population)	Potential unknown long-term health effects of GM food
Reduced pesticide use (Bt crops produce their own insecticide)	Development of resistant pests ("superweeds", "superbugs")
Enhanced nutritional content (Golden Rice; biofortified crops)	Corporate control of food supply (patented seeds; farmers must buy new seed each year)
Drought-resistant and salt-tolerant varieties (climate change adaptation)	Gene flow to wild relatives (transgenes could spread to non-GM crops or wild plants)
Reduced post-harvest losses (delayed ripening, disease resistance)	Ethical concerns about "playing God" with nature
Lower food prices (increased supply)	Loss of biodiversity (monocultures of GM crops)

44.2 Genetic Testing: Ethical Considerations

Issue	Description
Genetic discrimination	Employers or insurance companies could use genetic information to discriminate against individuals
Psychological impact	Knowing one's genetic risk for a late-onset disease (e.g., Huntington's) can cause anxiety, depression
Informed consent	Individuals must understand the implications of genetic testing before agreeing
Privacy and confidentiality	Who has access to genetic information? How is it stored? Can it be shared without consent?
Reproductive choices	Prenatal genetic testing raises questions about selective termination (abortion based on genetic traits)
Incidental findings	Genetic testing may reveal unexpected information (e.g., non-paternity, risk of unrelated diseases)

45. Gene Therapy

45.1 Somatic vs Germ-Line Gene Therapy

Type	Description	Ethical Status
Somatic gene therapy	Genes are introduced into body cells (somatic cells) of the patient; changes are NOT passed to offspring	Generally accepted (treats disease in the individual)
Germ-line gene therapy	Genes are introduced into germ cells (sperm, egg, zygote); changes ARE passed to offspring	Currently banned in most countries (ethical concerns; unknown long-term consequences; "designer babies")

45.2 Methods of Delivering Genes

Vector	Description	Advantages	Disadvantages
Viral vectors (retroviruses, lentiviruses, adenoviruses, AAV)	Modified virus carries the therapeutic gene into target cells	Efficient delivery; some integrate into host genome (permanent)	Risk of immune response; risk of insertional mutagenesis (virus may disrupt a tumour suppressor gene); limited cargo capacity
Liposomes	Lipid vesicles containing the therapeutic gene fuse with the cell membrane	No viral risk; low immunogenicity	Lower efficiency; transient expression (DNA does not integrate)
Naked DNA	Direct injection of plasmid DNA	Simple; safe	Very low efficiency
CRISPR-Cas9	Direct gene editing (correct the mutation in situ)	Precise; permanent correction	Off-target effects; delivery challenges; ethical concerns

45.3 Gene Therapy Successes and Challenges

Disease	Gene Therapy Status	Details
Severe combined immunodeficiency (SCID-X1)	Early success; later setbacks	First successful gene therapy (2000); 10 of 11 patients cured; however, 5 developed leukaemia (insertional mutagenesis activating oncogenes)
ADA-SCID	Approved (Strimvelis)	Ex vivo gene therapy; patient's bone marrow cells are modified and reinfused
Spinal muscular atrophy (SMA)	Approved (Zolgensma)	AAV vector delivers SMN1 gene; single-dose treatment; very expensive (~$2 million)
Cystic fibrosis	Clinical trials ongoing	Liposome and viral delivery to airway epithelial cells; limited success so far (delivery barriers)
Haemophilia	Clinical trials ongoing	AAV vectors delivering factor VIII or IX genes; promising early results

46. Environmental Biotechnology

46.1 Bioremediation

Bioremediation uses living organisms (usually microorganisms) to clean up polluted environments:

Type	Description	Example
In situ bioremediation	Contaminants are treated in place (at the site of pollution)	Oil spill cleanup: naturally occurring oil-degrading bacteria (Pseudomonas, Alcanivorax) break down hydrocarbons; adding nutrients (nitrogen, phosphorus) stimulates their growth
Ex situ bioremediation	Contaminated material is removed and treated elsewhere	Soil excavation and composting; biopiles; landfarming
Phytoremediation	Plants are used to absorb, accumulate, or degrade pollutants	Helianthus (sunflower) absorbs heavy metals (lead, uranium) from soil; Thlaspi caerulescens (alpine pennycress) hyperaccumulates zinc and cadmium
Mycoremediation	Fungi are used to break down pollutants	White-rot fungi (Phanerochaete chrysosporium) produce lignin peroxidase enzymes that degrade organic pollutants (PCBs, PAHs, dioxins)

46.2 Wastewater Treatment

Stage	Process	What Is Removed
Primary treatment	Physical: screening (removes large debris); sedimentation (sludge settles out)	Large solids; ~60% of suspended solids
Secondary treatment	Biological: activated sludge (aerobic bacteria break down organic matter); trickling filter	Dissolved organic matter; ~90% of organic matter removed
Tertiary treatment	Chemical/physical: sand filtration; UV disinfection; nutrient removal (nitrification/denitrification)	Remaining pathogens; phosphates and nitrates (prevent eutrophication); heavy metals

47. Bioinformatics and Genomics

47.1 Applications of Bioinformatics

Application	Description
Personalised medicine	Analysing a patient's genome to tailor drug choice and dosage (pharmacogenomics)
Drug discovery	Identifying potential drug targets by comparing pathogen and human genomes
Evolutionary biology	Comparing genomes across species to reconstruct evolutionary relationships
Forensics	DNA fingerprinting for criminal identification and paternity testing
Agriculture	Identifying genes for disease resistance, drought tolerance, and nutritional quality in crops
Epidemiology	Tracking the spread of infectious diseases by sequencing pathogen genomes (e.g., tracking COVID-19 variants)

47.2 DNA Profiling (DNA Fingerprinting)

Step	Description
1. DNA extraction	DNA is extracted from a biological sample (blood, saliva, hair root)
2. PCR amplification	Specific regions of DNA are amplified (e.g., short tandem repeats, STRs)
3. Gel electrophoresis	DNA fragments are separated by size on an agarose gel; smaller fragments move further
4. Comparison	The pattern of bands is compared between samples (e.g., suspect vs crime scene)

Feature	Description
STRs (short tandem repeats)	Short sequences (2--6 base pairs) that are repeated in tandem; the number of repeats varies between individuals; highly polymorphic (many different alleles in the population)
Probability of match	The probability of two unrelated individuals having the same DNA profile is extremely low (< 1 in a billion if enough loci are tested)
Uses	Criminal identification; paternity testing; identifying disaster victims; immigration disputes

48. Induced Pluripotent Stem Cells (iPSCs)

48.1 What Are iPSCs?

iPSCs are adult somatic cells that have been reprogrammed to a pluripotent state (similar to embryonic stem cells) by introducing specific transcription factors.

48.2 Yamanaka Factors

Factor	Gene	Role
Oct4	POU5F1	Maintains pluripotency; activates pluripotency genes
Sox2	SOX2	Maintains pluripotency; works with Oct4
Klf4	KLF4	Involved in cell proliferation; helps repress differentiation genes
c-Myc	MYC	Promotes cell division; opens chromatin (makes genes more accessible)

48.3 Advantages of iPSCs over Embryonic Stem Cells

Advantage	Description
No ethical controversy	Does not require destruction of embryos
Patient-specific	Can be derived from the patient's own cells; no immune rejection
Disease modelling	iPSCs from patients with genetic diseases can be differentiated into the affected cell type for study
Drug screening	Patient-derived cells can be used to test drug responses in vitro

48.4 Limitations

Limitation	Description
Risk of mutations	Reprogramming process can introduce genetic abnormalities
Tumour risk	c-Myc is an oncogene; iPSC-derived cells may form teratomas
Not fully equivalent	iPSCs may retain some epigenetic memory of their cell of origin
Efficiency	Low efficiency (only ~0.1--1% of cells are successfully reprogrammed)

49. RNA Interference (RNAi)

49.1 What Is RNAi?

RNA interference is a natural mechanism for regulating gene expression by silencing specific genes. It uses small RNA molecules to target and destroy mRNA molecules.

49.2 Mechanism

Step	What Happens
1	Double-stranded RNA (dsRNA) is introduced into the cell or produced endogenously
2	The enzyme Dicer cleaves the dsRNA into small interfering RNAs (siRNAs, ~21--23 nucleotides)
3	The siRNA duplex is unwound; one strand (the guide strand) is loaded into the RISC complex (RNA-induced silencing complex)
4	The guide strand binds to a complementary mRNA sequence by base pairing
5	RISC cleaves the target mRNA; the mRNA is degraded; the gene is effectively silenced (no protein produced)

49.3 Applications

Application	Description
Functional genomics	Knocking down specific genes to study their function
Therapeutics	siRNA drugs to silence disease-causing genes (e.g., patisiran for hereditary transthyretin amyloidosis)
Agriculture	RNAi sprays to protect crops from viruses (e.g., against Colorado potato beetle)
Pest control	Developing RNAi-based insecticides that silence essential genes in pest species

50. Synthetic Biology

50.1 What Is Synthetic Biology?

Synthetic biology applies engineering principles to biology to design and construct new biological parts, devices, and systems that do not exist in the natural world, or to redesign existing biological systems for useful purposes.

50.2 Key Achievements

Achievement	Description
Synthetic genome	Craig Venter's team created a synthetic bacterial chromosome (M. mycoides JCVI-syn1.0) and transplanted it into a recipient cell; the synthetic genome took over the cell and the cell reproduced
Minimal genome	The smallest genome that supports life (473 genes in Mycoplasma genitalium); essential genes were identified by systematically knocking out genes one at a time
BioBricks	Standardised, interchangeable DNA parts (promoters, ribosome binding sites, coding sequences, terminators) that can be assembled into genetic circuits
Genetic circuits	Synthetic gene networks that perform logic functions (AND gates, NOT gates, oscillators) -- the basis of biological computing

50.3 Applications

Application	Description
Biofuels	Engineering bacteria/algae to produce ethanol, butanol, and biodiesel more efficiently
Biosensors	Living cells that detect environmental pollutants (arsenic, mercury) and produce a measurable output (fluorescence, colour change)
Drug production	Engineering microorganisms to produce complex drugs (artemisinin for malaria; taxol for cancer; opioids) more cheaply
Gene drives	Engineering genes that spread rapidly through wild populations (e.g., to make malaria mosquitoes sterile; controversial ecological risks)
Cell-free systems	Using cell-free transcription-translation systems (extracted from bacteria) to produce proteins without living cells

51. Bioinformatics

51.1 What Is Bioinformatics?

Bioinformatics is the application of computing and statistical techniques to the analysis of biological data, especially large datasets from genome sequencing projects.

51.2 Key Tools and Databases

Tool/Database	Purpose
BLAST (Basic Local Alignment Search Tool)	Compares a DNA or protein sequence against all known sequences in a database; identifies similar sequences and organisms
GenBank	Comprehensive public database of DNA sequences (maintained by NCBI)
Ensembl	Genome browser for vertebrate genomes; annotations of genes, proteins, and regulatory elements
UniProt	Database of protein sequences and functional information
PubMed	Database of scientific literature; searchable by keyword, author, or gene name
Clustal Omega	Multiple sequence alignment tool; aligns three or more sequences to identify conserved regions
PhyML / MEGA	Software for constructing phylogenetic trees from sequence data

51.3 Applications of Bioinformatics

Application	Description
Comparative genomics	Comparing genomes across species to identify genes responsible for specific traits or diseases
Protein structure prediction	Using AI (e.g., AlphaFold) to predict protein 3D structures from amino acid sequences
Drug target identification	Identifying pathogen proteins that could be targeted by new drugs
Evolutionary studies	Constructing phylogenetic trees; estimating divergence times
Personalised medicine	Analysing an individual's genome to predict disease risk and drug response

52. Tissue Culture and Micropropagation

52.1 Principles

Tissue culture is the growth of cells, tissues, or organs in an artificial nutrient medium under sterile conditions.

52.2 Steps in Micropropagation

Step	Description
1. Selection	A small piece of tissue (explant) is taken from the parent plant (e.g., from the shoot tip or leaf bud)
2. Sterilisation	The explant is sterilised (e.g., using dilute bleach or ethanol) to remove surface contaminants (bacteria, fungi)
3. Culture	The explant is placed on a sterile agar gel containing nutrients, sucrose, vitamins, and plant growth substances (auxins and cytokinins)
4. Callus formation	The explant divides by mitosis to form an undifferentiated mass of cells called a callus
5. Differentiation	By adjusting the ratio of auxin to cytokinin, the callus can be induced to develop shoots and roots
6. Acclimatisation	The plantlets are transferred from the agar to soil; they must be gradually hardened off (reducing humidity) before being moved to normal greenhouse conditions

52.3 Advantages and Disadvantages

Advantages	Disadvantages
Produces large numbers of identical plants (clones) very quickly	Requires sterile conditions (expensive equipment)
Disease-free stock (meristem tissue culture produces virus-free plants)	All plants are genetically identical (no genetic variation; vulnerable to the same diseases)
Can propagate plants that do not produce viable seeds (e.g., bananas)	Somaclonal variation may occur (mutations during tissue culture)
Year-round production (independent of seasons)	Not all species respond well to tissue culture

53. Golden Rice and Biofortification

53.1 What Is Golden Rice?

Golden rice is a genetically modified variety of rice that produces beta-carotene (a precursor of vitamin A) in the endosperm of the rice grain. It was developed to address vitamin A deficiency (VAD) in populations where rice is the staple food.

53.2 How It Was Made

Step	Description
Genes added	Two genes from daffodil (psy) and one gene from a soil bacterium (crtI) were inserted into the rice genome; these genes enable the rice endosperm to produce beta-carotene (which normal rice cannot do)
Mechanism	The added genes encode enzymes in the carotenoid biosynthesis pathway: phytoene synthase and phytoene desaturase
Result	The rice grains have a characteristic golden-yellow colour due to the beta-carotene content

53.3 Biofortification

Feature	Description
What it is	Increasing the nutritional value of crops through genetic modification or conventional breeding
Examples	Golden rice (beta-carotene); iron-rich beans; zinc-enhanced wheat; vitamin-enriched sweet potato (orange-fleshed sweet potato, achieved by conventional breeding)
Advantages	Addresses micronutrient deficiencies in populations that rely on a limited number of staple crops; does not require changes to diet or supplementation programmes

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