Applications of
Molecular Biology

A transgenic organism (or genetically modified organism, GMO) is any organism whose genetic material has been artificially altered using gene technology. This includes: insertion of one or more new genes from another species, duplication of existing genes, deletion of genes, or modification of gene activity. The key word is artificial — the change was made deliberately in a laboratory, not by natural processes.

Categories of GMOs

The process of making GMOs is different for each category — plant transformation uses Agrobacterium or gene guns; animal transgenesis uses microinjection or nuclear transfer; bacterial transformation uses heat shock or electroporation.

Gene technology encompasses four core activities: (1) understanding how genes are expressed, (2) taking advantage of natural genetic variation, (3) modifying genes in the lab, and (4) transferring genes to new host organisms. Topics 2–4 gave you the individual tools (restriction enzymes, vectors, PCR, transformation, etc.). Topic 5 shows you what those tools are used to build.

Two Methods for Delivering DNA into Plants

• Indirect: Agrobacterium-mediated transformation — uses the soil bacterium Agrobacterium tumefaciens as a natural DNA delivery vehicle (see Section 3).
• Direct: Biolistics (gene gun / microprojectile bombardment) — tiny gold or tungsten particles coated with DNA are physically shot into plant cells at high speed. Brute force.

Agrobacterium tumefaciens is a soil bacterium that naturally infects wounded plants and transfers a piece of its own DNA (called T-DNA) into the plant cell's genome. In nature, this causes crown gall disease (tumours). Scientists hijack this system by replacing the tumour-causing genes in the T-DNA with their gene of interest — turning Agrobacterium into a gene delivery vehicle.

The Strategy (Step by Step)

1. Clone an E. coli origin of replication into the Ti plasmid (so it can be manipulated in bacteria).
2. Replace the tumour-causing genes in the T-DNA region with your gene of interest (keeping the left and right border sequences intact — these are needed for transfer).
3. Introduce the engineered Ti plasmid back into Agrobacterium.
4. Infect plant cells in tissue culture with the engineered Agrobacterium.
5. The T-DNA (now carrying your gene) integrates into the plant's chromosomal DNA.
6. Regenerate whole plants from the transformed cells using plant tissue culture.

Bacillus thuringiensis (Bt) is a soil bacterium that produces a protein toxin called delta-endotoxin, encoded by the Cry gene. This toxin is lethal to specific insect pests — it attacks the insect gut lining and stops the insect from feeding. Bt has been used as a biological insecticide since 1938.

Scientists cloned the Cry gene from Bt and inserted it into crop plant genomes using Agrobacterium tumefaciens. The resulting Bt crops (maize, cotton, potato, soybean — produced from 1996 onwards) produce the delta-endotoxin in all their tissues, making them inherently resistant to insect pests without external pesticide spraying.

Advantages of Bt Crops

• Only insects attacking the crop are poisoned — environmentally targeted.
• All plant tissues are protected, including roots (which sprayed pesticides cannot reach).
• The toxin is biodegradable — does not accumulate in the food chain.
• Reduces the need for chemical pesticide application.

Disadvantages of Bt Crops

• Non-target insects (pollinators like bees, butterflies) may also be affected.
• Insect pest populations can develop resistance to the Bt toxin over time.
• Pollen carrying the Cry gene could spread to wild relatives via cross-pollination.
• The technology is expensive, limiting access for small-scale farmers.
• Herbicides and other pesticides may still be needed for non-insect pests.

Enviropig

Traditional pigs cannot digest phytate phosphorus in grain feed, so undigested phosphorus passes into their waste and pollutes waterways. The Enviropig carries a transgene combining mouse and E. coli DNA that produces the enzyme phytase in its salivary glands. Phytase breaks down phytate in the stomach, allowing the pig to absorb phosphorus. Result: up to 65% less phosphorus in waste.

Spider Goats

Spider silk is 5x stronger than steel and 3x stronger than Kevlar, but spiders are carnivores and cannot be farmed. Scientists isolated the spider silk protein gene from the golden orb weaver (Nephila clavipes) and inserted it (with mammary gland-specific regulatory sequences) into goat cells. Female transgenic goats secrete spider silk protein in their milk, which is purified and extruded into silk thread. Applications: surgical sutures, artificial ligaments, lightweight body armour, biodegradable fishing line.

GM Salmon (AquAdvantage)

AquAdvantage salmon carry a growth hormone gene from Chinook salmon linked to a promoter from ocean pout (a cold-water fish). This causes the salmon to produce growth hormone year-round instead of only in warm months, reaching market size in ~18 months instead of ~3 years.

Pharming (pharmaceutical + farming) is the use of genetically engineered animals or plants to produce pharmaceutical proteins. Transgenic cattle, sheep, goats, chickens, rabbits, and pigs have been engineered to produce human therapeutic proteins — typically secreted in their milk, eggs, or blood.

Examples: goats producing human antithrombin (anti-clotting protein) in milk; rabbits producing human C1 esterase inhibitor; chickens producing human interferon in eggs. The advantage over bacterial expression is that animal cells can perform complex post-translational modifications (glycosylation, folding) that bacteria cannot.

Recombinant protein production is the process of cloning a human (or other) gene into an expression vector, transforming it into a host cell, and having the host cell produce the encoded protein at scale. This is how most modern biopharmaceuticals are manufactured.

The General Pipeline

1. Isolate the gene encoding the desired protein (e.g., human insulin gene).
2. Clone the gene into an expression vector (a vector with a strong promoter to drive high-level transcription).
3. Transform the vector into a host cell (E. coli, yeast, or mammalian cells).
4. Grow the host cells in large fermentation tanks (scale-up).
5. The host cells produce the recombinant protein.
6. Extract and purify the protein from the cell culture.
7. Formulate the purified protein into a pharmaceutical product.

Insulin was discovered by Banting and Best in 1921. It is a peptide hormone produced by the pancreas that regulates blood glucose levels. Diabetes patients either cannot produce insulin (Type 1) or cannot respond to it properly (Type 2). Before genetic engineering, insulin was extracted from pig and cow pancreases — expensive, limited supply, and sometimes caused allergic reactions.

In 1978, Genentech produced the first recombinant human insulin by cloning the human insulin gene into E. coli. By 1982, recombinant insulin (Humulin) became the first genetically engineered drug approved for human use.

The Hepatitis B vaccine is a recombinant subunit vaccine. Instead of using killed or attenuated virus, the vaccine contains only the viral surface antigen protein (HBsAg), produced by recombinant DNA technology in yeast cells (Saccharomyces cerevisiae). This is safer than using actual virus because no viral DNA is present — there is zero risk of infection from the vaccine.

Note the parallel with insulin production — same pipeline (clone gene → transform host → express protein → purify), but using yeast instead of E. coli because the HBsAg protein requires glycosylation (a post-translational modification that bacteria cannot perform).

Benefits

• Crops: Enhanced nutrition, increased yields, pest/disease/herbicide resistance, reduced spoilage, drought tolerance.
• Animals: Increased productivity, disease resistance, better feed efficiency, reduced environmental impact (Enviropig).
• Environment: Reduced pesticide use, soil/water conservation, bioremediation, biodegradable products.
• Medicine: Recombinant drugs (insulin, growth hormone, clotting factors), safer vaccines, gene therapy.
• Society: Increased food security for growing global population.

Concerns

• Safety: Potential allergens, unknown long-term health effects, antibiotic resistance marker transfer.
• Environment: Transgene escape via cross-pollination, effects on non-target organisms, biodiversity loss.
• Access/IP: Corporate domination of food supply (e.g., Monsanto), developing country dependence, biopiracy.
• Ethics: Tampering with nature, mixing genes across species, animal welfare, religious/cultural objections.
• Labelling: Not mandatory in all countries; mixing GM and non-GM products confounds labelling.

In Australia, GM food is regulated by Food Standards Australia New Zealand (FSANZ) and research is overseen by the Office of the Gene Technology Regulator (OGTR).

Agrobacterium vs Biolistics

Bacterial vs Yeast vs Mammalian Expression Systems