Biotechnology.

For thousands of years people have quietly put living things to work — yeast to raise bread and brew, bacteria to set milk into yoghurt. Today we go much further: we can cut a single human gene out of our DNA, paste it into a bacterium, and grow tonnes of pure human insulin. That power — engineering life itself — is biotechnology.

1 · What biotechnology is

Biotechnology is the use of living organisms (or parts of them — cells, enzymes, genes) to make useful products or to carry out useful processes for humans. It spans two eras.

• Traditional biotechnology — using whole microbes, often by fermentation, without altering their genes: yeast raises bread and ferments sugars into alcohol (beer, wine); lactic-acid bacteria (e.g. Lactobacillus) turn milk into yoghurt and cheese; microbes also make vinegar, soy sauce and antibiotics like penicillin.
• Modern biotechnology — based on genetic engineering: we deliberately change an organism's DNA, moving genes between species to give cells brand-new abilities (such as a bacterium making a human hormone).

2 · Genetic engineering — the big idea

Genetic engineering is the deliberate alteration of an organism's genetic material — usually by taking a gene from one organism and inserting it into another. When that gene is joined into the DNA of a different organism, the result is recombinant DNA ("recombined" DNA, because pieces from two sources are combined). An organism carrying foreign DNA is described as transgenic or genetically modified (GM).

The whole technology rests on three molecular tools, each of which you must be able to name and explain:

3 · Restriction enzymes — molecular scissors

A restriction enzyme recognises a short, specific sequence of bases (the recognition site, often 4–6 base pairs) and cuts the DNA only there. For example, the enzyme EcoRI always cuts at the sequence G A A T T C.

Crucially, many restriction enzymes make a staggered cut — they snip the two strands a few bases apart. This leaves short, single-stranded overhangs called sticky ends.

4 · Plasmids — the vectors

A vector is anything used to carry the gene into the host cell. The commonest is a plasmid — a small, circular piece of DNA found naturally in bacteria, separate from the main chromosome. Plasmids are ideal vectors because they are small, circular, replicate independently, and can be taken back up by bacteria. (Some viruses are also used as vectors.)

5 · DNA ligase — the glue

Once the gene's sticky ends have base-paired with the plasmid's sticky ends, the join is only loosely held. The enzyme DNA ligase then forms the permanent bonds (it seals the sugar–phosphate backbones), locking the gene into the plasmid. The product is a recombinant plasmid — a plasmid now carrying the foreign gene.

6 · Making recombinant DNA — the full procedure

Putting the tools together, the standard way to clone a gene (here, the human insulin gene) into a bacterium runs in clear steps:

1. Isolate the gene. Cut the wanted gene (e.g. the insulin gene) out of human DNA using a restriction enzyme, producing sticky ends.
2. Open the vector. Cut a bacterial plasmid open with the same restriction enzyme, so it has matching sticky ends.
3. Insert. Mix gene and plasmid; their complementary sticky ends base-pair and the gene slots in.
4. Seal. DNA ligase joins the backbones, forming the recombinant plasmid.
5. Transform. Put the recombinant plasmids back into host bacteria (e.g. E. coli); cells that take up a plasmid are transformed.
6. Clone & harvest. The bacteria multiply, copying the plasmid (and the gene) into millions of cells — a gene clone — and each cell now reads the gene and makes the human protein, which is then purified.

7 · Producing insulin & other human proteins

The most famous success of genetic engineering is human insulin for treating diabetes. Before genetic engineering, insulin was extracted from the pancreases of slaughtered pigs and cattle — it was scarce, expensive, and slightly different from human insulin, so it could cause reactions.

Now the human insulin gene is inserted into E. coli (or yeast) by the recombinant-DNA method above. The transformed microbes are grown in huge fermenters, each one churning out genuine human insulin, which is then purified. The product is identical to natural human insulin, made in unlimited amounts, with no animals needed.

8 · PCR — copying DNA a billion times

Often we have only a tiny trace of DNA — a smear at a crime scene, a single gene. The polymerase chain reaction (PCR) is a fast way to make millions of copies of a specific piece of DNA in a test tube — "amplifying" it. It needs the DNA sample, primers (short DNA pieces that mark where to start), free nucleotides, and a heat-stable enzyme, Taq DNA polymerase. The reaction is a repeated cycle of three temperature steps:

1. Denaturation (~95 °C) — high heat breaks the hydrogen bonds and separates the two DNA strands (unzips the double helix).
2. Annealing (~55 °C) — cooling lets the short primers bind to their complementary sequences at each end of the target.
3. Extension (~72 °C) — Taq polymerase adds nucleotides from each primer, building a new complementary strand and copying the DNA.

9 · Gene cloning & its applications

Gene cloning means making many identical copies of a gene (as the transformed bacteria multiply, or by PCR). Genetic engineering and cloning have transformed medicine, agriculture and forensics:

• Pharmaceuticals — bacteria/yeast mass-produce insulin, growth hormone, clotting factors and vaccines (e.g. the hepatitis-B vaccine is made by engineered yeast).
• GM crops (genetically modified crops) — useful genes are added to plants: Bt cotton/maize carry a bacterial gene that makes them pest-resistant; others are herbicide-tolerant, drought-tolerant, or enriched — like Golden Rice, engineered to make vitamin A.
• Gene therapy — a healthy gene is delivered into a patient's cells to correct a faulty gene that causes a genetic disease (such as cystic fibrosis or some immune disorders).
• DNA fingerprinting (DNA profiling) — everyone's DNA pattern is unique; comparing DNA profiles is used in forensics (matching a suspect to crime-scene DNA), paternity tests and identification.

10 · Ethical & safety issues

This power raises real concerns, which examiners expect you to mention briefly:

• Safety of GM food — possible allergies or unknown long-term effects.
• Environmental risk — engineered genes could escape into wild plants; pests may evolve resistance; loss of biodiversity.
• Ethics of gene therapy — especially altering genes that pass to offspring; fears of "designer babies".
• Privacy — misuse of an individual's DNA/genetic information.