Biotechnology in Medicine and Agriculture

Core Concepts

Recombinant DNA products in medicine

The first and most famous product of genetic engineering is human insulin. Before recombinant technology, people with diabetes used insulin extracted from pig and cattle pancreases; supply was limited, and some people developed allergic reactions to the slightly different animal protein. The recombinant approach (approved for human use in 1982, a commonly taught date): isolate the human insulin gene, insert it into a plasmid, transform bacteria or yeast, grow the cells in fermentation tanks, and purify the secreted insulin. The product is identical to human insulin.

The same strategy produces human growth hormone, erythropoietin (for anemia), blood-clotting factors, and tissue plasminogen activator (tPA, used to dissolve blood clots). The pattern to remember: human gene → plasmid → host cell → fermentation → purified protein.

Engineered vaccines work differently. A subunit vaccine uses only a piece of a pathogen. For hepatitis B, the gene for the virus's surface antigen is put into yeast; the yeast makes the protein; the purified protein is the vaccine. Because no whole virus is involved, it cannot cause the disease it prevents.

Gene therapy

Gene therapy treats disease by adding a working copy of a gene to a person's cells. Ex vivo ("outside the living body") therapy removes the patient's cells — for example, blood or bone-marrow stem cells — inserts the corrected gene, and returns them. In vivo ("in the living body") therapy delivers the gene directly into the patient, usually packaged in a viral or non-viral vector.

The idea is simple, but delivery is hard: the immune system attacks viral vectors, genes must reach the right cells, and insertion into the wrong chromosomal location can disrupt other genes. Gene therapy remains an active, carefully regulated field rather than a routine cure.

Molecular diagnostics

Biotechnology also reads DNA. PCR makes millions of copies of a specific DNA segment, so a tiny sample — a drop of blood, a cheek swab — is enough to test. DNA probes are short, labeled pieces of single-stranded DNA that bind only to a matching sequence, lighting up when a particular gene or pathogen is present. DNA microarrays carry thousands of probes on one slide, measuring the expression of thousands of genes at once — useful for classifying cancers and guiding treatment.

Agricultural biotechnology

• Herbicide-tolerant crops. Soybeans and other crops engineered to resist glyphosate-type herbicides let farmers control weeds without killing the crop.
• Insect-resistant (Bt) crops. A gene from the bacterium Bacillus thuringiensis makes the plant produce a protein toxic to certain insect pests (such as corn borers) but not to humans or most other organisms. Bt corn and cotton reduce the need for sprayed insecticides.
• Golden rice. Engineered to make beta-carotene, the pigment our bodies convert into vitamin A, to help reduce vitamin A deficiency where rice is a staple food.
• The Flavr Savr tomato was the first genetically modified food approved for sale (1994, commonly taught); a modified gene slowed ripening so tomatoes could ripen on the vine and still survive shipping.
• Transgenic animals. Goats have been engineered to secrete therapeutic human proteins in their milk; knock-out mice, with a specific gene disabled, are standard tools for studying what genes do; Dolly, the sheep cloned from an adult cell in 1996 (commonly taught), showed that a specialized cell's nucleus could direct development of a whole new individual.

Regulation and the public debate

In the United States, engineered products are overseen by several agencies — the FDA (foods and drugs), the EPA (plants that produce pesticides), and the USDA (crops). Public concerns center on food safety and allergenicity, gene flow from engineered crops to wild relatives, labeling, and seed patents. Scientists generally assess products case by case: the technique matters less than the properties of the specific product.

Common Confusions