Topic 21: Biotechnology and genetic modification

Microorganisms work tirelessly for us, turning sugar into alcohol, breaking down stains in our washing and even producing life-saving medicines. Biotechnology harnesses these tiny living factories, while genetic modification lets us transfer useful genes from one organism to another. This topic explores how we put microbes and genes to work.

Why microorganisms are so useful

Bacteria and fungi are ideal for industry for several reasons:

• They reproduce very quickly, so large quantities can be grown in a short time.
• They have few ethical concerns compared with using animals or plants.
• They can make complex molecules and can be grown using waste materials.
• Their genes can be changed relatively easily by genetic engineering.

Two especially important uses involve yeast, a single-celled fungus. In baking, yeast respires sugar and releases carbon dioxide, which makes bread dough rise. In brewing, yeast carries out anaerobic respiration (fermentation), converting sugar into alcohol and carbon dioxide.

Industrial enzymes

Enzymes extracted from microorganisms are widely used because they speed up reactions at relatively low temperatures, saving energy. Examples include:

• Biological washing powders contain proteases and lipases that break down protein and fat stains, working effectively at lower temperatures than ordinary detergents.
• Pectinase is used to increase the yield and clarity of fruit juice.
• Lactase is used to produce lactose-free milk for people who cannot digest lactose.

Enzymes are often used in an immobilised form so they can be reused, making processes cheaper.

Fermenters and growing microorganisms

To grow microorganisms on a large scale, industry uses a fermenter — a large vessel in which conditions are carefully controlled to give the highest yield. Key conditions and how they are managed include:

• Temperature — a water jacket cools the contents because respiration releases heat, keeping enzymes working at their optimum.
• pH — monitored and adjusted to suit the organism.
• Oxygen — sterile air is bubbled in for aerobic processes.
• Nutrients — a supply of food is added for growth.
• Stirring — paddles keep the contents mixed so temperature and nutrients are evenly spread.

Everything is kept sterile so that no unwanted microbes contaminate the product.

Genetic modification

Genetic modification (genetic engineering) means changing the genetic material of an organism by removing, changing or inserting genes from another organism. A key example is producing human insulin from bacteria:

• The human insulin gene is cut from human DNA using restriction enzymes.
• A bacterial plasmid is cut with the same enzyme, and the gene is joined in using ligase enzymes.
• The plasmid is returned to a bacterium, which then makes human insulin as it multiplies.

Insulin made this way is identical to human insulin and avoids using animal sources. Crops can also be modified — for example to resist insects, tolerate herbicides or contain extra vitamins. Benefits include higher yields and better nutrition, while concerns include possible effects on wild species and uncertainty about long-term impacts.