The first antibiotic to be manufactured was penicillin, which is produced mostly by P. notatum and P. chrysogenum. The impact of this discovery was enormous because penicillin was active against all staphylococcal infections, yet was virtually non-toxic to the patient. It is still considered the most important antibiotic today. Antibiotics are also widely used to stimulate the growth of livestock in agriculture. It can be added to animal feed, killing micro-organisms including pathogens as well as promoting protein synthesis in the body.
Ever since the cause of diabetes was discovered to be a shortage of the hormone insulin, sufferers have been given insulin from the pancreases of slaughtered sheep and cattle. Occasionally there have been damaging side effects due to small differences in the chemical composition of insulin from different species. The procedure for this is very complicated because insulin has two polypeptide chains. Firstly, two artificial DNA molecules that code for the two appropriate amino acid chains are synthesised. These are introduced into separate bacteria by the process for synthetic genes. After growing large quantities of the bacteria in fermenters, they are split open, the chains purified and then chemically combined in an oxidation reaction. They then behave exactly the same as natural human insulin and insulin is now used in routine clinical practice throughout the world.
There is a 1 in 5000 chance that too little of the human growth hormone (GH), in extreme cases causes pituitary dwarfism. Growth hormones from animals are not effective in humans, but injections of GH can overcome this problem, although they are in very short supply and are very expensive considering that they can only be obtained from pituitary glands of human cadavers. Trials of GH produced by genetic engineering (using DNA) began in the USA and then spread to Britain in the late 1980s.
The mammalian growth hormone is made in a similar way to insulin and has both clinical and agricultural uses. Injecting a cow with a bovine growth hormone can increase milk production by as much as 25%, whereas beef cattle show a 10-15% increase in body mass.
Vaccines have contributed enormously to the fight against infectious diseases. They are usually produced from viruses raised in cell cultures or in laboratory animals, which are both very expensive procedures. It is the protein coats of viruses that are antigenic, stimulating us to produce antibodies. Scientists can genetically engineer the bacterium E. coli so that it synthesises proteins of the kind that are found in the coat of the hepatitis virus. The result is a cheap vaccine against hepatitis that less economically developed countries can afford.
In agriculture single cell protein (SCP) is used as a new food source. Protein is derived from the large-scale growth of micro-organisms (e.g. bacteria, yeast, fungi and algae) and can be put to use as animal feed. There are lots of advantages for this: they occupy less room than normal crops and animals, they grow much more rapidly and they can grow on a wide variety of cheap or waste products of agriculture. Sadly, there are even more disadvantages. These include: agricultural surpluses becoming common in developed countries, developing countries not being able to afford the investment in equipment and training, an increase in production and reduction of the price of competitive animal feed additives, and a rise in oil prices in the late 1970s due to SCP production being energy-intensive.
In conclusion, DNA synthesis can increase the yields from livestock and crops using SCP or growth hormones, meaning that more may be sold on the market, increasing income for farmers. This is important, but the impact of the discovery of DNA has been far more consequential in medicine, where it helps to produce vaccines, insulin shots and antibiotics that save millions of lives and improve peoples' quality of life.
Bibliography:
A New Introduction to Human Biology, by Bill Indge
New Scientist Magazine, 21st August 1999