issue 217 - March 1991
ALL ILLUSTRATIONS: JIM NEEDLE
GAMBLING WITH GENES
|A GUIDE TO GENETIC ENGINEERING|
Genetic engineers are transforming the features, characteristics
and abilities of living things in an unprecedented way. And these
changes will continue to be inherited for generations.
NI gives an account of how it happens.
A cell is the smallest part of a living thing that can exist alone. Plants or animals can be made up of one or more cells. Each is adapted to its individual tasks: muscle cells are elastic so that we can move our limbs. Red blood cells carry oxygen through the blood. And plant cells have a rigid cell wall to make the plant firm. Cells manufacture more cells. And all of them, whether in animals or plants, are organized and work in basically the same way. Their control centre is a nucleus which is surrounded by a thin membrane and is often found in the centre of the cell. It directs the cell’s activities.
2. Messages and messengers
Cells are made from complex non-living chemicals called biochemicals. We eat three of these as food – proteins, carbohydrates and fats – to provide a chemical supply for the processes that take place in our body. Another biochemical activates them – called deoxribonucleic acid or DNA. It lives in the cell’s nucleus and controls the way that new cells are made and old ones are repaired. It is the cell’s information carrier and conveys and alters heredity, as well as containing enough information to build not just another cell but a complete human body. Another kind of nucleic acid, ribonucleic acid or RNA acts as the messenger between DNA and the rest of the cell.
3. Rungs and ladders
Like many biochemicals, DNA is built from thousands of tiny units, each containing atoms of carbon, oxygen and hydrogen. Its structure is a double helix – like a very long spiral step ladder with thousands of millions of rungs. The sides of the ladder are made from long chains of units called ‘nucleotides’. And the rungs are composed of four units called bases. These are always found in the same pairs on each strand of the helix and the way the bases are ordered along the DNA forms a code which carries all the information needed to build new cells. Joined end to end the DNA helices in a human being would reach to the moon and back nearly 8,000 times.
4. Practical proteins
DNA relies on proteins to reproduce cells. These exist in all living things. And there are thousands of different kinds of protein, each composed of various combinations of approximately 20 amino acids, and each performing a different function. Some proteins digest food. Others help make new cell materials. Yet others make the skin tough and flexible. Inside cells, proteins help make new cell materials and build the cells themselves. The special qualities of each individual protein – whether it belongs to a leaf or a root or a muscle depends on the arrangement of the amino acid of which it is composed. And this is determined by information stored in the DNA’s chemical code.
5. Chemical sentences
Scientists can read the base units – or ‘rungs’ – of a DNA molecule according to their sequence. A section of DNA molecule which has the complete code for a single protein is called a gene. There are thousands of genes in every DNA molecule, linked together to form even longer strands called chromosomes. These are usually found in the cell nucleus and occur in pairs: there are 23 pairs of chromosomes in human cells. Each gene is like a chemical sentence: the amino acids are the words, the chromosome is a chapter of the book and the sum of the chromosomes are the final book, containing enough information to build not just another cell but a complete reproduction of the entire organism from which it comes.
Living things pass on their characteristics to their offspring through DNA – the messenger in the chromosomes. By adding or taking away sections of DNA the characteristics inherited by an animal’s offspring can be manipulated. The process of transferring genes from one organism to another is a bit like editing a written text, using scissors and glue to ‘cut and paste’. The ‘scissors and glue’ of genetic engineering are enzymes that enable biologists to snip genes out of DNA molecules and stick them into the DNA of another micro-organism. This way scientists have produced various useful proteins including genetically-engineered insulin, growth hormones and the antiviral protein called interferon. The technology holds potential for diagnosing and treating genetic ailments in humans, for improving food production and for performing other useful tasks. But it could also do enormous harm because it alters the structure of organisms in ways we can’t necessarily predict. Once released into the environment we can’t control these as we don’t know what they will do.
The way that genetic-engineering is used depends on who controls the technology. At present a handful of multinational companies in the North control it and their priority is to boost their profits rather than to serve human need. While the technology could be useful in developing pest-resistant crops which might increase agricultural production, chemical companies are creating herbicide-resistant seeds so that they can increase their herbicide sales. They have developed hybrid seed which does not breed true and so forces farmers to buy more seed from them every year. And other companies are developing artificial substitutes for crops that Third World farmers depend on, which could devastate Third World economies. These decisions are too important to be left up to multinational companies. They affect everyone. This technology is so powerful that we must use it wisely. Which means finding out what the world needs and acting accordingly.