Genetic engineering is an umbrella term that can cover a wide range of ways ofchanging the genetic material — the DNA code — in a living organism. This codecontains all the information, stored in a long chain chemical molecule, whichdetermines the nature of the organism. Apart from identical twins, geneticmake-up is unique to each individual. Individual genes are particular sectionsof this chain, spaced out along it, which determine the characteristics andfunctions of our body. Defects of individual genes can cause a malfunction inthe metabolism of the body, and are the roots of many genetic diseases. Ina sense, man has been using genetic engineering for thousands of years.Order now
Weweren’t changing DNA molecules directly, but we were guiding the selection ofgenes. For example the domestication of plants and animals. Recombinant DNAtechnology is the newest form of genetic engineering, which involves themanipulation of DNA on the molecular level. This is a totally new process basedon the science of molecular biology, a relatively new science only forty yearsold. It represents a major increase in our ability to improve life.
But anegative aspect is that it changes the forms of life we know of, possiblydamaging our environment It has been known for some time that geneticinformation can be transferred between micro-organisms. This is process it donevia plasmids (small circular rings of DNA) or phages (bacterial viruses). Bothof these are termed vectors, this is because of their ability to move geneticmaterial. In general this is limited to simpler species of bacteria. nevertheless, this can restriction can be overcome with the use of geneticengineering because it allows the introduction of any gene.
While geneticengineering is beginning to be used to produce enzymes, the technology itselfalso depends on the harnessing of enzymes, which are available in nature. In theearly 1970s Herbert Boyer, working at the University of California HealthScience Centre in San Francisco, and Stanley Cohen at Stanford University foundthat it was possible to insert into bacteria genes they had removed from otherbacteria. First they learned the trick of breaking down the DNA of a donororganism into manageable fragments. Second, they discovered how to place suchgenes into a vector, which they used to ferry the fragments of DNA intorecipient bacteria. Once inside its new host, a transported gene divided as thecell divided, leading to a clone of cells, each containing exact copies of thegene.
This technique became known as gene cloning, and was followed by theselection of recipient cells containing the desired gene. The enzymes used forcleaving out the DNA pieces act in a highly specific way. Genes can, therefore,be removed and transferred from one organism to another with extraordinaryprecision. Such manoeuvres contrast sharply with the much less predictable genetransfers that occur in nature.
By mobilising pieces of DNA in this way(including copies of human genes), genetic engineers are now fabricatinggenetically modified microbes for a wide range of applications in industry,medicine and agriculture. The underlying idea of transferring genes betweencells is quickly explained. However the actual practice is an extremelycomplicated process. The scale of the problem can be gauged from theastronomical numbers involved: the DNA of even the simplest bacterium contains4,800,00 pairs of bases. But there is only one copy of each gene in each cell.
First, restriction enzymes are used to snip the DNA into smaller pieces, eachcontaining one or just a few genes. These enzymes cut DNA in very precise ways. They recognise particular stretches of bases (termed recognition sequences) andsnip each strand of the double helix at a particular place. Whenever therecognition sequence appears in the long DNA chain, the enzyme makes a cut.
Whenever the same enzymes are used to break up a certain piece of DNA, theyalways produce the same set of fragments. The cuts produce pieces of doublehelix with short stretches of single stranded DNA at each end. These are know assticky ends. If the enzyme is allowed to act for a limited time, it may not havea chance to attack all the recognition sequences in the chain.
This will resultin longer fragments. As in natural DNA replication, bases have an inherentpropensity to join up with their partners A with T, for example, and G with C. So too with sticky ends. For example, the sequence TTAA will tend tore-associate with AATT. Genetic engineers use another type .