Genetics Engineering
Genetic engineering is an umbrella term that can cover a wide range of ways of
changing the genetic material -- the DNA code -- in a living organism. This code
contains all the information, stored in a long chain chemical molecule, which
determines the nature of the organism. Apart from identical twins, genetic
make-up is unique to each individual. Individual genes are particular sections
of this chain, spaced out along it, which determine the characteristics and
functions of our body. Defects of individual genes can cause a malfunction in
the metabolism of the body, and are the roots of many "genetic" diseases. In
a sense, man has been using genetic engineering for thousands of years. We
weren't changing DNA molecules directly, but we were guiding the selection of
genes. For example the domestication of plants and animals. Recombinant DNA
technology is the newest form of genetic engineering, which involves the
manipulation of DNA on the molecular level. This is a totally new process based
on the science of molecular biology, a relatively new science only forty years
old. It represents a major increase in our ability to improve life. But a
negative aspect is that it changes the forms of life we know of, possibly
damaging our environment It has been known for some time that genetic
information can be transferred between micro-organisms. This is process it done
via plasmids (small circular rings of DNA) or phages (bacterial viruses). Both
of these are termed vectors, this is because of their ability to move genetic
material. In general this is limited to simpler species of bacteria.
nevertheless, this can restriction can be overcome with the use of genetic
engineering because it allows the introduction of any gene. While genetic
engineering is beginning to be used to produce enzymes, the technology itself
also depends on the harnessing of enzymes, which are available in nature. In the
early 1970s Herbert Boyer, working at the University of California Health

Science Centre in San Francisco, and Stanley Cohen at Stanford University found
that it was possible to insert into bacteria genes they had removed from other
bacteria. First they learned the trick of breaking down the DNA of a donor
organism into manageable fragments. Second, they discovered how to place such
genes into a vector, which they used to ferry the fragments of DNA into
recipient bacteria. Once inside its new host, a transported gene divided as the
cell divided, leading to a clone of cells, each containing exact copies of the
gene. This technique became known as gene cloning, and was followed by the
selection of recipient cells containing the desired gene. The enzymes used for
cleaving out the DNA pieces act in a highly specific way. Genes can, therefore,
be removed and transferred from one organism to another with extraordinary
precision. Such manoeuvres contrast sharply with the much less predictable gene
transfers that occur in nature. By mobilising pieces of DNA in this way
(including copies of human genes), genetic engineers are now fabricating
genetically modified microbes for a wide range of applications in industry,
medicine and agriculture. The underlying idea of transferring genes between
cells is quickly explained. However the actual practice is an extremely
complicated process. The scale of the problem can be gauged from the
astronomical numbers involved: the DNA of even the simplest bacterium contains

4,800,00 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, each
containing one or just a few genes. These enzymes cut DNA in very precise ways.

They recognise particular stretches of bases (termed recognition sequences) and
snip each strand of the double helix at a particular place. Whenever the
recognition 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, they
always produce the same set of fragments. The cuts produce pieces of double
helix with short stretches of single stranded DNA at each end. These are know as
sticky ends. If the enzyme is allowed to act for a limited time, it may not have
a chance to attack all the recognition sequences in the chain. This will result
in longer fragments. As in natural DNA replication, bases have an inherent
propensity 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 to
re-associate with AATT. Genetic engineers use another type of enzyme, DNA ligase,
to make the union permanent. This is the key