Genetics Essay Research Paper GENETIC ENGINEERING

Genetics Essay, Research Paper

GENETIC ENGINEERING

“career of the future”

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 principle of genetic engineering the use of two types of enzyme to cut out one

piece of DNA and then to attach it to another piece. The genetic engineer’s toolkit now

contains several hundred different restriction enzymes. Each is a precision instrument for

fragmenting DNA in a particular way. Some recognise different base sequences; others

recognise the same sequence but snip at a different point within or next to the sequence.

Ferrying DNA to a new home Once a piece of DNA has been broken up into a mixture of

fragments, these can be separated into different sized pieces. The next stage is to insert a

particular DNA fragment into a vector. Often this is a plasmid, a selfreplicating circular

piece of DNA that can become incorporated in the bacterial nucleus and later become

detached, carrying genes with it. Plasmids seem to have evolved as a natural mechanism

for moving genes around among bacteria.

To insert a DNA fragment into a vector, the genetic engineer first splits open the

plasmid by adding the same restriction enzyme that was used to release the DNA

fragment from the DNA of the donor organism. This creates sticky ends complementary

to those on the fragment to be transplanted. The fragment thus fits neatly into the gap in

the vector DNA, where it is firmly annealed by DNA ligase.

Next, the plasmid is allowed to infect a bacterium, in which it can replicate. Once

inside, the vector and thus the foreign gene replicates every time the cell divides. As

bacteria divide about once every 20 minutes, gene cloning can lead to a billionfold

increase in the number of copies of a particular gene within 10 hours or so. The

bacterium simply treats it and replicates it as part of its own DNA.

Not all the countless cells in a culture of bacteria become infected when a vector

is added. One method of distinguishing those that do contain the vector is to incorporate

into it a gene that confers resistance to a particular antibiotic. When the bacteria are

cultured later, that antibiotic is included in the nutrient medium to inhibit any non

resistant organisms. Only bacteria that have taken up the vector (and thus the resistance

gene) are able to grow. A similar trick distinguishes bacteria carrying the vector plus a

new gene from unwanted ones containing the unaltered vector.

By using a variety of restriction enzymes to cut up DNA into manageable pieces,

and then cloning these sequences, it is possible to create a DNA library a collection of

sequences carrying all the genetic information in a particular organism. But much of this

information is not expressed at any particular moment. Genetic engineers are usually

interested only in the genes that are actually functioning at any one time for example,

one responsible for producing a specific enzyme. The DNA that codes for hereditary

messages specifying current activities of this sort is much smaller in quantity than the

total DNA in a cell. This information is to be found in messenger RNA. An enzyme

called reverse transcriptase allows its messages to be translated into DNA. This copy

DNA (cDNA) is then cloned into bacteria, giving a library, much smaller than that of a

cell’s total DNA, that will certainly contain the desired gene. But this still leaves the final

challenge of locating the specific bacteria containing the spliced gene. One method is to

spread the bacteria infected with the vector onto a nutrient medium, on which each

individual cell can spawn millions of progeny and thus appear as a visible colony. The

genetic engineer also needs to know the amino acid sequence of the protein coded by the

gene. By following the genetic code, a corresponding stretch of RNA can now be

synthesised chemically. During the synthesis, radioactive atoms are incorporated into the

RNA, making a gene probe.

The next step is to make, on special filter paper, a replica of the plate with the

colonies of the cloned bacteria. Treated with caustic soda, the bacteria burst open and

release their DNA, which is also broken into single strands that stick to the filter. The

gene probe is now added. If the correct sequence is present, the probe will pair

tenaciously with it. The filter is now washed to remove the unbound probe, and placed

over a piece of x-ray film. When developed, the film reveals the location of the

radioactivity as a black spot. The corresponding colony on the original plate thus

contains the bacteria carrying the required gene.

The applications of genetic engineering are vast, probably the most well known is

gene therapy in the medical world. It involves the introduction of a gene into somatic

cells and enablement of its products to alleviate a disorder caused by the loss or

malfunctioning of a vital gene product. Involving the latest DNA technology, it is the

most rapidly advancing form of molecular medicine, which is concerned with the cause

of disease at a molecular level. The scope for gene therapy has increased over in the last

few years with the possibility of a therapeutic gene for diseases such as cancer, AIDS,

cystic fibrosis, and even neurological disorders such as Parkinson’s disease and

Alzheimer’s disease.

The potential of gene therapy to treat specific human diseases, has hardly become

apparent yet but it is believed be the way forward in the treatment of many diseases.

Trials in United States are being carried out in an attempt to treat AIDS. The strategies

are in the form of a treatment which will protect susceptible cells from infection by the

virus once it is in the body, or to inhibit the replication of HIV in already affected cells.

Moreover to try to boost the immune response to HIV and HIV-infected cells. This and

many other diseases have become to show potential of being treated in this fashion.

Gene therapy has resulted in the possible reduction in cancerous tumours.

Tumours in lung cancer patients shrunk or stopped growing when scientists inserted

healthy genes into to replace defective or missing genes, it demonstrated that by

correcting a single genetic abnormality in lung cancer cells may be enough to slow down

or stop the spread of cancer. Further research into the use of gene therapy to cure or help

cancer victims has been continued after the discovery of this method.

As well as in medicine there are many applications of genetic engineering in

agriculture. Genetically engineered hormones are available, and may be used in the

future to increase meat or milk yields of livestock. Soon disease may be wiped out with

the use of genetically engineered vaccines. Fertilisers may become obsolete, as scientists

attempt to introduce ntirogenase genes into plants, the gene coding for the enzyme that

catalyses the breakdown of atmospheric nitrogen. Plants could also in theory be able to

produce their own insecticides thus making artificial ones obsolete. Crops could even be

engineered to grow in naturally inhospitable areas and could effectively make food

shortages a thing of the past.

Recently, genetic technology has shown that it will affect our everyday lives, such

as in the grocery store. There has been work in the growing of genetically engineered

foods. The government has even approved the sale of certain products. The nutritional

value can be increased, as well as the hardiness of crops.

Another interesting idea is that of transgenic animals. Transgenic technology

bypasses conventional breeding by using artificially constructed parasitic genetic

elements as vectors to multiply copies of genes, and in many cases, to carry and smuggle

genes into cells that would normally exclude them. (Parasites, by definition, require the

host cell’s biosynthetic machinery for replication.). Once inside cells, these vectors slot

themselves into the host genome. In this way, transgenic organisms are made carrying the

desired transgenes. The insertion of foreign genes into the host genome has long been

known to have many harmful and fatal effects including cancer; and this is borne out by

the low success rate of creating desired transgenic organisms. Typically, a large number

of cells, eggs or embryos have to be injected or infected with the vector to obtain a few

organisms that successfully express the transgene(s).

The most common vectors used in gene biotechnology are a mosaic

recombination of natural genetic parasites from different sources, including viruses

causing cancers and other diseases in animals and plants, with their pathogenic functions

‘crippled’, and tagged with one or more antibiotic resistance ‘marker’ genes, so that cells

transformed with the vector can be selected. For example, the vector most widely used in

plant genetic engineering is derived from a tumour-inducing plasmid carried by the

bacterium Agrobacterium tumefaciens. In animals, vectors are constructed from

retroviruses causing cancers and other diseases. Unlike natural parasitic genetic elements

that have varying degrees of host specificity, vectors used in genetic engineering are

designed to overcome species barriers, and can therefore infect a wide range of species.

Thus, a vector currently used in fish has a framework from the Moloney murine

leukaemic virus, which causes leukaemia in mice, but can infect all mammalian cells. It

has bits from the Rous Sarcoma virus, causing sarcomas in chickens, and from the

vesicular stomatitis virus, causing oral lesions in cattle, horses, pigs and humans.

Genetic fingerprinting is a well-known application of genetic engineering, it is

often used in an aid to identify the perpetrator of a crime. This is possible because

everyone (except identical twins) has a unique genetic fingerprint. The process was

developed by Alecs Jeffreys at the University of Leicester in 1984. He noticed that there

were unusual sequences in DNA that seemed out of place. These sequences

(minisatellites) are repeated many times throughout DNA. A DNA probe is used to

analyse these patterns. A DNA probe is a synthetic length of DNA made up of a repeated

sequence of bases. This is cloned to make a batch of probes using the recombinant DNA

into E. Coli bacterium technique. A radioactive label is then attached by exchanging all

the phosphate molecules with radioactive isotopes of the same species. The DNA which

is to analysed is then fragmented using a restriction enzyme, placed on agarose gel and

the fragments separated using a process called electrophoresis. Fragments of DNA have

negative charges, so when and anode is placed at the other end of the gel, the DNA is

attracted to it. The distances they move are dependent on the size of the fragment, with

the lighter, shorter fragments moving the furthest. Once they are separated, the fragments

are transferred to a nylon membrane are treated with the DNA probe. These bind to any

complementary minisatellite sites, and make them show up on x-ray film because of the

radioactivity. The pattern of bands revealed is known as the DNA fingerprint. This would

seem fail safe, but there are many problems associated with this technique. Samples

taken from the victim’s body will more than likely have the victims DNA as well, not to

mention any bacterial or fungal DNA present. Dyes used in clothes can also alter

restriction enzymes, making them fragment in the wrong place. DNA fingerprinting is

therefore not infallible.

People rightly fear that what they eat could harm them if it has been gene altered.

It is also quite possible that products can be made safer and less allergenic than before

this new technology. If food can be grown more economically as a product of gene

technology, world hunger can be virtually stamped out.

It is feared by some people that we might knock nature off balance by interfering

with it. There is no possible way that it could truthfully be said that we haven’t done so

already. Ever since we discovered how to make fire, we have defeated nature’s balance. It

does not take genetic medicine to increase our populations beyond what natural barriers

had been in place, such as disease and famine.

When the possible threats and the potentially helpful applications are weighed it

appears that research into the possibilities should continue. If people’s fears of what can

be done wrong were to stop the industry it still would not insure that in the future the

technology won’t be used in such a way. If future governments really wanted to they

could rediscover it and use it immorally, regardless of what we do now. Scientists should

learn how to use it safely and responsibly now so that, hopefully, future scientists will do

the same.

The current ethic followed by genetic scientists does not allow genetic

manipulation in human embryos. Lack of knowledge does keep scientists wary of what

they are doing in human genetics. However, their caution is somewhat less with other

animals.

Genetic engineering has and will undoubtedly provide the means to help

mankind. But we must consider whether it is socially or ethically desirable. Along with

technology must go an ethical evaluation. Early trials with growth enhanced pigs

revealed disastrous side-effects for the animals.