3 Δεκ 2012 (πριν από 4 χρόνια και 6 μήνες)

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Biotechnology, the use of living organisms to manufacture pharmaceuticals and
other products and to promote industrial processes. Microbes, such as bacteria,
and fungi were first harnessed in this way, followed by plants and most recently b
animals. “Old” biotechnology includes well
established microbial processes such as
brewing, sewage disposal, and the production of antibiotics. However, the term has
become particularly familiar since the development of genetic engineering during
the 197
0s. Much “new” biotechnology uses organisms genetically altered to work
more effectively than before, or to function in entirely new ways.

The oldest examples of what we now call biotechnology are the manufacture of
beer, wine, and other alcoholic beverage
s. Many societies in the distant past
discovered that sugary and starchy materials sometimes changed spontaneously,
generating alcohol. The phenomenon was gradually brought under conscious
control and in the 19th century the French chemist Louis Pasteur sh
owed that
fermentation was promoted by microbes. He also found that other micro
organisms, different in appearance, were responsible for processes such as vinegar

Pasteur's work not only revolutionized the technology of beer

and wine

, for example, excluding microbes that could contaminate the fermentation and
cause deleterious changes

it also indicated that other chemicals could be
manufactured in bulk by microbes. One of these was Propanone (acetone), a
solvent used to make the explo
sive cordite. During World War I the chemist Chaim
Weizmann showed that propanone could be produced by the bacterium

Today, many other chemicals are made by fermentation (a term technically
restricted to processes that occur in
the absence of air, such as alcohol production
by yeast, though it is often used more broadly). Products include oxalic acid, used
in printing and dyeing, propenoic acid (acrylic acid) used as an intermediate in the
production of plastics, lactic acid for
acidifying foods, and antifreeze. Microbes also
make many different enzymes, which are catalysts that promote chemical changes
under much milder conditions than would otherwise be required. Their applications
range from the removal of stains (by enzymes, i
ncorporated in detergents, that
attack fats and proteins) to the conversion of cornflour to high
fructose syrup, used
to sweeten soft drinks, biscuits, and cakes. Plant and animal cells can also be
cultivated in vast quantities, like microbes, to produce u
seful substances.

Another major episode in the emergence of biotechnology was the production of
penicillin from the mould

initially on a very small scale, by Howard
Florey and colleagues in Oxford during World War II. The process was soon sca
up, and other microbes were harnessed to manufacture a wide range of antibiotics
(such as streptomycin for the treatment of tuberculosis). Today, biotechnology is
facing a major challenge in developing new antibiotics to supplant those to which
causing bacteria have become resistant. One current development is the
genetic engineering of micro
organisms to synthesize “hybrid antibiotics”, whose
molecules differ from those produced naturally.

Biotechnologists now “program” bacteria to make many ot
her types of drugs that
the organisms could not otherwise produce. Human insulin, for the treatment of
diabetes, is manufactured by bacteria into which genetic engineers have introduced
the gene coding for that particular hormone. Unlike the types of insul
in obtained
from pigs and cows, it is identical with insulin secreted by the human pancreas.
Human growth hormone (used to treat children who would otherwise reach
abnormally short stature) is also made by bacteria carrying the relevant human
gene. It is f
ree of the risk of contamination with microbes such as the prion that
causes Creutzfeldt
Jakob disease, which was a danger when the hormone was
obtained from human corpses. Other pharmaceuticals manufactured by genetically
engineered micro
organisms includ
e interferons for the treatment of hepatitis B
and certain cancers, and erythropoietin, which is given to kidney
machine patients
to help them replenish the red blood cells that they lose during dialysis.

Biotechnology is beginning to revolutionize vaccine

production. Formerly limited to
weakened or killed versions of the microbes that cause disease (such as the two
alternative types of polio vaccine), researchers can now turn totally harmless
microbes into vaccines. This means introducing genes, taken from

organisms, that determine the production of particular antigens, which in
turn, induce the recipient to make protective antibodies. The technique facilitates
immunization against diseases for which fully satisfactory vaccines have no
existed hitherto. It also opens up the possibility of engineering vaccines conferring
protection against several infections simultaneously. A genetically engineered
vaccine is already widely used against the liver infection hepatitis B. Another is
g to reduce the incidence of rabies in foxes in Europe.

A rapidly developing area of biotechnology is “bioremediation”, the use of microbes
to break down pollutants in the environment, particularly the soil. One approach is
based on the fact that contamina
ted land (such as the derelict site of a former gas
works) often contains micro
organisms capable of attacking chemicals that would
be toxic to many other types of living cell. Their growth can sometimes be
massively increased by introducing nutrients or a
ir into the soil. The population of
scavengers then breaks down the pollutants. Another technique is to introduce
microbes specifically chosen for their detoxifying capacity. A third approach is to
remove the contaminated soil, expose it to scavenging micr
obes under controlled
conditions, and return it to the site afterwards.

Bacteria are used in many countries to leach metals such as iron, zinc, and
uranium out of inaccessible and low
grade ores. A tenth of the copper produced
annually in the United States

is recovered in this way. “Microbial mining” is
increasing in importance as high
grade and easily accessible mineral deposits are

Plant biotechnology has the same goal as traditional plant breeding: to develop
crops and other plants with advanta
ges such as resistance to pests and drought,
and improved palatability and nutrient content. However, more precise and
predictable results can now be achieved by modern techniques that allow individual
genes to be transferred, in contrast to the large numb
ers of genes introduced when
one plant is crossed with another by conventional methods.

A typical recent development was the development of maize that was resistant to
the European corn borer

a pest that destroys 7 per cent of the world's annual
maize crop
. The inbuilt resistance was achieved by incorporating into the plant a
gene normally carried by the soil bacterium
Bacillus thuringiensis,

which “instructs”
the maize to produce a chemical toxic to many pests. Hitherto, farmers have
controlled the corn bo
rer by spraying plants with either the bacterium or synthetic
chemicals. However, this has been an imperfect solution because there are only a
few days in the corn borer's life when spraying is effective.

Biotechnology has also yielded plants resistant to
certain viruses, fungi, and
roundworms, as well as varieties insensitive to the herbicides that farmers use to
control weeds. Quality characteristics can be improved too

for example, by
increasing the levels of certain proteins that determine the suitabili
ty of wheats for
making bread. Most recently, oilseed rape has been altered genetically to produce
chemicals of potential industrial importance. Other plants could be used in the
future to make vaccines more cheaply than by growing cultures of microbes.

Genetically Altered Plants

Ease of production is the motive behind the current emergence of biotechnology
using animals. Just as microbes and plants can be altered genetically, so new
genes may be introduced into fertilized embry
os. Thus the human gene for alpha
antitrypsin, which is used to treat the chronic lung condition emphysema, has been
incorporated into the DNA of sheep in such a way that it programmes the animals
to produce the alpha
1 antitrypsin in their milk. The sam
e method has been
adopted to direct sheep to produce blood
clotting factor IX, which is required by
people suffering from haemophilia. Other new genes have been introduced to boost
disease resistance in sheep and pigs, and to improve sheep's wool and incre
ase its
rate of growth.

Animal biotechnology has attracted criticism from animal welfare groups, which
point out that some experiments have had adverse effects on the animals.
However, scientists defending this type of work say that it is essential, from b
ethical and safety standpoints, that the animals enjoy good health (indeed better
health than most animals in the wild) and have a normal lifespan.

Correcting Genetic Diseases

Lobby groups in certain countries (especially in Germany) have opposed ot
aspects of biotechnology. One concern is the alleged unpredictability of releasing
genetically altered organisms into the environment and the possibility that the new
genes they carry may cause harm if they subsequently get into other living

It can be argued, however, that the far greater precision of genetic
engineering, as compared with gene transfers in nature, reduces rather than
increases such dangers. In addition, the official committees that regulate
biotechnology in most countries ass
ess these risks very carefully before giving
permission for particular experiments to proceed.

Other anxieties centre on the impact of modern biotechnology in poorer countries.
While its supporters emphasize benefits such as improved crop varieties and mor
effective vaccines, its opponents point to potentially adverse economic effects. In
addition to consequences for peasant farmers, who could become heavily reliant on
particular crop varieties supplied by multinational companies, there could be
adverse ma
croeconomic repercussions. For example, the transfer into bacteria of a
gene responsible for a highly desirable trait of an important cash crop (such as the
taste of vanilla) might lead to that product being made cheaply in developed
countries, with seriou
s effects on existing producers.