Genetic Engineering : Gene Therapy Essay, Research Paper
Gene
therapy by gene supplementation in somatic cells may help those suffering from
genetic conditions such as cystic fibrosis. Although a mutant gene occurs in
all cells of the body only those tissues particularly affected (where the gene
is switched on) by the mutant gene would be targeted for therapy, i.e. the
lungs of a cystic fibrosis sufferer, blood cells in the bone marrow in ß
thalassaemia and the muscles in Duchemme muscular dystrophy. As
cells eventually die, so do the tissues being treated by the gene therapy
therefore the treatments have to be repeated. To
carry out gene therapy DNA must be entered into the nucleus of the cells. This
can be carried out using a number of vectors. Micro-injection is the use of a
fine needle to inject DNA into the nucleus, electroporation is an electric
pulse causing temporary holes in the membrane allowing the fine DNA strands to
enter the cell. Viruses can also be used to inject DNA into the nucleus of the
cell. The virus can be genetically engineered to remove genes that allow it to
multiply and cause disease. In some
conditions there is a gene that must be removed or neutralised, this is known
as a "gain of function" disorder. Gene supplementation is proving to
be a possible solution for some "loss of function" conditions such as
Cystic Fibrosis where a gene is missing. In the case of Cystic Fibrosis an
aerosol inhaler is being developed which will allow sufferers to take in the
missing gene into the lungs by inhaling artificially formed spheres known as
liposomes. The DNA is carried within the liposome which fuses with cells
allowing the DNA they contain to enter the cell. This treatment does not
however help with the pancreatic problems. An
example of effective gene supplementation is to treat Severe Combined
Immuno-deficiency Disease (SCID). The gene coding for adenosine de-aminase is
mutated and homozygotes are unable to de-aminate adenosine. This leads to the
death of lymphocytes therefore the sufferer has no immune system. In an
experiment some of the lymphocyte precursor cells in the bone marrow were
infected with a virus carrying the missing gene. The treatment must be repeated
every month as the lymphocytes have a life span of only a month.Human
HormonesHuman
Growth Hormone is a peptide hormone like insulin, produced in the anterior
pituitary gland. If there is a change in the genetic code the hormone produced
is different and doesn’t work correctly. Human growth hormone is only active in
humans therefore a hormone from another species cannot be used in it’s place,
as in the previous treatment for diabetes when insulin was not produced. Human
Growth Hormone causes cells to grow and multiply by directly increasing the
rate at which amino acids enter cells and are built into proteins. Human Growth
Hormone deficiency results in dwarfism and the condition can only be treated if
recognised in the early teens, before the bone plates close. Treatment is by
supplementation of the hormone. In the past the hormone was removed from the
pituitary glands of dead people and was then injected into people suffering
from lack of the hormone. Nowadays? genetic engineers can produce Human Growth
Hormone in a similar way to the production of insulin, the gene is introduced
into bacteria DNA such as E. Coli and the bacteria multiply to produce a yield
of the hormone which can then be injected into sufferers to replace the missing
gene. Factor
VIII is cloned for elimination of viral infections from blood transfusions in
light of the AIDS epidemic. Factor VIII is also one of the proteins involved in
blood clotting and is deficient in a group of haemophiliacs – sufferers of
Haemophilia VIII. By introducing the correct gene for Factor VIII there is a
greater chance of haemophiliac’s blood clotting and therefore the risk of
bleeding to death is reduced as the protein to form blood clots will be
manufactured in cells. Also
see work on diabetes mellitus.AgricultureThe
manipulation of genes of crops which are ma
to both the growers and the consumers. For the consumers the food they buy has
a longer shelf life due to the addition of a gene which slows the rotting
process. Products may be engineered to have a more desirable flavour, texture,
colour and more? nutritional. Crops
can be made more resistant to insect pests and fungi through the introduction
of natural insecticides or fungicides from species with a natural resistance.
This reduces the need for chemicals. Plants may also be made more resistant to
artificial herbicides which can be sprayed over the entire crop and destroy
only the weeds rowing without the resistant gene. Crop’s resistance to the cold
and drought nay be increased and plants may be able to grow in areas previously
unsuitable. To
manipulate genes in plants the specific gene must firstly be detected and then
all the cells which have been changed must be preserved and the unchanged cells
discarded. The desired gene is given a marker – commonly a tolerance to an
antibiotic which will kill all those cells without the gene. An
example of successful genetic engineering in plants is the formation of a
tobacco plant resistant to the Tobacco Mosaic Virus (TMV) which causes the
plant’s leaves to be covered in whitish spots. The
vector used to carry the gene into the plant is a plasmid contained in
agrobacterium tumefaciens. The bacterium normally infects dicotyledonous plants
and causes Crown Gall disease. The bacteria enters through a wound in the plant
and stimulates host cells to multiply rapidly, forming large lumps called galls
(which are the equivalent of plant tumours). A callus will cover the wound and
gall. The T-DNA from the bacteria enters the plant DNA and this is where the
bacterium becomes useful to genetically engineer plants. The plasmid genes
which control infection are different from those which cause unrestricted
growth. The latter are used for their T-DNA. The
infection genes are removed and a gene is inserted which makes the plant immune
to TMV. The plasmid no longer causes Crown Gall disease and whole plants can be
grown from single transformed cells using cloning. The cells are grown into
small calluses on agar to form tiny roots and shoots, then can be moved to
greenhouses where they grow into fully grown plants, all immune to the TMV
virus. The
potential problem is that an unchanged cell may have a natural resistance to
the antibiotic and be disease carrying which will be resistant to clinically
used antibiotics. Marker genes are therefore being developed which rely on the
presence of sugars for the plant to be able to grow. The
introduced gene may cause more problems not because of the chance of it being
poisonous – it will be broken down in the gut into small natural molecules, but
because of the chance of an allergic reaction. Extensive testing must be
carried out on the donor of the gene in case it has allergenic properties.Biological
washing powdersEnzymes
are used in biological washing powders to hydrolyse the material forming stains
such as protein digesting enzymes – proteases, fat emulsifiers – lipases and
amylases to remove starch residues. However, many enzymes denature at high
temperature and washing machines need to be hot to keep a high rate of
reaction. Most of the enzymes used are produced extracellularly by bacteria
such as Bacillus Subtilis grown in large scale fermenters. The bacteria have
been genetically engineered to produce enzymes which are stable at a high pH in
the presence of phosphates and other detergents as well as remaining active at
temps of 60oC. This is by inserting DNA from thermophilic bacteria, which to
survive in the hot springs must produce proteins which do not denature in hot
temps, so have many di-sulphide bridges holding their 3D structure in place.
Substilisin, a protease, has also had an amino acid residue replaced with an
alternative to make the enzyme more resistant to oxidation. The temperature and
presence of enzyme increase the rate of stain removal and results in a shorter
wash time and a smaller amount of washing powd