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 mass produced can have many benefits

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