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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 &solid; thalassemia 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-amidase is mutated and homozygote's are unable to de-animate 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 Hormones Human 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 doesnt work correctly. Human growth hormone is only active in humans therefore a hormone from another species cannot be used in its 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 hemophiliacs sufferers of Haemophilia VIII. By introducing the correct gene for Factor VIII there is a greater chance of hemophiliacs 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.
Agriculture The 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. Crops 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 plants 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 powders Enzymes are used in biological washing powders to hydrolyses the material forming stains such as protein digesting enzymes proteases, fat emulsifier's lipases and amylase's 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 extracellular ly by bacteria such as Bacillus Subtilis grown in large scale ferments.
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 60 oC. 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 3 D 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 post
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Research essay sample on Cystic Fibrosis Genetically Engineered
