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GENETIC ENGEERING GENETIC ENGEERING Genetic engineering, also known as recombinant DNA technology, means altering the genes in a living organism to produce a Genetically Modified Organism (GMO) with a new genotype. Various kinds of genetic modification are possible: inserting a foreign gene from one species into another, forming a transgenic organism; altering an existing gene so that its product is changed; or changing gene expression so that it is translated more often or not at all. TECHNIGUES OF GENETIC ENGEERING Genetic engineering is a very young discipline, and is only possible due to the development of techniques from the 1960s onwards. These techniques have been made possible from our greater understanding of DNA and how it functions following the discovery of its structure by Watson and Crick in 1953. Although the final goal of genetic engineering is usually the expression of a gene in a host, in fact most of the techniques and time in genetic engineering are spent isolating a gene and then cloning it. This table lists the techniques that we'll look at in detail. TECHNIQUE PURPOSE Restriction Enzymes To cut DNA at specific points, making small fragments DNA Ligase To join DNA fragments together Vectors To carry DNA into cells and ensure replication Plasmids Common kind of vector Genetic Markers To identify cells that have been transformed PCR To amplify very small samples of DNA cDNA To make a DNA copy of mRNA DNA probes To identify and label a piece of DNA containing a certain sequence Gene Synthesis To make a gene from scratch Electrophoresis To separate fragments of DNA DNA Sequencing To read the base sequence of a length of DNA RESTRICTION ENZYMES These are enzymes that cut DNA at specific sites. They are properly called restriction endonucleases because they cut the bonds in the middle of the polynucleotide chain. Most restriction enzymes make a staggered cut in the two strands, forming sticky ends. ...read more.


strand is transcribed. The antisense mRNA produced will anneal to the normal sense mRNA forming double-stranded RNA. Ribosomes can't bind to this, so the mRNA is not translated, and the gene is effectively "switched off". Electrophoresis This is a form of chromatography used to separate different pieces of DNA on the basis of their length. It might typically be used to separate restriction fragments. The DNA samples are placed into wells at one end of a thin slab of gel (usually made of agarose) and covered in a buffer solution. An electric current is passed through the gel. Each nucleotide in a molecule of DNA contains a negatively-charged phosphate group, so DNA is attracted to the anode (the positive electrode). The molecules have to diffuse through the gel, and smaller lengths of DNA move faster than larger lengths, which are retarded by the gel. So the smaller the length of the DNA molecule, the further down the gel it will move in a given time. At the end of the run the current is turned off. Unfortunately the DNA on the gel cannot be seen, so it must be visualised. There are three common methods for doing this: * The gel can be stained with a chemical that specifically stains DNA, such as ethidium bromide. The DNA shows up as blue bands. * The DNA samples at the beginning can be radiolabelled with a radioactive isotope such as 32P. Photographic film is placed on top of the finished gel in the dark, and the DNA shows up as dark bands on the film. This method is extremely sensitive. * The DNA fragments at the beginning can be labelled with a fluorescent molecule. The DNA fragments show up as coloured lights when the finished gel is illuminated with invisible ultraviolet light. DNA SEQUENCING This means reading the base sequence of a length of DNA. Once this is known the amino acid sequence of the protein that the DNA codes for can also be determined, using the genetic code table. ...read more.


The Future of Gene Therapy Gene therapy is in its infancy, and is still very much an area of research rather than application. No one has yet been cured by gene therapy, but the potential remains enticing. Gene therapy need not even be limited to treating genetic diseases, but could also help in treating infections and environmental diseases: * White blood cells have be genetically modified to produce tumour necrosis factor (TNF), a protein that kills cancer cells, making these cells more effecting against tumours. * Genes could be targeted directly at cancer cells, causing them to die, or to revert to normal cell division. * White blood cells could be given antisense genes for HIV proteins, so that if the virus infected these cells it couldn't reproduce. It is important to appreciate the different between somatic cell therapy and germ-line therapy. * Somatic cell therapy means genetically altering specific body (or somatic) cells, such as bone marrow cells, pancreas cells, or whatever, in order to treat the disease. This therapy may treat or cure the disease, but any genetic changes will not be passed on their offspring. * Germ-line therapy means genetically altering those cells (sperm cells, sperm precursor cell, ova, ova precursor cells, zygotes or early embryos) that will pass their genes down the "germ-line" to future generations. Alterations to any of these cells will affect every cell in the resulting human, and in all his or her descendants. Germ-line therapy would be highly effective, but is also potentially dangerous (since the long-term effects of genetic alterations are not known), unethical (since it could easily lead to eugenics) and immoral (since it could involve altering and destroying human embryos). It is currently illegal in the UK and most other countries, and current research is focussing on somatic cell therapy only. All gene therapy trials in the UK must be approved by the Gene Therapy Advisory Committee (GTAC), a government body that reviews the medical and ethical grounds for a trial. Germ-line modification is allowed with animals, and indeed is the basis for producing GMOs. Biology notes mod 2 Genetic Engineering ...read more.

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