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Restriction Map and Gel Electrophoresis
Once we produce as many copies of a gene as we would like, we then usually create the restriction map for that particular gene. A restriction map is a description of all the different sites on the gene where restriction enzymes can act. The restriction map is created with the help of a process known as gel electrophoresis. Suppose that we take a certain gene, mix it with some specific restriction enzyme and produce three unequally-sized fragments of DNA. In order to determine their physical size with respect to one another, we would have to expose them to gel electrophoresis. In gel electrophoresis, the three fragments are placed into a special gel that contains pores of some determined size. The entire apparatus is connected to a voltage source (battery), which creates an electric field between the two sides of the plate. Since DNA molecules are negatively charged due to the phosphate groups, they will naturally move from the negatively-charged end (cathode) to the positively-charged end (anode). Those DNA fragments which are smallest will end up the farthest along the plate because they are able to easily move along and through the pores of the gel. The larger fragments will not be able to move as quickly through the pores and so will end up being the closest to the beginning (cathode end). At the end of the gel electrophoresis process, we have successfully separated the DNA fragments on the basis of their physical size.
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