ion enzymes act as a defense against invading viruses. When the viral DNA is release into the cell, the restriction enzymes cut it into pieces, rendering it useless and unable to act upon the cell. Any other bacteria entering the cell will also be cut if it contains the base sequence recognized by the enzyme. Every species of bacteria has at least one restriction enzyme. Restriction enzymes are used in genetic engineering to make complementary cuts that allow the insertion of a genetic code into a genome. In electrophoresis, restriction enzymes cut at the restriction sites on the DNA sample. It cuts as many times as the base sequence appears on the sample. After the sample is cut, buffers, dye, and a substance called ethidium bromide is added to the sample. It is then placed into the well of an agarose gel. An electrical current is run through this, and because DNA has a negative charge it is dragged through it towards the positive end. The DNA weaves through the agarose gel, the smallest pairs going the farthest simply because they are more maneuverable. The longer segments move more slowly through the agarose. When the sample has run about of the way through the gel, the current is disconnected, stopping the movement of the DNA. The gel is then placed on an ultraviolet transilluminator. Ethidium bromide is sensitive to UV rays, so it is seen under the transilluminator. A picture is then taken and the distance and base pairs can be measured and calculated.The buffer used in this is TEA buffer. It is made of Tris and EDTA. Tris keeps the pH constant at about 8.0, and EDTA pulls out low levels of sodium acetate.Since electrophoresis essentially measures the distance between restriction sites of a certain restriction enzyme, it is helpful in murder and rape cases, where blood or semen of the suspect is found as evidence. In the case of rape, a restriction enzyme is added with the blood or semen evidence. A blood sample...
