RESTRICTION ENZYMES

=RESTRICTION ENZYMES= ''(also called restriction endonuclease) [image:http://i.imgur.com/mZhglMZ.gif] Restriction enzymes were first discovered when it was noticed that some bacteria could cut up foreign DNA, making them resistant to bacteriophage viruses. Scientists soon discovered a series of enzymes that would cut at specific DNA sequences known as restriction sites. The enzymes catalyse the breaking of the phosphodiester bonds between the sugar and phosphate groups of the of each DNA backbone. However, their shape only allows them to do this at points on the DNA with a specific sequence (usually 4-8 bases). Some restriction enzymes cut DNA leaving ‘blunt’ ends, while others cut DNA leaving ‘Sticky’ ends - a short overhang of single stranded DNA that can base-pair with another complementary 'sticky end' [image:http://i.imgur.com/XEaDcCH.png] [image:http://i.imgur.com/ZGEPOqD.png] ==Restriction Fragment Length Polymorphism (RFLP)== DNA can be cut into pieces using different restriction enzymes. Restriction enzymes only cut DNA at very specific sequences. Therefore when DNA from a particular individual its cut it always produces a specific pattern of different sized fragments. Another individual (with a slightly different sequence) might be missing one of these cut sites or have an extra one and will produce a set of different sized DNA fragments.