Restriktsiooniensüümid

Restriktsiooniensüümid, also known as restriction enzymes or restriction endonucleases, are a class of enzymes that cleave DNA molecules at specific recognition nucleotide sequences known as restriction sites. These enzymes are naturally found in bacteria and archaea, where they play a crucial role in defending against bacteriophages by degrading foreign DNA.

The discovery of restriction enzymes in the 1960s revolutionized molecular biology. Scientists found that bacteria possessed a mechanism to distinguish between their own DNA and invading viral DNA, and that this mechanism involved enzymes that cut the foreign DNA at specific points. These enzymes became invaluable tools for recombinant DNA technology.

Restriction enzymes are categorized into three main types based on their mode of action, cleavage site, and cofactor requirements. Type I enzymes cut DNA at sites different from their recognition sequence and require ATP and S-adenosylmethionine for activity. Type II enzymes recognize and cut DNA within their specific recognition sequence, and they are the most commonly used in molecular biology labs as they produce predictable fragments. Type III enzymes cleave DNA at a site adjacent to their recognition sequence and require ATP.

The ability of restriction enzymes to cut DNA at precise locations allows scientists to manipulate DNA fragments. This is fundamental for techniques such as gene cloning, DNA fingerprinting, and genetic engineering. By using different restriction enzymes, scientists can generate specific DNA fragments that can then be inserted into vectors or analyzed for genetic variations. The specific sequences recognized by these enzymes are typically short palindromic sequences.