Restriktsioonienüüm

Restriktsioonienüüm, also known as restriction enzymes, are proteins that bind to specific DNA sequences and cut the DNA at or near those sequences. These enzymes are naturally found in bacteria and archaea, where they serve as a defense mechanism against invading viruses. By cleaving the viral DNA, restriction enzymes prevent the virus from replicating and harming the host cell.

The specificity of restriction enzymes is remarkable. Each enzyme recognizes a particular DNA sequence, often called a restriction site, which is typically four to eight base pairs long. Many restriction sites are palindromic, meaning they read the same forwards and backward on opposite strands of the DNA. Once the enzyme binds to its recognition site, it cleaves the DNA backbone, creating fragments. The cut can result in either blunt ends, where both strands are cut at the same position, or sticky ends, where the cut leaves short, single-stranded overhangs.

The discovery and characterization of restriction enzymes in the 1970s revolutionized molecular biology. They became indispensable tools in genetic engineering and recombinant DNA technology. Scientists use restriction enzymes to cut DNA in a controlled manner, allowing them to isolate specific genes, construct recombinant DNA molecules, and analyze DNA fragments through techniques like gel electrophoresis. The ability to precisely manipulate DNA has been crucial for advancements in gene cloning, DNA sequencing, gene therapy, and the development of genetically modified organisms. Different types of restriction enzymes exist, classified into types I, II, III, and IV, based on their structure, mechanism of action, and the cofactors required for their activity.