restriktioentsyymit

Restriktioentsyymit, known in English as restriction enzymes, are enzymes produced by bacteria that recognize short, specific DNA sequences and cleave the DNA at or near those sites. They function as a defense mechanism against invading viral DNA by restricting foreign genetic material while leaving the host genome protected through methylation and other modifications.

Mechanism and features: Restriction endonucleases bind to defined sequences, which are often palindromic. Depending on the enzyme, the cut can produce cohesive ends (sticky ends) or blunt ends. Recognition sequences are usually 4 to 8 base pairs long, and the specificity of these sites enables precise fragmentation of DNA into reproducible fragments suitable for analysis and manipulation.

Classification and characteristics: Restrictioentsyymit are categorized into several types. Type II enzymes are the most widely used in molecular biology because they typically cut within or near the recognition sequence and require no ATP. Type I and Type III enzymes cut DNA at sites distant from their recognition sequences and often require ATP and additional subunits. Type IV enzymes target modified DNA, such as methylated genomes. Many restriction enzymes have isoschizomers—different enzymes that recognize the same sequence but may cut differently, allowing flexibility in experimental design.

Applications: These enzymes are fundamental tools in molecular cloning, DNA mapping, and genetic analysis. They enable the construction of recombinant DNA molecules, creation of DNA libraries, and various diagnostic approaches. Their predictable cleavage patterns have driven advances in biotechnology, genomics, and biomedical research.

History: Restriction enzymes were discovered in bacteria in the 1960s and 1970s, with foundational work by Werner Arber, Hamilton Smith, and Daniel Nathans. Their discovery and subsequent development earned the Nobel Prize in Physiology or Medicine in 1978 and catalyzed the modern era of genetic engineering.