Polymeraasien

Polymeraasien, or polymerases, are a broad class of enzymes that catalyze the synthesis of nucleic acids. They use a template strand to guide the addition of nucleotide units, forming phosphodiester bonds to extend a growing DNA or RNA chain. Most polymerases work in the 5' to 3' direction and require a primer to start synthesis, along with divalent metal ions such as magnesium for catalysis. Many polymerases also possess proofreading activity, which helps maintain fidelity by removing misincorporated nucleotides.

Biological roles include DNA polymerases that replicate the genome and participate in repair, RNA polymerases that transcribe DNA into RNA, and reverse transcriptases that synthesize DNA from RNA templates. In bacteria, DNA polymerase III is the main replicative enzyme, while DNA polymerase I participates in processing and repair. In eukaryotes, a set of replicative polymerases (such as polymerases alpha, delta, and epsilon) coordinates genome duplication. RNA polymerases I, II, and III carry out transcription of ribosomal RNA, messenger RNA, and small RNAs, respectively. Archaeal and viral polymerases represent additional families. Telomerase, a specialized reverse transcriptase, maintains chromosome ends.

Technological applications are widespread. PCR relies on thermostable DNA polymerases to amplify DNA. Reverse transcription PCR (RT-PCR) uses reverse transcriptase to convert RNA into DNA before amplification. Polymerases are used in DNA sequencing, cloning, mutagenesis, and many diagnostic assays. The study of polymerases informs understanding of replication fidelity, DNA repair, and the evolution of genetic information.

History notes include the discovery of DNA polymerase by Arthur Kornberg in 1956 and the development of the Klenow fragment for research use. Modern enzymes have been engineered for stability, speed, and specificity to meet laboratory needs.