polymerasernas

Polymerasernas, commonly referred to in English as polymerases, are enzymes that catalyze the formation of nucleic acid polymers. They use a nucleic acid template to guide the incorporation of complementary nucleotides and most require a primer to initiate synthesis. Polymerases play essential roles in genome replication, transcription of RNA, and various DNA repair pathways, and they are found in all kingdoms of life and in many viruses.

DNA polymerases are responsible for copying genetic information. They synthesize DNA in the 5'→3' direction and often possess proofreading activity (3'→5' exonuclease) to correct misincorporated nucleotides. In bacteria, DNA Pol III is the main replicative enzyme, with DNA Pol I involved in processing Okazaki fragments. In archaea and eukaryotes, the primary lagging- and leading-strand polymerases include Pol δ and Pol ε, with Pol α initiating synthesis. Mitochondrial genomes are replicated by Pol γ. Eukaryotic cells also rely on specialized polymerases for DNA repair (e.g., Pol β) and translesion synthesis (Pol η, ι, κ). RNA polymerases transcribe RNA from DNA templates; in eukaryotes Pol II produces mRNA, while Pol I and Pol III transcribe rRNA and tRNA, respectively. Some viruses encode RNA-dependent RNA polymerases that synthesize RNA directly from RNA templates.

Biochemical mechanism: Most polymerases use a two-metal-ion mechanism, typically Mg2+, to catalyze nucleotide addition. The active site enforces correct base pairing, and many enzymes rely on an intrinsic proofreading exonuclease to improve fidelity. Processivity is aided by sliding clamps and accessory factors in cells.

Applications and importance: Polymerases are central to molecular biology techniques such as PCR, sequencing, cloning, and DNA labeling. Thermostable polymerases (e.g., Taq) enable rapid amplification, while high-fidelity enzymes (e.g., Pfu, Q5) reduce errors. Reverse transcriptases convert RNA to cDNA for RT-PCR and RNA sequencing. Understanding polymerases informs biotechnology, medicine, and evolutionary biology.