Polimerases

Polymerases are enzymes that synthesize polymers, most notably nucleic acids. They catalyze the formation of phosphodiester bonds between nucleotides using a template strand to determine sequence and direction. Most DNA polymerases require a primer with a free 3' end to initiate synthesis, whereas many RNA polymerases can start chains de novo. Like other nucleic acid–metabolizing enzymes, polymerases rely on divalent metal ions, typically Mg2+ (and sometimes Mn2+), to coordinate substrate binding and catalysis.

They are broadly classified into DNA polymerases, RNA polymerases, and reverse transcriptases. DNA polymerases copy the genome and participate in DNA repair. In bacteria and archaea, replicative polymerases such as DNA polymerase III and various repair polymerases operate during genome maintenance; in eukaryotes, multiple DNA polymerases (alpha, delta, epsilon for replication; gamma for mitochondrial DNA) carry out genome duplication and repair, with specialized translesion polymerases (eta, iota, kappa) allowing replication past damaged bases. RNA polymerases synthesize RNA from a DNA or RNA template; in eukaryotes, RNA polymerase II transcribes mRNA, while bacteria have a single RNA polymerase holoenzyme with sigma factor; archaea have RNA polymerases related to the eukaryotic ones. Reverse transcriptases are RNA-dependent DNA polymerases that generate DNA from RNA templates and are central to retroviruses and many molecular biology techniques, such as RT-PCR.

Polymerases are organized into structural families (A, B, C, D, X, Y) with characteristic active sites and proofreading abilities. Many DNA polymerases possess 3' to 5' exonuclease activity that increases fidelity; some specialized polymerases lack proofreading but can bypass lesions, aiding DNA damage tolerance.

Applications include PCR using thermostable DNA polymerases (for example, Taq, Pfu, Q5), cloning, sequencing, and diagnostic assays. The study of polymerases informs fields from genetics and molecular biology to forensic science and medicine.