DNA Polymerase | Online Biotech Notes

DNA Polymerase

• The search for an enzyme that could synthesize DNA began in 1952.
• It is first purify & characterized by Arthur Kornberg from E-coli.
• There are 3 different types of DNA polymerases present in E-coli DNA. Polymerase T, DNA polymerase II & DNA Polymerase III.
• Their properties are given below in the table.

	I	II	III
Natural Gene	Pol A	Pol B	Pol C(dnae)
Subunits (no. of different types)	1	7	>=10
Mr (Relative molecular weight)	103000	88000	791500
3’-5’ Exonuclease (Proofreading)	Yes	Yes	Yes
5’-3’ Exonuclease	Yes	NO	No
Polymerization rate(nucleotides)	16-20	40	250-1000
Processiveity  (Nucleotides added before polymerases dissociates )	3-200	1500	>=500000

Note:-Polymerase III is the main polymerizing enzyme present in prokaryotes.

Mechanism of DNA Polymerase

The 3’-OH of sugar act as nucleophile & attack on alpha phosphate of incoming nucleotide, with the release of pyrophosphate (ppi) and formation of phosphodiester bond.

Function of DNA Polymerases

• The main function of DNA polymerase to form phosphodiester bond.
• This enzyme involved in DNA replication.
• This enzyme involved in DNA repair.

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