DNA Polymerase (Elongation...)
DNA Polymerase → Enzyme that replicate/synthesise DNA
- Polymerase I : 928 amino acid polypeptide (MW around 103kDa)
- Adds the correctly paired nucleotides to a template strand
- Catalysed synthesis of DNA in vitro when provided with: (all 4 nucleotides, template strand and primer).
- E.coli → have many different DNA polymerase (Polymerase I-V, order of discovery).
- Incoming dNTP's (deoxy-nucleotides-tri phosphate) form H bonds with template strand according to AT/GC rule (complementarity)
- DNA polymerase breaks bonds between 1st and 2nd phosphate in dNTP releasing pyrophosphate (PPi)
- Action provides energy to form a covalent bond between dNMP (deoxy-nucleotide-mono-phosphate) and nucleotide in growing chain.
Properties of DNA polymerases
- Whether prokaryotic or eukaryotic, all share the following properties:
- Incoming base is selected within DNA polymerase active site by Watson-Crick AT-AG pairing with template strand.
- Chain growth is in the 5' to 3' direction and is anti-parallel to template strand.
- DNA polymerases can't initiate DNA synthesis de novo (starting from the beginning) - require an olgionucleotide primer with a free 3'-OH group to build upon.
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