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10.2.7. Enzymes involved in replication

Enzymes involved in DNA replication

Although the enzymes most involved in DNA replication are DNA polymerases, which catalyze the formation of phosphodiester bonds  between deoxyribonucleotides, adding the nucleotide complementary to that of the template chain. They need a DNA chain that serves as a template to which they will add the corresponding nucleotides, always leaving the free 3'- OH group to which more deoxyribonucleotides will be added.

The DNA polymerases of prokaryotes are different from those of eukaryotes:

The DNA polymerases from prokaryotes are :

  • DNA polymerase I
    • Remove the primer RNA.
    • Repair errors in DNA synthesis.
    • Fill the gap occupied by ribonucleotides in the primer RNA with deoxyribonucleotides.
  • DNA polymerase II
    • Repair small breaks in DNA strands (correcting these errors).
  • DNA polymerase III
    • Add the appropriate deoxyribonucleotide, complementary to that of the chain that serves as a template, in the 5'→ 3' direction.

The DNA polymerases of eukaryotes are:

  • DNA polymerase alpha and DNA polymerase delta:
    • They directly control replication.
  • DNA polymerase beta
    • Its function is to correct errors.
  • Gamma DNA polymerase
    • It controls the replication of plastid and mitochondrial DNA.

Other important enzymes in DNA replication are:

  • Primases (RNA polymerases): They synthesize the nucleotides of the primer RNA using a DNA strand as a template.
  • Gyrases (topoisomerases)Uncoil DNA chains.
  • Helicasas: They separate the two DNA strands so that they can serve as a template for the synthesis of the new ones.
  • SSB (single strand-binding) or stabilizing proteins: They keep the chains separated (which the helicase has separated) during replication so that they do not rejoin.
  • Nucleases: They break the phosphodiester bonds between nucleotides, giving rise to a "point of origin" or initiation of replication.
  • Ligaases: They join adjacent fragments through phosphodiester bonds.