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Enzymes Involved in DNA Replication
By- Naziya Khaliquz Subhan
B.Tech (BT)
Enzymes
• Helicase
• Topoisomerase
-> SSB (binding protein)
• RNA Polymerase
• DNA Polymerase
• RNAse H
• DNA Ligase
Helicase
• Also k/a Helix destabilizing enzyme
or Unwindase.
• Unwind the DNA helix using hydro-
lysis of ATP.
• They are motor proteins that move directionally along
the nucleic acid phosphodiester backbone.
Topoisomerase
• Relieve the winding strain generated during
unwinding of the DNA by introducing a nick
in DNA.
• Topoisomerase I - cut the ssDNA.
• Topoisomerase II – cut the dsDNA.
Single Strand Binding Protein
• Binding protein that binds to ssDNA and
prevent the double helix from re-annealing
after DNA helicase unwinds it.
• Maintains the strand separation and facilitate
the synthesis of nascent DNA.
DNA Primase
• Attaches Primer and provide a starting
point to DNA for DNA Polymerase to
begin synthesis of new DNA strand.
• It is a type of RNA Polymerase.
DNA Polymerase
• DNA Polymerase III:
- added nucleotide in 5’ to 3’ direction.
- consist of three subunit: α, Ɛ, θ
α- polymerase activity
Ɛ- exonucleolytic proofreader
θ- stabilizer for Ɛ.
DNA Polymerase
• DNA Polymerase II:
- 3’ to 5’ exonuclease activity and DNA repair.
- encoded by polB gene.
• DNA Polymerase I:
- both 3’ to 5’ & 5’ to 3’ exonuclease activity.
- processing of okazaki fragments.
- encoded by polA gene.
Ribonuclease H
• RNAse H- endonuclease.
• Removes RNA primer as it possess the
capability to cleave the RNA by hydrolytic
mechanism; allowing completion of newly
synthesized DNA.
*DNA Polymerase-I can also remove the RNA Primer.
Ligase
• Joints okazaki fragment of lagging strand by
catalyzing the formation of Phosphodiester
bond.
• Mechanism:
- Adenylation (Addition of AMP).
-Transfer of AMP to 5’ phosphate of donor.
-Formation of Phosphodiester bond between
5’ phosphate of donor and 3’ hydroxyl of acceptor.
Enzymes
Comparison
Prokaryotes-
• DNA polymerase – I
• DNA Polymerase - II
• DNA Polymerase – III
• DNA Gyrase
Eukaryotes-
• DNA Polymerase β
• DNA Polymerase δ
• DNA Polymerase α, Ɛ
• Topoisomerase
Thank you!

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Enzymes involved in dna replication

  • 1. Enzymes Involved in DNA Replication By- Naziya Khaliquz Subhan B.Tech (BT)
  • 2. Enzymes • Helicase • Topoisomerase -> SSB (binding protein) • RNA Polymerase • DNA Polymerase • RNAse H • DNA Ligase
  • 3. Helicase • Also k/a Helix destabilizing enzyme or Unwindase. • Unwind the DNA helix using hydro- lysis of ATP. • They are motor proteins that move directionally along the nucleic acid phosphodiester backbone.
  • 4. Topoisomerase • Relieve the winding strain generated during unwinding of the DNA by introducing a nick in DNA. • Topoisomerase I - cut the ssDNA. • Topoisomerase II – cut the dsDNA.
  • 5. Single Strand Binding Protein • Binding protein that binds to ssDNA and prevent the double helix from re-annealing after DNA helicase unwinds it. • Maintains the strand separation and facilitate the synthesis of nascent DNA.
  • 6. DNA Primase • Attaches Primer and provide a starting point to DNA for DNA Polymerase to begin synthesis of new DNA strand. • It is a type of RNA Polymerase.
  • 7. DNA Polymerase • DNA Polymerase III: - added nucleotide in 5’ to 3’ direction. - consist of three subunit: α, Ɛ, θ α- polymerase activity Ɛ- exonucleolytic proofreader θ- stabilizer for Ɛ.
  • 8. DNA Polymerase • DNA Polymerase II: - 3’ to 5’ exonuclease activity and DNA repair. - encoded by polB gene. • DNA Polymerase I: - both 3’ to 5’ & 5’ to 3’ exonuclease activity. - processing of okazaki fragments. - encoded by polA gene.
  • 9. Ribonuclease H • RNAse H- endonuclease. • Removes RNA primer as it possess the capability to cleave the RNA by hydrolytic mechanism; allowing completion of newly synthesized DNA. *DNA Polymerase-I can also remove the RNA Primer.
  • 10. Ligase • Joints okazaki fragment of lagging strand by catalyzing the formation of Phosphodiester bond. • Mechanism: - Adenylation (Addition of AMP). -Transfer of AMP to 5’ phosphate of donor. -Formation of Phosphodiester bond between 5’ phosphate of donor and 3’ hydroxyl of acceptor.
  • 12. Comparison Prokaryotes- • DNA polymerase – I • DNA Polymerase - II • DNA Polymerase – III • DNA Gyrase Eukaryotes- • DNA Polymerase β • DNA Polymerase δ • DNA Polymerase α, Ɛ • Topoisomerase