Overview of DNA Replication

Key Concepts

• DNA Replication: Process where a single DNA molecule with two strands replicates to form two identical DNA molecules.
• Parent Strands: Original strands in the DNA molecule.
• Daughter Strands: Newly synthesized strands.
• Semi-Conservative Replication: Method where each new DNA molecule retains one parent strand and one new daughter strand.
• Replication Bubble: Region where DNA unwinds and replication begins.

Replication in Prokaryotes

Key Enzymes and Proteins

• DNA A Protein: Initiation factor; promotes unwinding of DNA at ORI site.
• DNA B Protein (Helicase): Breaks hydrogen bonds between strands to open replication fork.
• DNA C Protein: Assists DNA B by loading it onto DNA; acts as a loading factor.
• DNA G Protein (Primase): Synthesizes short RNA strands needed for DNA polymerase to start.
• DNA Gyrase (Topoisomerase II): Induces negative supercoiling to relieve stress during unwinding.
• DNA Ligase: Joins DNA segments on the lagging strand.
• DNA Polymerases:
  • DNA Polymerase I: Fills gaps after RNA primer removal.
  • DNA Polymerase II: Involved in DNA repair.
  • DNA Polymerase III: Main enzyme for DNA replication; has a beta subunit acting as a DNA clamp.
• RNase Enzyme: Removes ribonucleotides from RNA primers.
• SSB Proteins (Single-Strand Binding Proteins): Prevents strands from re-annealing.
• Tus and Ter Proteins: Terminate DNA replication by halting helicase.

Replication in Eukaryotes

Key Enzymes and Proteins

• ORC (Origin Recognition Complex): Recognizes and binds to origin of replication.
• CDC6 Protein: Part of pre-replication complex; loads MCM to ORC.
• CDT1 Protein: Ensures DNA replicates only once per cell cycle.
• MCM Protein (Mini Chromosome Maintenance): Helicase enzyme, opens replication fork.
• RPA Protein: Prevents strands from binding to themselves.
• PCNA Protein: DNA clamp that maintains DNA polymerase processivity.
• DNA Polymerases:
  • Polymerase Alpha: Primase activity, helps in initiation.
  • Polymerase Beta: DNA repair.
  • Polymerase Gamma: Mitochondrial DNA replication and repair.
  • Polymerase Delta: Main replication enzyme, synthesizes both leading and lagging strands.
  • Polymerase Epsilon: Role is ambiguous.
• DNA Topoisomerases: Help in DNA unwinding through negative supercoiling.

Conclusion

• Understanding the roles of these enzymes and proteins is crucial for comprehending DNA replication in both prokaryotic and eukaryotic organisms.