1. DNA Polymerases:
* Role: The workhorses of DNA replication. They add nucleotides to the new DNA strand, using the existing strand as a template.
* Types: There are several DNA polymerases, each with specific functions. The main ones in eukaryotes are:
* DNA Polymerase α: Initiates replication and adds short RNA primers.
* DNA Polymerase δ: Elongates the leading strand (the strand synthesized continuously).
* DNA Polymerase ε: Elongates the lagging strand (the strand synthesized in fragments called Okazaki fragments).
2. Helicase:
* Role: Unwinds the DNA double helix, separating the two strands to provide access for the replication machinery.
3. Single-Stranded Binding Proteins (SSBs):
* Role: Bind to the separated DNA strands, preventing them from re-annealing (coming back together) before they are replicated.
4. Primase:
* Role: Synthesizes short RNA primers that provide a starting point for DNA polymerase to begin replication.
5. Topoisomerases:
* Role: Relieve the torsional stress that builds up ahead of the replication fork as the DNA unwinds. They cut and rejoin the DNA strands to prevent supercoiling.
6. Ligase:
* Role: Joins the Okazaki fragments on the lagging strand to create a continuous DNA molecule.
7. Replication Origin Recognition Complex (ORC):
* Role: Binds to specific DNA sequences called origins of replication, marking the starting points for DNA replication.
8. Other Key Proteins:
* PCNA (Proliferating Cell Nuclear Antigen): Acts as a sliding clamp that keeps DNA polymerase attached to the DNA template.
* RPA (Replication Protein A): A single-stranded DNA-binding protein that helps with replication initiation and stability.
In summary:
These proteins work together in a coordinated fashion to ensure accurate and efficient DNA replication during the S phase of interphase, producing two identical copies of the genome for cell division.
