1. Unwinding and Stabilizing DNA:
* Helicase: Unwinds the double helix of DNA, separating the two strands.
* Single-strand binding proteins (SSBs): Bind to the separated strands, preventing them from re-annealing and keeping them stable.
2. Initiating Replication:
* Primase: Synthesizes short RNA primers, providing a starting point for DNA polymerase.
3. Synthesizing New DNA:
* DNA polymerase: Reads the template strand and adds complementary nucleotides to the new strand. Different DNA polymerases are involved in different stages of replication:
* DNA polymerase α: Initiates replication, but has low processivity (can't add many nucleotides before detaching).
* DNA polymerase δ: Extends the primer and replicates the lagging strand.
* DNA polymerase ε: Replicates the leading strand.
* Topoisomerases: Relieve the torsional stress created by unwinding, preventing supercoiling.
4. Proofreading and Repair:
* DNA polymerase: Has a proofreading function, correcting any mismatched nucleotides during replication.
* Exonucleases: Remove mismatched nucleotides, helping to maintain DNA fidelity.
5. Ligating the Fragments:
* DNA ligase: Joins the Okazaki fragments (short segments synthesized on the lagging strand) into a continuous strand.
Summary of Enzyme Roles in DNA Replication:
* Unwinding and Stabilizing: Helicase, SSBs
* Initiating Replication: Primase
* Synthesizing New DNA: DNA polymerase α, δ, ε, Topoisomerases
* Proofreading and Repair: DNA polymerase, Exonucleases
* Joining Fragments: DNA ligase
This intricate interplay of enzymes ensures that DNA replication is a highly controlled and accurate process, vital for the transmission of genetic information from one generation to the next.
