1. Unwinding and Separation:
* The DNA double helix is unwound by an enzyme called helicase.
* This unwinding creates a replication fork, a Y-shaped structure where the two strands are separating.
* Single-strand binding proteins (SSBs) stabilize the separated strands, preventing them from re-annealing.
2. Primer Synthesis:
* An enzyme called primase creates a short RNA primer, which provides a starting point for DNA polymerase to bind to.
3. New Strand Synthesis:
* DNA polymerase binds to the primer and starts adding nucleotides to the new strand, using the existing DNA strand as a template.
* DNA polymerase can only add nucleotides in the 5' to 3' direction.
* This creates two new DNA strands, one continuous (leading strand) and one discontinuous (lagging strand).
4. Lagging Strand Synthesis:
* The lagging strand is synthesized in short fragments called Okazaki fragments.
* Each Okazaki fragment is initiated by a primer and then extended by DNA polymerase in the 5' to 3' direction.
* The gaps between the Okazaki fragments are then sealed by an enzyme called DNA ligase.
5. Proofreading and Repair:
* DNA polymerase has a proofreading ability, which helps to minimize errors in the newly synthesized strands.
* Other repair mechanisms exist to correct any remaining errors.
6. Termination:
* Replication ends when the two replication forks meet on the opposite side of the chromosome.
Key Enzymes involved in DNA Replication:
* Helicase: Unwinds the DNA double helix.
* Primase: Synthesizes RNA primers.
* DNA polymerase: Extends the new DNA strands, using the existing strand as a template.
* DNA ligase: Seals the gaps between Okazaki fragments.
Overall, DNA replication is a complex and tightly regulated process that ensures the accurate duplication of the genome before cell division, enabling the transmission of genetic information from one generation to the next.
