Here's a breakdown of the key elements involved in DNA replication:
1. Unwinding and Separating the Double Helix:
- The DNA molecule is unwound by an enzyme called helicase.
- This unwinding creates two separate strands, each acting as a template for the synthesis of a new strand.
2. Primer Binding:
- A short RNA sequence called a primer binds to the template strand.
- This primer provides a starting point for the DNA polymerase enzyme.
3. DNA Polymerase Activity:
- DNA polymerase is the key enzyme responsible for synthesizing new DNA strands.
- It reads the template strand and adds complementary nucleotides to the new strand, following the base pairing rules (A with T, and G with C).
- DNA polymerase can only add nucleotides to the 3' end of a growing strand.
4. Leading and Lagging Strand Synthesis:
- One strand (leading strand) is synthesized continuously in the 5' to 3' direction, following the movement of the replication fork.
- The other strand (lagging strand) is synthesized discontinuously in short fragments called Okazaki fragments.
- This is because the lagging strand is synthesized in the opposite direction of the replication fork.
5. Joining of Fragments:
- The Okazaki fragments on the lagging strand are joined together by an enzyme called DNA ligase.
6. Proofreading:
- DNA polymerase has proofreading capabilities, ensuring that the new strand is a faithful copy of the original.
- It can remove incorrect nucleotides and replace them with the correct ones.
The semi-conservative model ensures that:
- Each new DNA molecule inherits one strand from the parent molecule, preserving the genetic information.
- The process is accurate, thanks to the proofreading capabilities of DNA polymerase.
This fundamental process allows for the duplication of DNA, ensuring that each daughter cell receives a complete set of genetic instructions.
