DNA Replication Process

DNA Structure

• DNA: Double-helix molecule with 2 strands
• Each strand: Sequence of 4 chemical bases (A, C, G, T)
• Complementary strands: T pairs with A, C pairs with G
• Each strand: Has a 5' end and a 3' end, running in opposite directions

Steps in DNA Replication

1. Initiation

• Helicase: Enzyme that unwinds and separates the two DNA strands, creating a replication fork
• Each separated strand acts as a template for a new strand

2. Primer Binding

• Primase: Enzyme that creates a short RNA segment called a primer
• Primer marks the starting point for replication

3. Elongation

• DNA Polymerase: Binds to the primer and adds new DNA bases in the 5' to 3' direction
• Leading Strand:
  • Made continuously in the 5' to 3' direction
• Lagging Strand:
  • Made discontinuously
  • Created in small segments called Okazaki fragments
  • Each fragment starts with an RNA primer
  • DNA Polymerase adds DNA bases to each fragment

4. Primer Removal and Gap Filling

• Exonuclease: Removes all RNA primers from both strands
• Another DNA Polymerase: Fills in gaps left by RNA primers with DNA

5. Finalization

• DNA Ligase: Seals Okazaki fragments and newly synthesized DNA to form continuous strands

Semi-Conservative Replication

• Each new DNA molecule: Composed of one old (conserved) strand and one new strand