steps of DNA replication

1. Initiation

Helicase unwinds DNA at the origin of replication, creating a replication fork.

• Single-strand binding proteins (SSBs) stabilize the unwound DNA strands to prevent

reannealing.

• Topoisomerase (gyrase) relieves tension ahead of the replication fork by preventing

supercoiling.

2. Primer Binding

Primase (an RNA polymerase) adds a short RNA primer to provide a starting point for DNA polymerase

3. Elongation

DNA Polymerase III adds complementary nucleotides (dNTPs) to the 3' end of the

growing strand in the 5' to 3' direction.

• The leading strand is synthesized continuously toward the replication fork.

• The lagging strand is synthesized discontinuously in Okazaki fragments, each needing

a new primer.

4. Primer Removal and Gap Filling

DNA Polymerase I removes RNA primers and replaces them with DNA nucleotides.

5. Ligation

DNA Ligase seals gaps between Okazaki fragments by forming phosphodiester bonds,

creating a continuous strand.

6. Termination

Replication stops when the entire DNA molecule has been copied or when replication

forks meet.

• Telomerase extends the ends of linear chromosomes in eukaryotic cells to prevent loss of

genetic material