DNA Replication
- Occurs in the nucleus during the S phase of the cell cycle.
- It is an autocatalytic function of DNA.
- It occurs in a semi-conservative manner.
ORI | Sequence of base pairs in the genome where DNA replication begins. A Nick is created. |
Helicase | Helps in unwinding the two strands by breaking hydrogen bonds. |
Topoisomerase | Helps in relieving tension caused due to unwinding. |
Single stranded binding proteins | Prevents reannealing of the two strands. |
Replication fork | Y-shaped fork formed due to the separation of the two strands. |
Primase | forms the RNA primer at the ORI. |
RNA primer | Short strand of RNA formed at ORI as DNA polymerase III requires a free OH group at 3′ end to add nucleotides. |
Deoxy-Ribonucleotide | The nucleotides are high energy compounds present in triphosphate form, they act as the substrate for the new strand and also provide energy to form hydrogen bonds between nitrogenous bases. |
Polymerization | Addition of nucleotides and it always occurs in 5′→3′ direction. |
DNA polymerase III | Needed to form the new strand. Shows polymerization in 5′→3′ direction and exonuclease activity in 3′→5′ direction. |
Leading and Lagging strands | 3′→5′ strand is the leading strand as the new strand starts forming as the two strands separate. 5′→3′ strand is lagging strands as the new strand starts forming only after a short part of DNA has opened up. |
Continuous and Discontinuous | The new strand is formed in a continuous manner in the leading strand and in a discontinuous manner in the lagging strand. |
Okazaki fragments | Short fragments formed on the lagging strand. |
DNA polymerase I | Shows exonuclease and polymerization activity. Removes RNA primer and adds deoxyribonucleotides in its place. |
DNA ligase | Helps in joining of Okazaki fragments. |
