DNA Replication

• DNA replication is a semiconservative process, in which there is one parent strand and one daughter strand in the replicated DNA.
• Each parent strand is a template for ordering nucleotides to make a new complimentary strand
• There are many sites of replication on a strand of DNA called "replication bubbles", with replication forks on each ends.
• The strands in the double helix are antiparallel, so one strand runs in 5' -> 3' direction, while the other runs in 3'->5' direction
• A new DNA strand can only elongate in the 5'->3' direction

The process:

1. DNA helicase unwinds the double helix
2. DNA gyrase (bacterial enzyme) relieves the tension (produced from unwinding of DNA)
3. Single-stranded binding proteins (SSBs) keeps separated strands of DNA apart
4. Primase (RNA polymerase) makes primer, which signals Polymerase III to make complementary strand
5. DNA Polymerase III then grabs nucleotides to make complementary strands of DNA
6. One of the parental strand (3'->5' into the fork), the leading strand (growing towards the fork) can form a continuous complimentary strand (only need one single primer as the fork continues to separate and the new strand continues to elongate)
7. The lagging strand (5'->3' into the fork) has to be copied away from the fork in Okazaki fragments, in order to elongate in the 5'->3' direction (it also needs a new primer for each fragment)
8. DNA Polymerase I then replaces the RNA primer with DNA
9. DNA ligase join all the gaps that are present on the daughter strands