DNA Replication

*DNA replication is called semiconservative replication since there is one old strand and one new strand in the daughter DNA;DNA replicates in the form of a bubble
*the point where the DNA strands begin to be split apart is called the replcation fork
*DNA grows 5' to 3'

1.  DNA helicase unwinds and unzips the double stranded DNA into single strands for replication by breaking the hydrogen bond between the nucleotides.
2.  DNA gyrase helps to relieve the tension in the DNA as it is unwinding, by cutting both DNA strands then gluing them back together.
3.  Since single stranded DNA is very unstable, single-stranded binding proteins (SSBs) help to keep the two single stranded DNA seperated. Once the DNA unzips, it immediately starts to replicate.
4.  The 2 strands are seperated into two types of strands :
      - Leading strand--> the strand which grows 5' to 3' into the replication fork.
    - Lagging strand--> the strand that grow 5' to 3' away from the replication   fork, thus can only replicate in short segments called Okazaki Fragments.

5.  RNA Primase attaches itself to the DNA once it has unzipped and creates a primer (approx. 10-60 RNA segments that are complimentary to the parent DNA strand).
6.  With the primer on, DNA polymerase III attaches itself to the primer and begins to add nucleotides to the parent DNA strand.
7.  However on the lagging strand, the DNA must grow in short segements (Okazaki fragments) because it cannot wait for the whole DNA to unzip first then replicate, or else the DNA will degrade.
8.  DNA polymerase I removes the primers once the polymerase III has finished replicating a section. it replaces the primers with the correct DNA sequences. polymerase I also checks for mistakes in the replication and replaces it with the correct sequences.
9.  Finally DNA ligase glues the gaps between the okazaki segments with a phosphodiester bond.

a link that shows the process of DNA replication: http://www.youtube.com/watch?v=Yl754_TtJ_M