DNA replication is the process where the double helix containing the DNA unwinds, separates and replicates in order to form two individual copies of the the original double helix. Each new copy contains one parent strand and one daughter stand through the method of semi-conservative replication. Due to the fact that is only one old strand and one new strand, DNA must replicate in the form of a bubble. Replication fork (the edge of the bubble where the two sides meet) is the area where the DNA strand has not unwound itself protecting the sequence from being attacked by enzymes.
The following is an explanation on the process of DNA Replication:
1. DNA Helicase unwinds and unzips the double helix containing the DNA into single strands for replication through breaking apart the hydrogen bonds between the nucleotides. Simultaneously, DNA Gyrase helps to relieve the tension in the DNA while it unwind by relaxing it (Cutting both DNA strands then gluing them back together).
2. Single stranded DNA is very unstable. If left unraveled for too long, the DNA could degenerate. As the DNA strands are separated they continuously want to reconnect back into their original positions. Single-stranded binding proteins (SSBs) help to keep the two single stranded DNA separated. This is also why once the DNA unzips, it immediately starts to replicate.
3. As the 2 strands are separated they each undergo different methods of achieving a replicated DNA stand in relation to a replication fork:
- The Leading strand grows 5' to 3' into the replication fork.
- The Lagging strand grow 5' to 3' away from the replication fork, thus allowing it to only replicate in short segments called Okazaki Fragments.
4. RNA Primase attaches itself to the DNA once it has unzipped and creates a primer
5. Thereafter, DNA polymerase 3 attaches itself to the primer and begins to add the appropriate Deoxyribonucleoside Triphosphates to the 3' end of the new strand using the template strand as a guide. On the lagging strand, DNA must replicate in short segments because it cannot wait for the whole DNA to unzip then replicate as the DNA will degrade. Okazaki Fragments are created by adding Primase every so often to lagging strand. The Polymerase 3 will then add a few nucleosides. This process will continue until it reaches the replication fork
6. DNA polymerase 1 removes the primer once the polymerase 3 has replicated a section. It replaces the primer areas with the correct DNA sequences. In addition, Polymerase 1 checks for mistakes in the replicated strand and replaces them with the correct sequences.
7. Finally DNA Ligase glues the gaps between the Okazaki segments with a Phosphodiester bond.
List of Enzymes
Helicase
DNA Ligase
Primase
Gyrase
DNA Polymerase 1
DNA Polymerase 3
good job. dramatic background O_o!
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