Eukaryotic Chromosome Structure

A General Model for DNA Replication

1. The DNA molecule is unwound and prepared for synthesis by the action of DNA gyrase, DNA helicase and the single-stranded DNA binding proteins.
2. A free 3'OH group is required for replication, but when the two chains separate no group of that nature exists. RNA primers are synthesized, and the free 3'OH of the primer is used to begin replication.
3. The replication fork moves in one direction, but DNA replication only goes in the 5' to 3' direction. This paradox is resolved by the use of Okazaki fragments. These are short, discontinuous replication products that are produced off the lagging strand. This is in comparison to the continuous strand that is made off the leading strand.
4. The final product does not have RNA stretches in it. These are removed by the 5' to 3' exonuclease action of Polymerase I.
5. The final product does not have any gaps in the DNA that result from the removal of the RNA primer. These are filled in by the action of DNA Polymerase I.
6. DNA polymerase does not have the ability to form the final bond. This is done by the enzyme DNA ligase.