DNA Replication

DNA replication produces two new daughter DNA strands that are identical to the original DNA. The resulting DNA strands are semi-conservative, as they contain one strand from the original DNA molecule and one newly synthesized strand. The process requires DNA helicase to unwind the DNA double helix. DNA single-stranded binding proteins (SSBPs) bind to single stranded regions of DNA and help stabilize the extended single stranded templates. DNA gyrases catalyses negative supercoils and assist the unwinding process.

Leading strand
New DNA strands are intiated by RNA primers, the synthesis of which is catalyzed by enzymes called primases. In the 5’-3’ direction a continuous strand of DNA is created, the leading strand.

Lagging strand
In the 3’-5’ direction Okazaki fragments are created leading to the formation of the lagging strand. Short segments are covalently bound together by polynucleotide ligase.

Y-replication fork


DNA replication takes place at multiple points and forms replication forks which, are Y shaped structures. The progresses in both directions forming replication bubbles. The replication origins are approximately 50 to 300 kb (kilobases) apart. After initiation, elongation of the DNA is carried out by DNA polymerase III. Polymerase I subsequently removes RNA primers.