Summarizing DNA Replication in Prokaryotes

Summary

Replication in prokaryotes starts from a sequence found on the chromosome called the origin of replication—the point at which the DNA opens up. Helicase opens up the DNA double helix, resulting in the formation of the replication fork. Single-strand binding proteins bind to the single-stranded DNA near the replication fork to keep the fork open. Primase synthesizes an RNA primer to initiate synthesis by DNA polymerase, which can add nucleotides only in the 5' to 3' direction. One strand is synthesized continuously in the direction of the replication fork; this is called the leading strand. The other strand is synthesized in a direction away from the replication fork, in short stretches of DNA known as Okazaki fragments. This strand is known as the lagging strand. Once replication is completed, the RNA primers are replaced by DNA nucleotides and the DNA is sealed with DNA ligase, which creates phosphodiester bonds between the 3'-OH of one end and the 5' phosphate of the other strand.

Glossary

helicase

during replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds

lagging strand

during replication, the strand that is replicated in short fragments and away from the replication fork

leading strand

strand that is synthesized continuously in the 5'-3' direction which is synthesized in the direction of the replication fork

ligase

enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand

primase

enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand

primer

short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides

replication fork

Y-shaped structure formed during initiation of replication

single-strand binding protein

during replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

topoisomerase

enzyme that causes underwinding or overwinding of DNA when DNA replication is taking place