원핵생물에서의 복제

In prokaryotes, DNA replication begins when initiator proteins bind to the origin of replication, a small region of DNA containing a specific sequence of bases, creating a complex.

This complex helps to initially separate the DNA. Then the enzyme DNA helicase binds to it and continues to unwind the DNA by breaking the hydrogen bonds between the complementary strands. The newly opened areas are stabilized by single-stranded DNA binding proteins. Each one can now serve as a template for the synthesis of a new strand of DNA.

The unwinding and synthesis proceeds in both directions from the origin, creating two replication forks. In front of the forks, topoisomerase enzymes bind to the DNA and reduce torsional strain as the molecule unwinds.

Once the strands are separated, another enzyme, primase, synthesizes an RNA primer, a short stretch of RNA complementary to the DNA sequence. The primer provides a place for the enzyme DNA polymerase to add nucleotides complementary to the DNA sequence, creating a new DNA strand in a process called elongation.

DNA polymerase synthesizes DNA in the five prime to three prime direction of the molecule, so the synthesis of this strand, the leading strand, proceeds continuously. The other strand, the lagging strand, has the opposite orientation. Consequently DNA is synthesized in short pieces called Okazaki fragments, elongated from additional RNA primers backwards from the overall direction of movement of the replication fork.

The RNA primers are then excised by enzymes such as RNAs, replaced with DNA, and the DNA fragments are joined together by the enzyme DNA ligase, creating a continuous strand.

DNA replication proceeds around the entire molecule, resulting in two circular DNA molecules. This is considered a semiconservative process, because each molecule contains one old strand and one new strand.