DNA replication is the process by which DNA is doubled, and it occurs in several steps that involve multiple proteins called replication enzymes, as well as RNA. The basic steps of DNA replication are:
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Initiation: The DNA double helix is unwound and separated into two strands. This is carried out by an enzyme called helicase, which breaks the hydrogen bonds holding the complementary bases of DNA together (A with T, C with G). The separation creates a Y shape called a replication fork, and the two single strands of DNA now act as templates for making new strands of DNA.
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Elongation: Enzymes create short RNA primers on each strand. DNA polymerase enzymes add nucleotides to the new strand in the 5 to 3 direction. Nucleotides are added continuously on the leading strand, while nucleotides are added in short fragments called Okazaki fragments on the lagging strand. DNA polymerase removes the RNA primers and replaces them with DNA nucleotides. Ligase joins the Okazaki fragments together on the lagging strand.
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Termination: The result is two identical copies of the original DNA molecule. DNA replication is a very complex process, and if any error is made during the replication, it may lead to mutation. The DNA polymerase I and polymerase III act as proofreaders of the newly synthesized DNA.
The following description of this three-stage process applies generally to all cells, but specific variations within the process may occur depending on the organism and cell type.
