DNA replication

DNA replication is the process of copying a double-stranded DNA molecule. Both strands serve as templates for the reproduction of the opposite strand. The process is sometimes called "semi-conservative replication" because the new DNA from the original strand contains half of the original and half of the newly synthesized DNA.

DNA replication. The double helix is unwound and each strand acts as a template. Bases are matched to synthesize the new partner strands

This process occurs in all life forms with DNA.^[1] There are some differences in the control of DNA replication in prokaryotic and eukaryotic organisms.

In a cell, DNA replication begins at specific places in the genome, called origins.^[2] As the DNA unwinds and as DNA helicase rips apart the double helix structure of DNA,^[3] the synthesis of new strands forms at a replication fork.^[4] In addition to DNA polymerase,^[5] other enzymes at the fork help to start and continue the DNA synthesis.

DNA polymerase

DNA polymerases are a family of enzymes that carry out all forms of DNA replication.^[6] However, a DNA polymerase can only extend an existing DNA strand paired with a template strand; it cannot begin the synthesis of a new strand. To begin synthesis, a short fragment of DNA or RNA, called a 'primer', is created and paired with the template DNA strand.

Many enzymes are involved in the DNA replication fork.

In general, DNA polymerases are extremely accurate, making less than one mistake for every 10⁷ (10 million) nucleotides added.^[7] Even so, some DNA polymerases also have 'proofreading' ability: they can remove nucleotides from the end of a strand in order to correct mismatched bases.

DNA repair

DNA in cells is constantly being damaged.^[8] The nucleus of cells contains a number of repair mechanisms which fix almost all of this damage. "A large set of DNA repair enzymes continuously scan the DNA and repair any damaged nucleotides".^[9]