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DNA replicationThe formation of new and, hopefully, identical copies of complete genomes. DNA replication occurs every time a cell divides to form two daughter cells. Under the influence of enzymes, DNA unwinds and the two strands separate over short lengths to form numerous replication forks, each of which is called a replicon. The separated strands are temporarily sealed with protein to prevent re-attachment. A short RNA sequence called a primer is formed for each strand at the fork. These primers provide a free 3'-OH end on which the new complementary sequence can be formed along the strand. The LEADING STRAND is synthesized continuously in the 5’ to 3’ direction, working towards the fork direction with removal of the RNA primers as the parental duplex is unwound. The LAGGING STRAND is synthesized discontinuously in the opposite direction as short fragments called Okazaki fragments. Lagging strand synthesis requires extension of the primer, then removal of the primers and gap filling. At least 20 different enzymes and factors, including DNA helicases, DNA polymerases, RNA primases, DNA TOPOISOMERASES and DNA ligases are involved in the complex process of DNA replication.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
DNA replicationsee DNA.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005