F4 DNA replication in eukaryotes

In eukaryotes, the cell cycle consists of Glr S, G2 and M phases. Most differences in the cycle times of different cells are due to differences in the length of the G, phase. Quiescent cells are said to be in the G0 phase. 

DNA replication occurs only in the S phase. It occurs at many chromosomal origins, is bi-directional and semi-conservative. Sets of 20-80 replicons act as replication units that are activated in sequence. 

DNA polymerases a and 8 replicate chromosomal DNA, DNA polymerases (3 and e repair DNA, and DNA polymerase y replicates mitochondrial DNA. 

DNA polymerase a synthesizes the lagging strand, via Okazaki fragments, and DNA polymerase 8 synthesizes the leading strand. The RNA primers are synthesized by DNA polymerase a which carries a primase subunit. 

Telomerase, a DNA polymerase that contains an integral RNA that acts as its own primer, is used to replicate DNA at the ends of chromosomes (telomeres). 

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