DNA Replication
The major event in S-phase is DNA replication. The goal of this process is to create exactly two identical semi-conserved chromosomes. The cell prevents more than one replication from occurring by loading pre-replication complexes onto the DNA at replication origins during G1-phase which are dismantled in S-phase as replication begins. In budding yeast, Cdc6 is degraded, Orc2/6 are phosphorylated and mcm proteins are excluded from the nucleus, preventing re-attachment of the replication machinery (DNA polymerase) to the DNA after initiation. Incredibly, DNA synthesis can occur as fast as 2000 nucleotides/second and must be as accurate as 2 wrong base in 1010 nucleotide additions.
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