S phase
DNA is replicated
The S phase, also known as the synthesis phase, is a phase in the cell cycle during which DNA replication takes place. During this phase, the cell makes a copy of its DNA, in order to prepare for cell division. The S phase is the stage that directly follows the G1 phase (gap 1 phase), which is a preparatory phase for DNA replication and cell growth.
In the S phase, the DNA helix unwinds and separates, and new nucleotides are added to each of the two strands of the DNA molecule. The newly synthesized DNA molecules are identical to the parent DNA, with the exception of a few errors that may occur. These errors are usually corrected by DNA repair mechanisms, which are active during the S phase.
The S phase is a critical phase of the cell cycle, as errors in DNA replication can lead to mutations in the genetic code. These mutations can affect protein synthesis and can ultimately lead to the development of diseases, including cancer. Therefore, the S phase is tightly regulated by the cell cycle checkpoints, ensuring that DNA replication proceeds only if the cell is in optimal condition and has sufficient resources to support the division.
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