What happens during the synthesis phase (S phase) of the cell cycle?

During the synthesis phase, also known as the S phase, the primary event taking place is DNA replication. This phase is crucial for ensuring that when a cell eventually divides, each new daughter cell will receive an identical set of chromosomes. During this process, the DNA helix unwinds, and each strand serves as a template for synthesizing a new complementary strand. The result is that each chromosome is duplicated, resulting in two sister chromatids for each original chromosome, which are held together at a region called the centromere.

Understanding this phase is essential because it sets the stage for the subsequent phases of the cell cycle. Without the accurate and complete replication of DNA during the S phase, the resulting cells may end up with missing or extra genetic information, which can lead to issues in growth, function, and even disease.