what happens in s phase

In S phase (the synthesis phase of the cell cycle), the cell duplicates all of its DNA so that each chromosome ends up with two identical sister chromatids, but the chromosome number itself does not change.

Quick Scoop: What happens in S phase?

• The cell’s entire genome is replicated : every DNA molecule is copied, so total DNA content doubles.

• Each chromosome that used to have one chromatid now has two identical sister chromatids joined at the centromere.

• Despite DNA doubling, the chromosome number stays the same (for example, human cells remain 46 chromosomes, but each is now duplicated).

• Centrioles in animal cells also duplicate, preparing the cell for spindle formation during later mitosis.

• DNA replication starts at many origins along the chromosomes, forming replication forks and bubbles that move until the whole genome is copied.

• Histone proteins are produced and assembled into new nucleosomes so the freshly made DNA can be tightly packaged.

• Checkpoints and repair systems monitor DNA; if errors or breaks are detected, replication can pause and repair pathways (like homologous recombination) are activated to protect genome stability.

In simple terms: S phase is when the cell quietly sits down, copies its entire instruction manual page by page, and binds the new pages together so that both future daughter cells can get a complete, identical set.

TL;DR: S phase is the DNA-copying stage of interphase where DNA content doubles, chromosomes become pairs of sister chromatids, and the cell prepares genetically for division while tightly controlling errors.

Information gathered from public forums or data available on the internet and portrayed here.