During the S stage of interphase, the most crucial event that happens to DNA is replication. This is the process where the entire DNA molecule is copied, resulting in two identical DNA molecules. Here's a breakdown of what happens:

* Unwinding: The double helix of DNA unwinds, separating the two strands.

* Primer Binding: Short RNA sequences called primers bind to the unwound strands, providing a starting point for DNA synthesis.

* Elongation: Enzymes called DNA polymerases use the existing strands as templates to synthesize new complementary strands. This process is semi-conservative, meaning each new DNA molecule consists of one original strand and one newly synthesized strand.

* Proofreading: DNA polymerases have a built-in proofreading mechanism to ensure the accuracy of replication.

* Ligating: The newly synthesized strands are joined together by an enzyme called DNA ligase, forming two complete DNA molecules.

This process is crucial because it ensures that each daughter cell receives a complete and identical copy of the genetic information contained in the DNA.