What does the S Phase of the cell cycle primarily involve?

During the S Phase of the cell cycle, which stands for Synthesis Phase, the primary activity is the replication of DNA. This is a crucial step because it ensures that when a cell divides, each daughter cell receives an identical set of chromosomes. The DNA molecules are duplicated, resulting in two sister chromatids for each chromosome, which are held together at the centromere. This duplication is essential for the successful completion of mitosis or meiosis, as it ensures genetic continuity from parent to daughter cells.

The importance of this phase cannot be overstated, as any errors in DNA replication can lead to mutations or cell cycle dysregulation, potentially contributing to diseases such as cancer. Thus, the S Phase sets the foundation for the later phases of the cell cycle, ensuring that genetic material is accurately passed on during cell division.