The synthesis (S) phase is primarily responsible for what cellular activity?

The synthesis (S) phase of the cell cycle is primarily characterized by DNA replication. During this phase, the cell duplicates its genetic material to ensure that each daughter cell receives an identical set of chromosomes during cell division. This process is crucial for maintaining genetic continuity and is a key preparation for the subsequent phases of the cell cycle, particularly mitosis, where the cell divides.

In the S phase, specific enzymes and proteins are activated to initiate and facilitate the unwinding of the DNA helix, allowing for the synthesis of new complementary strands of DNA. This ensures that when the cell divides, each new cell has a complete set of DNA to function properly.

While other cellular activities such as protein synthesis (production of enzymes) and RNA synthesis do occur in different phases of the cell cycle, they are not the primary focus of the S phase. Thus, the key task of DNA replication distinctly identifies this phase in the cell cycle.