cellcycle

The cell cycle is the series of events that a cell goes through to grow and divide, ensuring that genetic material is accurately replicated and partitioned into daughter cells. In eukaryotic cells, the cycle is organized into interphase, which includes G1, S, and G2, and the M phase, which comprises mitosis and cytokinesis. Some cells may enter a quiescent state known as G0 from G1.

During G1, cells increase in size and synthesize RNA and proteins necessary for DNA replication; they also assess whether conditions are favorable for division. The G1/S checkpoint commits the cell to DNA synthesis if the environment is suitable. S phase is when the genome is replicated, producing two identical sister chromatids for each chromosome. In G2, the cell continues to grow and produces components needed for mitosis; the G2/M checkpoint checks that DNA replication has been completed accurately and that the cell is ready to enter mitosis. M phase starts with mitosis, where chromosomes condense and are equally segregated into two nuclei, followed by cytokinesis, which divides the cytoplasm and completes cell division.

Progress through the cycle is driven by cyclin-dependent kinases (CDKs) bound to cyclins. The activity of CDK-cyclin complexes is tightly regulated and coordinated with checkpoints to prevent progression when DNA is damaged or not fully replicated. The tumor suppressor p53 plays a key role in responding to DNA damage by activating arrest or apoptosis if repair is not possible.

The cell cycle exhibits variation among cell types and organisms; many specialized cells can slow or halt the cycle, and dysregulation can contribute to cancer and developmental disorders. In bacteria and archaea, the cycle is simpler and typically linked to growth and binary fission rather than the eukaryotic phase structure.