Cell cycle
The cell cycle is the ordered sequence of growth, DNA replication, preparation, and division that lets cells produce new cells while controlling timing and genetic accuracy.
What the cell cycle is
The cell cycle is the ordered series of events a cell follows as it grows and divides. In many eukaryotic cells, it includes phases for growth, DNA replication, preparation for division, nuclear division, and cytoplasmic division. The cycle is not just a timer; it is a regulated system with checks and signals.
G1 phase
G1 is a growth and decision phase after cell division. The cell increases in size, makes proteins and RNA, senses nutrients and signals, and decides whether conditions support another round of division. Some cells can leave the active cycle and enter a nondividing state often called G0.
S phase
S phase is the DNA synthesis phase. The cell copies its genome so each chromosome becomes two sister chromatids joined at a centromere. Accurate DNA replication is essential because errors made here can be passed to daughter cells.
G2 phase
G2 follows DNA replication and prepares the cell for division. The cell continues growth, makes division-related proteins, checks whether DNA replication is complete, and responds to damage before entering M phase. This preparation helps reduce the risk of dividing with damaged or incomplete genetic material.
M phase
M phase includes mitosis and cytokinesis in many descriptions. Mitosis separates duplicated chromosomes into two nuclei, while cytokinesis divides the cytoplasm. Together, these processes produce two daughter cells that can begin their own cycles.
Checkpoints and regulators
Cell-cycle checkpoints monitor whether key tasks have been completed. Regulatory proteins such as cyclins and cyclin-dependent kinases help move cells from one phase to the next. If damage or attachment problems are detected, checkpoint pathways can delay progress, trigger repair, or push a damaged cell toward death.
Cancer and runaway division
Cancer is closely tied to cell-cycle control. Mutations that activate growth signals, disable checkpoints, or prevent cell death can let cells divide when they should not. Many cancer treatments target rapidly dividing cells or the signals that drive uncontrolled cycling.
Why it matters
The cell cycle matters because life depends on making new cells at the right time and in the right place. Embryos grow, skin heals, blood cells renew, immune cells expand, and single-celled eukaryotes reproduce through cell-cycle programs. When that regulation fails, the consequences can be developmental, degenerative, or cancerous.