Cellecyklusens

Cellecyklusens, in English the cell cycle, denotes the series of events by which a eukaryotic cell grows, replicates its DNA, and divides. The cycle coordinates cellular growth, genome duplication, and cell division to produce two new cells with an identical genetic complement. Some cells may exit the cycle temporarily or permanently, entering a quiescent state known as G0.

Interphase comprises G1, S, and G2. During G1, cells grow and carry out routine metabolism; in S phase DNA is replicated and sister chromatids are formed; in G2 cells assess DNA integrity and prepare for mitosis. The centrosome duplicates, and cell size increases in preparation for division.

M phase and cytokinesis: M phase includes mitosis (prophase to telophase) and cytokinesis. During mitosis, chromosomes condense, align at the metaphase plate, and separate into two sets. Cytokinesis divides the cytoplasm, yielding two distinct daughter cells. In animal cells a contractile actomyosin ring creates a cleavage furrow; in many plant cells vesicles form a cell plate that becomes a separating cell wall.

Regulation: Progression through the cell cycle is controlled by cyclin-dependent kinases (CDKs) activated by cyclins. Checkpoints at G1/S, G2/M, and the spindle assembly checkpoint monitor DNA integrity, cell size, and proper chromosome attachment. Tumor suppressors such as p53 and Rb influence checkpoint decisions. External signals, such as growth factors and nutrient availability, modulate entry into and exit from the cycle.

Variations and related processes: While the mitotic cell cycle is conserved in many eukaryotes, some cells enter G0 and remain there for extended periods. Meiosis is a related, but distinct, division that produces haploid gametes and involves two consecutive divisions and different regulatory controls.