Summary
Highlights
Our bodies are made of trillions of cells, each following a cell cycle of growth, development, reproduction, and eventual death. Cell division is crucial for replacing old or damaged cells and for growth. While cells in skin and the digestive tract divide frequently, nerve and muscle cells in adults generally do not.
Cells spend about 90% of their life in interphase, performing their specific functions while preparing for division. Interphase consists of three main steps: G1 (first gap), S phase (synthesis), and G2 (second gap). In G1, cells grow and produce proteins and organelles. In S phase, DNA is replicated, forming two copies of genetic information. G2 involves final preparations for division, including the organization of cellular components by centrosomes.
The M phase, shorter than interphase, involves mitosis and cytokinesis. Mitosis is the division of the cell's nucleus, ensuring each new cell receives a complete set of genetic code. Cytokinesis is the division of the cell's cytoplasm, resulting in two separate cells. Animal cells pinch off, while plant cells form a new cell wall.
Mitosis has five smaller steps, remembered by the mnemonic 'Pass Me A Taco, Chef': prophase, metaphase, anaphase, and telophase. Prophase involves DNA condensing into X-shaped chromosomes and the formation of the mitotic spindle. In metaphase, chromosomes align at the cell's center. Anaphase sees sister chromatids separating and moving to opposite poles. Telophase concludes nuclear division, with new nuclear membranes forming around the separated chromosomes.
Cell division is precisely regulated by the cell cycle control system, which uses checkpoints to monitor and control progression through the cycle. These proteins ensure proper DNA replication and chromosome separation. Failure of this system, due to problems in regulatory genes, can lead to uncontrolled cell division, which is characteristic of cancer. Cancer cells bypass normal checkpoints, dividing excessively and disrupting bodily functions.