Cell cycle stages and cell growth
Cell biology • Cell division
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The three overall stages of the cell cycle
Interphase → Mitosis → Cytokinesis. Interphase occupies most of the cycle and prepares the cell for division by increasing cell size, replicating DNA and producing extra organelles. Mitosis segregates duplicated chromosomes so each new nucleus receives a full set. Cytokinesis physically separates the cytoplasm and organelles to form two independent daughter cells. Interphase includes metabolic activity required for growth. Mitosis itself is short relative to interphase but essential for equal chromosome allocation. Cytokinesis concludes the cycle by forming cell membranes (and cell walls in plants) around each daughter cell, ensuring separation of cellular contents.
Interphase: growth, DNA replication and organelle increase
Interphase causes growth by active biosynthesis. Protein synthesis and organelle biogenesis increase the number of ribosomes, mitochondria and other sub-cellular structures so that each daughter cell receives sufficient machinery for life. DNA replication during interphase produces exact copies of chromosomes to allow equal segregation later. Limiting factors for interphase activities include availability of nutrients and ATP, fidelity of DNA replication, and surface area-to-volume constraints that affect transport of materials into and out of the cell. Insufficient energy or raw materials slows organelle replication and delays progression to mitosis.
Mitosis: ordered nuclear division
Prophase: Chromosomes condense and the nuclear membrane breaks down, which allows spindle formation and chromosome movement. Metaphase: Chromosomes align at the cell equator because spindle fibres attach to centromeres, which ensures even tension and correct orientation. Anaphase: Sister chromatids separate and move to opposite poles when spindle fibres shorten, producing equal sets of chromosomes at each pole. Telophase: Chromatids reach poles, decondense into chromatin, and new nuclear envelopes form around each set. These steps cause accurate chromosome sorting before the cell splits. Mitosis produces two genetically identical nuclei when chromosome copies separate correctly. Errors in chromosome segregation or DNA replication can cause mutations or abnormal cell function, which underlies some diseases.
Cytokinesis and final partitioning
Cytokinesis follows mitosis and divides the cytoplasm to create two daughter cells. In animal cells, the cell membrane pinches inwards by an actin-based contractile ring until separation completes. In plant cells, a cell plate forms from vesicles at the equator to build new cell walls between daughter cells. Successful cytokinesis ensures that organelles and cytosol distribute between daughters. Failure in cytokinesis produces multinucleated cells or unequal distribution of organelles; such defects impair cell function and tissue integrity. Proper regulation of cytokinesis relies on prior completion of mitosis and sufficient cytoplasmic resources produced during interphase.
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