Mitosis and cytokinesis explained
Cell biology • Cell division
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Key concepts
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Preparation: DNA replication and chromosomal appearance
Interphase precedes mitosis and involves growth and replication of the entire genome so that each chromosome consists of two identical sister chromatids joined at the centromere. Chromosomes shorten and thicken (condense) to allow accurate movement during division. Limiting factor: incomplete or damaged DNA replication prevents correct mitosis and may activate cell-cycle checkpoints.
Chromosome alignment and separation (mitosis stages)
Spindle fibres form between centrosomes and attach to centromeres. Chromosomes line up along the cell equator (metaphase). Spindle microtubules shorten and pull sister chromatids apart towards opposite poles (anaphase). Chromatids arrive at poles and are now individual chromosomes. Nuclear membranes re-form around each chromosome set (telophase). Cause → effect: spindle attachment at centromeres ensures each daughter nucleus receives one complete set of chromosomes.
Cytokinesis: division of cytoplasm and membranes
Cytokinesis separates cytoplasm and cell-surface membrane to produce two distinct cells. In animal cells, the cell membrane pinches inward (cleavage furrow) until the cell splits. In plant cells, a cell plate forms from vesicles at the equator and develops into a new cell wall and membrane, preventing membrane pinching. Cause → effect: structural presence of a rigid cell wall in plants prevents furrowing and requires cell plate formation.
Outcomes and biological roles
Mitosis yields two genetically identical diploid daughter cells with the same chromosome number as the parent. Biological roles include organismal growth, replacement of dead or damaged cells (for example, skin renewal), and asexual reproduction in some species. Uncontrolled mitosis causes abnormal cell masses (tumours). Observation of rapidly dividing stem-cell regions indicates active mitosis.
Recognising mitosis in contexts
Visible indicators of mitosis include condensed, X-shaped chromosomes, disappearance or re-formation of nuclear membranes, and cells with chromosomes aligned or being pulled apart. Microscopy images of root meristems, embryonic tissues or leaf buds often show many cells in mitosis. Cause → effect: tissues with rapid growth or high turnover show higher frequencies of mitotic cells.
Key notes
Important points to keep in mind