Mitosis and Cytokinesis
Mitosis is the division of a duplicated nucleus into two genetically identical daughter nuclei, and cytokinesis is the physical partitioning of the cytoplasm that completes division into two cells. Together they make up the M phase of the cell cycle and ensure that each daughter cell inherits a complete and equal copy of the genome.
Definition
Mitosis is the process by which the replicated chromosomes of a eukaryotic cell are condensed, aligned on a bipolar spindle, and segregated equally into two daughter nuclei; cytokinesis is the subsequent division of the cytoplasm that yields two separate daughter cells.
Scope
The entry describes the ordered stages of mitosis (prophase, prometaphase, metaphase, anaphase, telophase), the assembly and function of the mitotic spindle, the partitioning of the cytoplasm by the contractile ring in animal cells, and how these events are triggered by mitotic CDK activity. It treats mitotic division as a cell-biology topic, not as clinical guidance.
Key concepts
- Prophase, prometaphase, metaphase, anaphase, telophase
- Chromosome condensation
- Mitotic spindle and centrosomes
- Kinetochores and microtubule attachment
- Sister chromatid separation (anaphase)
- Contractile ring and cleavage furrow
- Equal partitioning of the genome
Mechanisms
Entry into mitosis is triggered by activation of the mitotic cyclin-CDK1 complex (the universal mitotic kinase characterised by Nurse), which drives chromosome condensation, nuclear-envelope breakdown, and assembly of the bipolar spindle. Microtubules from the two spindle poles capture sister chromatids at their kinetochores and align them at the metaphase plate; at anaphase the linkages holding sisters together are cleaved and the chromatids are pulled to opposite poles. Cytokinesis then partitions the cytoplasm: in animal cells an actomyosin contractile ring assembles at the cell equator, positioned by signals from the spindle midzone, and constricts to form the cleavage furrow. Glotzer's review sets out the molecular requirements that couple spindle position to furrow formation so that the cut falls between the two segregated genomes.
Clinical relevance
Mitosis underlies tissue growth and renewal, and the mitotic index and abnormal mitotic figures are descriptive features used in tissue analysis. Several anticancer agents are conceptualised as disrupting spindle dynamics in dividing cells. This entry describes division at a reference level and is not a basis for diagnostic or treatment decisions.
History
Mitosis was first described and named in the nineteenth century by Walther Flemming, who observed chromosome movements in stained dividing cells. The molecular triggers were elucidated a century later through work on the mitotic CDK (Nurse) and on the cyclins whose destruction allows exit from mitosis, while the mechanics of cytokinesis were progressively defined through studies of the contractile ring and spindle midzone signalling summarised by Glotzer.
Key figures
- Walther Flemming
- Paul Nurse
- Michael Glotzer
- David Morgan
Related topics
Seminal works
- glotzer-2005
- nurse-1990
- morgan-1997
Frequently asked questions
- What is the difference between mitosis and cytokinesis?
- Mitosis is the division of the nucleus that separates the duplicated chromosomes into two equal sets, while cytokinesis is the separate process that divides the cytoplasm so that two distinct daughter cells are formed; they normally occur in close succession but are mechanistically distinct.
- How does a cell make sure each daughter gets a complete genome?
- Sister chromatids are attached through their kinetochores to microtubules from opposite spindle poles and aligned at the metaphase plate before the linkages are cleaved, so anaphase pulls one complete set of chromatids to each pole; cytokinesis is positioned between the two sets to complete equal partitioning.