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| Description: Mitosis is traditionally subdivided into five consecutive and morphologically distinct phases: prophase, prometaphase, metaphase, anaphase and telophase. To enter mitosis, the cell requires the activity of he tmaster mitotic kinase, cyclin-dependent kinase-1 (CDK1), which depends strictly on the binding of cyclin B to CDK1. Separase is a protease, the activity of which is required to remove sister-chromatid cohesion at the metaphase-toanaphase transition (cohesin is indicated in yellow on the expanded view of the chromosome). Prior to anaphase, separase is kept inactive by the binding of a protein known as securin (SEC). Unattached kinetochores (red hemi-circles) contribute to the creation of the mitotic checkpoint complex (MCC), which inhibits the ability of CDC20 to activate the anaphase-promoting complex/cyclosome (APC/C). The attachment of all sister-kinetochore pairs to kinetochore microtubules, and their bi-orientation  which produces congression to the spindle equator  negatively regulates the spindle-assembly checkpoint (SAC) signal. This releases CDC20, which can now activate the APC/C. This results in the polyubiquitylation of anaphase substrates such as cyclin B and securin, and their subsequent proteolytic destruction by the proteasome. The degradation of SEC results in the activation of separase, which targets the cohesin ring that is holding the sister chromatids together, thus causing the loss of sister-chromatid cohesion and the separation of sister chromatids. The degradation of cyclin B at this stage also inactivates the master mitotic kinase CDK1–cyclin B, initiating cytokinesis and the mitotic-exit programme. Attached kinetochores are shown in green.
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