Question

In the spindle assembly checkpoint of cell division: In the absence of ______, there is a protein called securin that binds and activates separase which destroys cohesin rings.

Answer 1

The correct functioning of the spindle assembly checkpoint during cell division ensures that separase is activated through the degradation of securin and consequently cleaves cohesin, allowing sister chromatids to separate and ensuring proper cell division.

Step-by-step explanation:

In the spindle assembly checkpoint of cell division, the absence of proper attachment of chromosomes to the mitotic spindle can prevent the anaphase stage from proceeding. When chromosomes are correctly aligned and attached, tension is created, which leads to the activation of separase, an enzyme that then cleaves cohesin proteins. This cleavage allows sister chromatids to separate and migrate to opposite poles. When separase is inactive, due to the binding of securin, cohesin rings maintain the connection between sister chromatids. It is only when the tension thresholds at the spindle apparatus are achieved that securin is degraded, separase is activated, and the chromatids are allowed to separate, facilitating anaphase and leading on to cytokinesis where the nucleus reforms and the cell divides.