Question

true or false (explain briefly)

MPF triggers the passage through the spindle assembly checkpoint by catalyzing one or more protein phosphorylation reactions that leads to the formation and activation of the anaphase-promoting complex.

answer:?

Answer 1

Answer:

Mitotic cyclin-dependent kinases (CDKs) control entry into mitosis, but their role during mitotic progression is less well understood. Here we characterize the functions of CDK activity associated with the mitotic cyclins Clb1, Clb2, and Clb3. We show that Clb–CDKs are important for the activation of the ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C)–Cdc20 that triggers the metaphase–anaphase transition. Furthermore, we define an essential role for Clb–CDK activity in anaphase spindle elongation. Thus, mitotic CDKs serve not only to initiate M phase, but are also needed continuously throughout mitosis to trigger key mitotic events such as APC/C activation and anaphase spindle elongation.

Keywords: APC/C, CDK, Cdc20, spindle elongation, mitosis

The purpose of mitosis is the faithful partitioning of the duplicated genome between two daughter cells. Chromosome segregation occurs during anaphase and is triggered by the dissolution of the linkages that hold sister chromatids together (Nasmyth 2002). These linkages are mediated by cohesin complexes, which in budding yeast are composed of Scc1/Mcd1, Scc3, Smc1, and Smc3 (Nasmyth 2002). At the onset of anaphase, the cohesin subunit Scc1/Mcd1 is cleaved by the protease Separase (Esp1 in budding yeast), leading to the loss of cohesion between sister chromatids and subsequent chromosome segregation (Nasmyth 2002). Prior to anaphase, Separase/Esp1 is held inactive by the binding of Securin (Pds1 in budding yeast) (Nasmyth 2002). At the metaphase–anaphase transition, Securin/Pds1 is targeted for proteosomal degradation by an ubiquitin ligase known as the Anaphase-Promoting Complex/Cyclosome (APC/C) and its specificity factor Cdc20 (APC/C–