Indicate whether each of the following, when active, tends to activate (A) or inactivate (I) M-Cdks. The correct answer will be a four-letter string composed of letters A and I only, e. g. IIAI.

( A ) M-Cdk
( I ) Cdc20–APC/C
( I ) Cdh1–APC/C
( I ) Wee1

AIII

Explanation:

Cell cycle is mainly divided into two phases-Interphase and Mitotic phaseInterphase is the preparatory phase whereas mitotic phase is the dividing phaseVarious cyclins and Cdks are regulated during these phasesM-Cdks stands for Mitotic Cyclin Dependent Kinases which helps in cell cycle regulationCdks are the catalytic subunit bound to the regulatory subunit(cyclins)Mitosis includes four stage namely Prophase,Metaphase,Anaphase and TelophaseDuring the Anaphase stage separation of sister chromatids occurs due to the destruction of a protein called cohesinDestruction of cohesin is catalysed by an enzyme called separasePrior to anaphase securin binds to separase and inhibits its activityThe APC(anaphase promoting complex) with specificity factor Cdc20 tragets securin for polyubiquitination which then degraded by proteasomeThe separase released becomes active and breaks the bridge between sister chromatids Movement of sister chromatids occurs towards their respective polesIn late anaphase,specific phopshates called Cdc14 removes the regulatory phosphate group from cdh1 specificity factor and therefore Cdh1 becomes activeActive Cdh1 specificity factor binds to and activate APC(anaphase promoting complex)Cdh1 bound APC catalyse ubiquitination of mitotic cyclinsAs the mitotic cyclins are degraded by the proteasome,onset of telophase startsWee1 is a kinase enzyme which comes into consideration in case of fission yeastWee 1 phosphorylates the inhibitory site of M-Cdk which further leads the cells to enter into mitosis

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