The following are 2 mcat practice questions. Please tell me what you think the answer is and your logic / some background (if possible).
(1.) The level of active mitotic CDK rises and falls during the cell cycle. Which of the following best explains why the levels of the active mitotic CDK rise?
(a.) Cyclin is degraded by APC, removing MPF inhibition
(b.) Active MPF tht already exists int he cell stimulates APC, which phosphorylates cyclin
(c.) New cyclin is produced, binds CDK, and then undergoes a series of phosphorylation and dephosphorylation reactions to gnerate active CDK
(d.) Checkpoint proteins trigger a MAP kinase cascade which activates transcription factors such as jun, that promote transcription of CDK protein.
(2.) The level of active mitotic CDK rises and falls during the cell cycle. Which of the follwing best explains why the levels of active mitotic CDK fall
(a.) Transcription of cylin stops after activation of p53
(b.) Polyubiquitination of APC triggers degradation of CDK
(c.) Active CDK stimulates a phosphatase that dephosphorylates CDK.
(d.) APC degrades securin, which allows separin to degrade cohesions holding sister chromatids together, which allows anaphase to begin
(e.) Active CDK activates anaphase promoting complex, causing polyubiquitination of cyclin.