Reward: Good Karma

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[SunnySideUp14]

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[phospho]

I could definitely use some good karma... But, dude, didn't you ask the same 2 questions in another thread, which they closed, telling you to do your own homework?

 

[BerkReviewTeach]

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.

MCAT questions only have four choices, which means it would be bad karma to answer questions in an MCAT assistance forum that weren't really MCAT questions. This is one of those Iceland/Greenland conspiracies in terms of good and bad karma, isn't it?

 

[PiBond]

First one is D. Mitogens stimulate Ras which activates the MAP kinase cascade that leads to increased production of Myc and thus increases G1-Cdk activity. Essentially, when conditions for cell proliferation are bueno, signals (see above) stimulate activation of the aforementioned Cdk complex which then stimulates the expression of genes encoding for G1/S and S-cyclins that help us bore through the first checkpoint in the cell cycle.

The second one should be B. APC transfers multiple ubiquitin molecules and thus lead to the degradation via proteasomes of target proteins (cyclins in this case). None of the other answer choices make sense.

When does the karma kick in? I need it tonight if possible

Edit: I think answer choice B should read polyubiquitylation by APC