(Total 6 points) You have isolated a strain of temperature-sensitive mutant yeas
ID: 254813 • Letter: #
Question
(Total 6 points) You have isolated a strain of temperature-sensitive mutant yeast that divides normally at 25°C. However, at 37°C, the mutant pauses in the cell cycle right before M phase. These mutant veast cells are NOT defective in M- Cdk. For each one of the following conditions, state whether or not it could be responsible for the behavior of this strain of yeast (3 points). Explain your reasoning (3 points). A. Inactivation of an enzyme that degrades M-Cyclin. Inactivation of the Wee-1 kinase. Inactivation of the Cdc25 phosphatase B.Explanation / Answer
Answer:-
In condition A, where the Enzyme that degrades M cyclin is inactivated will not cause the cell cycle to pause right before M phase. The reason for it is because M cyclins are the proteins that bind with Cdks and activate them. Now if the enzyme that degrades M cyclin is inactivated then it means that M cyclin will no longer be degraded and it will activate M phase cdks and the cell cycle progression to M phase will carry on normally as it should.
In condition B, if the wee1 kinase is inactivated then also the mitosis will not be paused right before M phase. The function of Wee1 is to phosphorylate the amino acids Tyr15 and Thr14 of Cdk1, which keeps the kinase activity of Cdk1 low and prevents entry into mitosis. If this enzyme is working then the mitosis will be paused but as in this condition wee1 kinase is inactive so it means that cdk activity will be high and cell will enter mitosis.
In condition C, if the cdc25 is inhibited then it will block the the entry of cell to mitosis and in this condition the cell cycle will stop right before M phase. The function of cdc25 phosphatase is the activation of cdks that are responsible for activation of Mcyclins, so if the cdc phosphatase is inactivated it will no lomger be able to activate cdks and in turn the activity of M cyclins will be inhibited, thus causing cell cycle arrest just before M phase.
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