PATHOLOGY MCQ
CELL DAMAGE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Changing concentrations of cdk result in binding to cyclin
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Changing concentrations of cyclin affect the level of MPF
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MPF complex formation decreases with increased cdk levels
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MPF complex formation decreases with increased cyclin levels
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Detailed explanation-1: -Cdk is present at a constant level, but Cyclin’s concentration gradually increases and then sharply decreases. The increase and decrease of cyclin impacts directly the concentration of MPF, which allows the cell to pass the G2 checkpoint when its concentration is high enough.
Detailed explanation-2: -Because the kinase activity of MPF requires cyclin, it tracks the rise in cyclin near the end of the G2, and its fall after mitosis. Cyclin begins to accumulate in G1, rising gradually and binding to more and more cdk subunits. MPF reaches a threshold concentration in G2 that triggers entry into mitosis.
Detailed explanation-3: -Maturation promoting factor (MPF) serves as a G2 checkpoint and helps regulate the passage from the G2 to M phase. When both cylin and cyclin dependent kinase (Cdk) are present at the end of the G2 stage, they form a complex of MPF, which facilitates the transition to the M phase.
Detailed explanation-4: -Increases in the concentration of cyclin proteins are triggered by both external and internal signals. After the cell moves to the next stage of the cell cycle, the cyclins that were active in the previous stage are degraded. Cyclins regulate the cell cycle only when they are tightly bound to Cdks.