Multiple Choice
Which of the following cell cycle checkpoints occurs immediately before the start of S phase?
16. Cell Division
Control of the Cell Cycle
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Which of the following proteins is responsible for removing the inhibitory phosphate on Cdks?
A
S cyclins
B
APC
C
M cyclins
D
Cdc25
Verified step by step guidance1
Understand the role of Cdks (Cyclin-dependent kinases) in the cell cycle. Cdks are crucial for the regulation of the cell cycle, and their activity is controlled by phosphorylation and dephosphorylation.
Recognize that Cdks are initially inactive when bound to cyclins due to an inhibitory phosphate group. This phosphate must be removed for the Cdk to become active and drive the cell cycle forward.
Identify the role of Cdc25 phosphatase. Cdc25 is a phosphatase enzyme that specifically removes the inhibitory phosphate from Cdks, thereby activating them.
Differentiate between the roles of S cyclins, M cyclins, and APC. S cyclins and M cyclins bind to Cdks to form active complexes, while APC (Anaphase Promoting Complex) is involved in marking proteins for degradation, not in dephosphorylation.
Conclude that Cdc25 is the protein responsible for removing the inhibitory phosphate on Cdks, allowing them to become active and progress the cell cycle.
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