The Cell Cycle #lec 2 Flashcards
What does the Cell-Cycle Control System depend on?
The Cell-Cycle Control System depends on cyclically activated Cyclin-Dependent Protein Kinases (Cdks).
How many major classes of cyclins are there?
There are three major classes of cyclins, each defined by the stage of the cell cycle at which they bind Cdks and function.
What inhibits the activity of a cyclin–Cdk complex?
Phosphorylation at a pair of amino acids near the kinase active site inhibits the activity of a cyclin–Cdk complex at certain cell cycle stages.
What inactivates cyclin–Cdk complexes?
Binding of Cdk inhibitor proteins (CKIs) inactivates cyclin–Cdk complexes.
What role do protein phosphatases play in the cell cycle?
Protein phosphatases reverse the effects of Cdks by removing phosphate groups.
Which protein phosphatase is a critical regulator of Cdk substrates?
Protein phosphatase 2A (PP2A) is a particularly critical regulator of Cdk substrates during the cell cycle.
What influences the substrate selectivity of PP2A?
The B subunit influences the substrate selectivity, localization, and regulation of the enzyme.
What is the significance of the ordering of substrate phosphorylation?
The ordering of substrate phosphorylation depends on the activation timing of each cyclin–Cdk complex.
How can the same cyclin–Cdk complex induce different effects?
The same cyclin–Cdk complex can induce different effects at different times in the cycle, indicating that a single enzyme phosphorylates different targets in a specific order.
What factors contribute to the timing of protein phosphorylation?
The timing of protein phosphorylation depends on the opposing phosphatases, each with differing activation times, localization, and affinities for specific targets.
