Cyclin - dependent protein kinase 2 (Cdk2) regulates critical events in the prog
ID: 13123 • Letter: C
Question
Cyclin - dependent protein kinase 2 (Cdk2) regulates critical events in the progression of the cell cycle in mammalian cells. Cdk2 can form a complex with A and can be phosphorylated by another protein kinase. CM. to produce P - Cdk2. To determine the roles of cyclin A and phosphorylation in the function of Cdk2. you purify nonphosphorylated and Ctvt - phoephorylatod Cdk2. You mix these tvslo forms of Cdk2 and cyclin A In various combinatory with 32P - ATP and assay for phosphorylation of hrttone Ml (Figure > - 32). You also measure the binding aifinity of various forms of Cdk2 for ATR cyclin A and histone Ml (Table 3 - 4) From Figure 3 - 32, what is required for cdk 2 to phosphorytate histone N1 efficiently? How do the requirements Identified m part A specifically affect the function of Cdk2 relative to its target, hlstone Ht Tl** * - * and Figure 3 - 32)? The usual intracellular concentrations of ATP and AOP are in the range O. t to t mM. Assume that the binding of cyclin a1o Cdk2 or P - Cdk2 does not alter the affinities of either term of Cdk2 for ATP and ADP are important for cdh2 function? Why or why not?Explanation / Answer
a. Cdk2 must form a complex with cyclin A and be phosphorylated in order to phosphorylate histone H1 efficiently. b. Phosphorylation of Cdk2 increases its affinity for ATP and decreases its affinity for ADP. Complexing with cyclin A increases Cdk2's affinity for Histone H1. c. It is not likely that the observed changes in affinity for ATP and ADP are important for Cdk2 function. This is because: a. without the presence of cyclin A, both P-Cdk2 and Cdk2 were unable to effectively phosphorylate Histone H1, and b. the difference in affinity for Histone H1 between Cdk2 and P-Cdk2 when both are in the presence of cyclin A is not significant, as opposed to the difference in affinity between P-Cdk2 and Cdk2 with and without cyclin-A (a difference of about 10x).
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