Problem set 4: Cell cycle control, apoptosis, and the multihit hypothesis Name (
ID: 134404 • Letter: P
Question
Problem set 4: Cell cycle control, apoptosis, and the multihit hypothesis Name (4pts) Xenopus (frog) egg extracts have been used to study the activity of a protein complex called MPF (maturation promoting factor (hint: it is a cdk-c/clin com, 'ex). In these experiments MPF activity correlates with cyclin B protein concentration (see untreoted extract, A). Increase in MPE activity leads to onset of mitosis (very similar to a mammalian cell with cdk-cyclin that we will talk about in class, indicated by the grey rectangles on the graph). Next, researchers added RNAse (degrades RNA) to the extract the result is shown in B. In "C" the RNAse treated extract had additional wild type cyclin RNA added. Finally, in "D" a RNA that codes for a nondegradable protein was added to the extract that had been treated with RNase 1. A.Untreated extract ct MPF activity Cyclin B concentration _ MPF activity ANA Cyclin 8 concentration Time Time C. RNAse treated extract + wild type cyclin B mRNA: D. RNAse treated extract + nondegradable cyclin B mRNA: MPF activity -Cyclin B concentration Cyclin B concentration Time Time a. Why was mitosis not initiated in B of the figure above? Grading rubric(? Consider theoke transat enntheoriint et MPF activity, why does removal o'mRNAfrom the experiment inhibit the cycling of Cyclin 8 protein levels (0.5 points) and MPF activity (0.5 points)?Explanation / Answer
Answer: According to the information, the cyclin-like protein or MPF is essentially required for onset of mitosis. When the cells are deleted out of any MPF and external cdk is added, mitosis continues. But exogenous supply of RNases causes degradation of any cdk-RNA present in the cells, hence any cdk-protein present in the cells and thus, in the absence of both MPF and cdk, cells fail to divide. This is because both sources of initiating mitosis have been removed from the cells, hence cell cycle does not progress.
In all the cases except case B, either an active MPF and/or cdk is present in the cells hence mitosis continues. But in case B, both MPF and cdk are absent/deleted hence mitosis halts.
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