Problem Set 5 answer key 1. 1 pt. Order: C-A-B 4 pts Justifications: Mutant A- calcium release cannot be activated even in the presence of non-hydrolyzable IP3, so the problem is probably in the calcium channel itself. Mutant B- Calcium release is triggered in both experiments, but gene expression is not observed. This indicates something wrong downstream of calcium release. Mutant C- no effect is observed unless IP3 is added. Probably something wrong with the receptor or PLC, such that PIP2 is never cleaved to produce IP3 and DAG. Functions: C could be the receptor or PLCg, A is probably the Calcium channel, and B is PKC or any transcription factor targets. 2. A) 3 pts. • Protein X is a substrate of APC • Accordingly, at the onset of anaphase, it becomes polyubiquitinated, producing higher molecular weight versions of Protein X. • The polyubiquitination targets Protein X for degradation by the proteosome. • Thus, in telophase, no Protein X remains to be detected by western blot.
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