Solutions3

Solutions3 - BC368 Biochemistry of the Cell II Problem Set...

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BC368 – Biochemistry of the Cell II Problem Set #3 – Signaling ANSWERS 1 . The fact that the two growth factors together do not raise cAMP levels higher than either growth factor alone tells you that the two growth factors are probably using the same pathway, and that the entire system is probably working to maximum capacity. Because there are no significant differences in the three bars in the graph, about the only thing you can conclude from these data is that the same adenylyl cyclase system is probably used by both growth factors. The two growth factors might be using the same receptor, but further work would need to be done to be sure. 2 . Mutant A must have its mutation in the receptor that binds X, causing it to no longer bind toxin X. The mutation is probably not later in the pathway because the mutant A cells are still susceptible to cholera toxin and pertussis toxin. Because of later data from the mutants below, X must be a toxin that has its effects through a stimulatory pathway. Mutant B must have a mutation in the G s α subunit that results in it always being “turned off” (it cannot stimulate the adenylyl cyclase at all). If the G-protein is always turned off, cholera toxin would have no effect (as our data show!).
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Solutions3 - BC368 Biochemistry of the Cell II Problem Set...

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