got another one (sorry just took this today...)
i understand why the Z conformation is possible given the data, but what excludes the A conformation... doesn't the observed helical twist fall well within its range?
Sorry for the delayed response. But I think I know what you're referring to and the answer is that the other two angles are too large to fall within the 30 degree angle of the 12 amino acids that form the 360 helix. 360/12 = 30 degrees, only Z falls in that range.
and for maluskeeter
There is one thing you should know about reduction potentials that would've helped you nail this question in a heartbeat. Copper has a positive reduction, which means it would have a tendency of being reduced. Zinc and Lead both have negative potentials, which in the scheme of things, have a better potential of being oxidized (flip the equation and you get the positive E). Silver, like Copper, has a positive E which means it, too, would want to get reduced.
All E measures is the tendency of an element to be reduced. If it has a larger positive value for the reduction potential, then it would spontaneously reduce into Copper instead of oxidizing to a Copper ion(The reverse).
G =
-nFE. From there, we can find just how reluctant an element is to be reduced. A more positive E = a more negative deltaG - spontaneous.
Taking that into account, what the question basically asks, is for you to find which of the 3 elements would work with Copper to help Copper be reduced while they become oxidized. Subtracting their values from Copper (which upon noticing, you did the reverse) basically gives X = Cu - Y. With Y being the element's E and X being the total. If X yields a positive value, then you have a working galvonic cell which would have Copper being reduced and the other element being oxidized. Silver wouldn't work because it would yield a negative value and instead favors the oxidation of Copper and the reduction of Silver ions.
A positive E - favors reduction. A negative E - favors oxidation