SB C/P #38 Change from E-->D amino acid

[betterfuture]

This question does not make sense to me. Aspartate and glutamate are both negatively charged species. Glutamate has a longer chain yet their properties are very much alike.

I don't understand the reasoning of how there are repulsive interactions at play here. Repulsive interactions from what? There was no addition or exclusion of any charges as both are (-) charged. Anyone want to help out?

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[laczlacylaci]

B: E to D doesn't change the charge, so eliminate.
C: From E (glutamic) to D (aspartic) you decrease steric hindrance, so eliminate.
D: increased capacity of the site to act as general base, means increase ability to deprotonate the bound water. Like you said, their properties are alike, so highly doubt this.

A:

(paragraph before table 1) Two negatives create a repulsive interaction->wants to be away from each other->reduced conformational stability.
I didn't really like this question either, I used POE mostly.

 

[aldol16]

I don't know the specifics of the question but two negative charges in one situation are not equivalent to two negative charges in another situation. Take a simple example. Take two point positive charges and put them at infinite separation. They're really not going to interact with one another. Now move them to infinitesimal separation. Now you're going to have a very strong repulsive, Coulombic force - so strong, in fact, that we need one of the four fundamental forces of nature to oppose that repulsive force so that atoms can exist.

Now if you put two negatively-charged residues close to each other (or make a mutation that results in them being closer to each other), that will increase the energy of that conformation.