Question

In a polypeptide at physiologic pH, hydrogen bonding may form between which of the following?

a) side chains of leucine residue and lysine residue
b) side chains of aspartyl residue and glutamyl residue
c) terminal amino acid group and terminal carboxyl group
d) amide group in peptide bond and aspartyl group

This is my thinking. H+ is positive so it would bind to something negative. Lysine is positive so a) would be wrong. Aspartate and glutamate are negative so I'm not too sure about that one. For c) terminal amino acid group has carbon which has a positive change so H wouldn't bind there. And then d) I have no idea.

Answer 1

I agree with you on c.

Answer 2

Apparently the correct answer is in fact d) howevere I don't even understand what d) is means.

Amide:

o=c-nh

Aspartyl:

CH2-COO-

I understand that it may bind to the O- on aspartyl but why would hydrogen binding occur b/t the c-nh when carbon is already bonded to the nitrogen?

Answer 3

It's the H attached to the N that is hydrogen bonded to a negative part; in this case to the CH2COO^-
But c has NH2 on one end and COOH on the other.That's why I picked c.

Answer 4

I'm going to have to ask my prof about this because in lecture she apparently tricked us because we all had chosen C as the answer.

Answer 5

Thank you very much.