Tripeptide sequence N I R e What is the overall charge of th

Tripeptide sequence: N I R

e) What is the overall charge of the most abundant tripeptide species below pH 1.0?

f) What is the overall charge of the most abundant tripeptide species at pH 11.5?

g) What type of intermolecular force could the side chains form with water? (Note that these are interactions are with water, not with other amino acids.)

(Chose 1) - Hydrophobic interactions - ionic interactions - hydrogen bonds

Please show your work. Thank you!

Solution

e)When the pH=1 then the carbonyl group on lysine in the NIR sequence is protonated, making the charge +2 overall.

f)At pH=11.5 the amino group in tri-peptide will disassociate which helps in making a 50:50 mixture of +1 and -1 .Howvever the buffer is below that along with fact that the physiological pH of 7.4 is very close to the pH of this buffer and the charge at that pH is +1 .The overall charge is +1 in this case.

g)The answer is hydrogen bonds because Water has has a hydrogen which is bound to an oxygen .The oxygen present here is much more electronegative than hydrogen.As a result the oxygen does not sharethose bonded electrons very nicely.This leads to the formation of dipoles of a special type called hydrogen bonds.