Answer the following eight questions (a through h) based upon a tripeptide seque
ID: 805824 • Letter: A
Question
Answer the following eight questions (a through h) based upon a tripeptide sequence of the following amino acids (one-letter codes are given): S V D T R
a) What is the full name of each of the three amino acids? Spelling counts, but capitalization does not. If one of the answers is an acidic amino acid, use the ate ending instead of the ic acid ending.
b) What is the three-letter code for each of the amino acids?
c) What is the overall charge on the tripeptide at physiological pH (pH 7.4)?
d) For each of the amino acids, is the side chain (R group) hydrophobic, polar but uncharged, positively (+) charged, or negatively (-) charged at physiological pH?
e) What is the overall charge of the tripeptide below pH 1.0?
f) What is the overall charge of the tripeptide at pH 12?
g) What type of intermolecular attractions could the side chains of the amino acids make with the solvent (water) at pH 7.4? (Note that these are attractions with water, not with other amino acids.)
h) If the tripeptide was dissolved in a buffer that is pH 8.5, what would be the net charge on the most abundant chemical species?
Explanation / Answer
Answer
a)
Q--Glutamine neutral. b) Gln
A--Alanine neutral Ala
D--Aspartate.. acidic Asp
c)
at pH =7.4.... charge on Q=0 A=0 and D =-1.
d)
A-hydrophobic...
Q-hydrophilic
D-negatively charged.
e)
at pH =1.. charge on Q=0 . A =0 and D=0.
f) at pH =12.. charge on Q=0 . A =0 and D=-1.
g) the carboxylic side chains lose an H+ ion (proton) and are negative charged.
H2O + H+ => H3O+
hydrogen bonding is present.
h) charge on Q=0 . A =0 and D=-1.
net charge = -1.