A chiral center is a carbon atom in a molecule that has ___ different groups tetrahedrally bonded to it - ANSWERS4
Which amino acid side chain can form a hydrogen bond?
a) Isoleucine
b) alanine
c) glycine
d) threonine - ANSWERSd) threonine
Which amino acid side chain is considered non p...
Chapter 4 stuff Questions & Answers
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A chiral center is a carbon atom in a molecule that has ___ different groups
tetrahedrally bonded to it - ANSWERS4
Which amino acid side chain can form a hydrogen bond?
a) Isoleucine
b) alanine
c) glycine
d) threonine - ANSWERSd) threonine
Which amino acid side chain is considered non polar?
a) Tyrosine
b) Glutamine
c) Isoleucine
d) Histidine - ANSWERSc) Isoleucine
What is the net charge of the predominant form of Arg at:
Which amino acid(s) could be used to make a buffer at pH 4.0?
a) Gln
b)Asp and Gln
c) Asp and Glu
d) Asp
e) Glu - ANSWERSc) Asp and Glu
In order to make a buffer from an amino acid an ionizable side chain is required, and to
make a buffer at pH 4.0 the pKa of that side chain should be approximately 4. Both Asp
and Glu meet this requirement.
, Lysine has pK values of 2.16, 9.06, and 10.54, for its carboxyl, α-amino, and ε-amino
groups, respectively. What is its estimated pI?
a) 5.66
b) 6.85
c) 9.06
d) 9.80 - ANSWERSd) 9.80
The pI of all amino acids except cysteine, lysine, arginine, aspartic acid and glutamic
acid can be estimated by the average of the pK values of the α-amino group and the α-
carboxyl group. For the α-amino acids, pI = 1/2(pKi + pKj) where Ki and Kj are the
dissociation constants of the two ionizations involving the neutral species. For
monoamino, monocarboxylic acids such as glycine, Ki and Kj represent K1 and K2.
However, for aspartic and glutamic acids, Ki and Kj are K1 and KR, whereas for
arginine, histidine, and lysine, these quantities are KR and K2. Thus for lysine (pK1 =
2.16, pK2 = 9.06, pKR = 10.54), pI = 1/2(pKi + pKj) where Ki = KR and Kj = K2: Thus pI
= 1/2(pK2 + pKR) = 1/2(9.06 + 10.54) = 9.80.
What is the net charge at pH 7.0 on a peptide with the sequence?
Ala-Thr-Leu-Asp-Ala-Lys-Pro-Glu
a) +1
b) 0
c) -1
d) +2
e) -2 - ANSWERSc) -1
How many hydrophobic amino acid residues are present in the peptide shown? -
ANSWERS2
The peptide shown has the amino sequence:
a) Val-Ser-Ile-Glu-Lys
b) Lys-Glu-Ile-Ser-Val
c) Val-Asp-Ile-Glu-Lys
d) Thr-Asp-Leu-Gln-Arg - ANSWERSc) Val-Asp-Ile-Glu-Lys
Draw the Ser-His dipeptide at neutral pH. - ANSWERS
Consider the amino acid modifications shown in Figure 4-14:
How would each of them affect the pI of a peptide containing that modified amino acid?
Increase, decrease, or no significant change?
O-Phosphoserine
y-Carboxyglutamate
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