Biochemistry Module 3 Exam (CHEM 210 -
Portage Learning) Questions & Answers
Graded To Pass!!
Q1: Which of the following amino acids has a side chain that is negatively charged at
physiological pH (7.4)?
A. Lysine
B. Arginine
C. Glutamic acid [CORRECT]
D. Histidine
Correct Answer: C
Rationale: Correct because glutamic acid has a side chain carboxyl group with pKa ~4.1;
at pH 7.4, the carboxyl is deprotonated (negatively charged).
Q2: The one-letter abbreviation for the amino acid tryptophan is:
A. W [CORRECT]
B. T
C. Y
D. F
Correct Answer: A
Rationale: Correct because tryptophan uses the one-letter code "W" (derived from its
spelling); this is a standard abbreviation in Portage Learning CHEM 210 biochemistry.
Q3: Which amino acid contains a sulfur atom in its side chain and is capable of forming
disulfide bonds?
A. Methionine
B. Cysteine [CORRECT]
C. Serine
D. Threonine
Correct Answer: B
Rationale: Correct because cysteine contains a thiol (-SH) group in its side chain; two
cysteine residues can oxidize to form a covalent disulfide bridge (-S-S-).
Q4: Calculate the isoelectric point (pI) of an amino acid with pKa1 (α-COOH) = 2.34 and
pKa2 (α-NH₃⁺) = 9.60.
, A. 5.97 [CORRECT]
B. 11.94
C. 7.26
D. 6.94
Correct Answer: A
Rationale: Correct because for amino acids with no ionizable side chain, pI = (pKa1 +
pKa2)/2 = (2.34 + 9.60)/2 = 5.97; the Portage Learning CHEM 210 curriculum emphasizes
this standard calculation.
Q5: At pH 3.0, the predominant form of glutamic acid (pKa α-COOH = 2.19, pKa side chain
= 4.25, pKa α-NH₃⁺ = 9.67) has a net charge of:
A. +1
B. 0
C. -1
D. +2 [CORRECT]
Correct Answer: D
Rationale: Correct because at pH 3.0, the α-COOH is deprotonated (-1), the side chain
COOH is mostly protonated (0), and the α-NH₃⁺ is protonated (+1); net charge = +1 + 0 + (-
1) = +1. Wait, recalculating: α-COOH pKa 2.19, at pH 3.0 it is deprotonated (-1); side chain
pKa 4.25, at pH 3.0 it is protonated (0); α-NH₃⁺ pKa 9.67, at pH 3.0 it is protonated (+1). Net
= -1 + 0 + 1 = 0. Correction: The correct answer should be B. Let me revise:
Q5: At pH 3.0, the predominant form of glutamic acid (pKa α-COOH = 2.19, pKa side chain
= 4.25, pKa α-NH₃⁺ = 9.67) has a net charge of:
A. +1
B. 0 [CORRECT]
C. -1
D. +2
Correct Answer: B
Rationale: Correct because at pH 3.0, the α-COOH (pKa 2.19) is deprotonated (-1), the
side chain carboxyl (pKa 4.25) remains protonated (0), and the α-amino group (pKa 9.67)
is protonated (+1); net charge = -1 + 0 + 1 = 0.
Q6: Which of the following is classified as a basic amino acid?
A. Aspartic acid
B. Glutamic acid
Portage Learning) Questions & Answers
Graded To Pass!!
Q1: Which of the following amino acids has a side chain that is negatively charged at
physiological pH (7.4)?
A. Lysine
B. Arginine
C. Glutamic acid [CORRECT]
D. Histidine
Correct Answer: C
Rationale: Correct because glutamic acid has a side chain carboxyl group with pKa ~4.1;
at pH 7.4, the carboxyl is deprotonated (negatively charged).
Q2: The one-letter abbreviation for the amino acid tryptophan is:
A. W [CORRECT]
B. T
C. Y
D. F
Correct Answer: A
Rationale: Correct because tryptophan uses the one-letter code "W" (derived from its
spelling); this is a standard abbreviation in Portage Learning CHEM 210 biochemistry.
Q3: Which amino acid contains a sulfur atom in its side chain and is capable of forming
disulfide bonds?
A. Methionine
B. Cysteine [CORRECT]
C. Serine
D. Threonine
Correct Answer: B
Rationale: Correct because cysteine contains a thiol (-SH) group in its side chain; two
cysteine residues can oxidize to form a covalent disulfide bridge (-S-S-).
Q4: Calculate the isoelectric point (pI) of an amino acid with pKa1 (α-COOH) = 2.34 and
pKa2 (α-NH₃⁺) = 9.60.
, A. 5.97 [CORRECT]
B. 11.94
C. 7.26
D. 6.94
Correct Answer: A
Rationale: Correct because for amino acids with no ionizable side chain, pI = (pKa1 +
pKa2)/2 = (2.34 + 9.60)/2 = 5.97; the Portage Learning CHEM 210 curriculum emphasizes
this standard calculation.
Q5: At pH 3.0, the predominant form of glutamic acid (pKa α-COOH = 2.19, pKa side chain
= 4.25, pKa α-NH₃⁺ = 9.67) has a net charge of:
A. +1
B. 0
C. -1
D. +2 [CORRECT]
Correct Answer: D
Rationale: Correct because at pH 3.0, the α-COOH is deprotonated (-1), the side chain
COOH is mostly protonated (0), and the α-NH₃⁺ is protonated (+1); net charge = +1 + 0 + (-
1) = +1. Wait, recalculating: α-COOH pKa 2.19, at pH 3.0 it is deprotonated (-1); side chain
pKa 4.25, at pH 3.0 it is protonated (0); α-NH₃⁺ pKa 9.67, at pH 3.0 it is protonated (+1). Net
= -1 + 0 + 1 = 0. Correction: The correct answer should be B. Let me revise:
Q5: At pH 3.0, the predominant form of glutamic acid (pKa α-COOH = 2.19, pKa side chain
= 4.25, pKa α-NH₃⁺ = 9.67) has a net charge of:
A. +1
B. 0 [CORRECT]
C. -1
D. +2
Correct Answer: B
Rationale: Correct because at pH 3.0, the α-COOH (pKa 2.19) is deprotonated (-1), the
side chain carboxyl (pKa 4.25) remains protonated (0), and the α-amino group (pKa 9.67)
is protonated (+1); net charge = -1 + 0 + 1 = 0.
Q6: Which of the following is classified as a basic amino acid?
A. Aspartic acid
B. Glutamic acid
