ACS BIOCHEMISTRY EXAM 300 UNIQUE PRACTICE
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE LATEST UPDATE ALREADY GRADED A+
ASSURED PASS
This ACS Biochemistry Exam study guide provides 300 unique multiple-choice
questions covering buffers, amino acids, protein structure, enzyme kinetics, nucleic
acids, lipids, carbohydrates, metabolism, cofactors, vitamins, and lab techniques.
Organized into nine sections, each question includes four options, the correct
answer, and a detailed rationale. Designed to mirror the American Chemical
Society standardized exam, this resource reinforces core biochemical principles
and problem-solving skills. It complements official ACS study guides and
textbooks like Lehninger or Stryer, helping students prepare effectively for
certification.
Section 1: Buffers, Amino Acids, and Peptides (1–40)
1. A weak acid, HA, has a pKa of 4.11. At pH 7.11, what is the ratio of conjugate
base to acid?
A. 0.001
B. 0.01
C. 100
D. 1000
Answer: D
Rationale: Using the Henderson-Hasselbalch equation: pH = pKa +
log([A⁻]/[HA]). 7.11 = 4.11 + log([A⁻]/[HA]). 3 = log([A⁻]/[HA]), so the ratio is
10³ = 1000.
2. At pH 2.11, the ratio of conjugate base to acid for a weak acid with pKa = 4.11
is:
,A. 0.01
B. 0.1
C. 10
D. 100
Answer: A
Rationale: 2.11 = 4.11 + log([A⁻]/[HA]). −2 = log([A⁻]/[HA]), so the ratio is 10⁻² =
0.01.
3. Which amino acids are negatively charged at physiological pH?
A. Asp and Glu
B. Lys and Arg
C. His and Lys
D. Ser and Thr
Answer: A
Rationale: Aspartate (Asp) and glutamate (Glu) have carboxylic acid side chains
that are deprotonated and negatively charged at pH 7.
4. Which amino acids are positively charged at physiological pH?
A. Asp and Glu
B. Lys, Arg, and His
C. Ser, Thr, and Cys
D. Asn and Gln
Answer: B
Rationale: Lysine (Lys), arginine (Arg), and histidine (His) have side chains that
are protonated and positively charged at physiological pH.
5. Which amino acid contains a sulfur atom?
A. Alanine
B. Glycine
C. Methionine
D. Valine
,Answer: C
Rationale: Methionine contains a sulfur atom in its side chain (thioether group).
6. Which of the following amino acids is classified as an acidic amino acid?
A. Lysine
B. Aspartate
C. Arginine
D. Histidine
Answer: B
Rationale: Aspartate has a carboxylic acid side chain and is classified as acidic.
Lysine and arginine are basic.
7. How many amino acids are classified as nonpolar, aliphatic?
A. 4
B. 5
C. 7
D. 10
Answer: C
Rationale: The nonpolar aliphatic amino acids are Gly, Ala, Val, Leu, Ile, Pro, and
Met (7 total).
8. Which amino acids have aromatic side chains?
A. Phe, Tyr, Trp
B. Leu, Ile, Val
C. Ser, Thr, Cys
D. Asp, Glu, Asn
Answer: A
Rationale: Phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) have aromatic
side chains.
, 9. What is the approximate average molecular mass of an amino acid?
A. 50 Da
B. 110 Da
C. 200 Da
D. 500 Da
Answer: B
Rationale: The average molecular mass of an amino acid residue is approximately
110 Da.
10. Which amino acid does NOT have an ionizable side chain?
A. Asp
B. Cys
C. Lys
D. Asn
Answer: D
Rationale: Asparagine (Asn) has an amide side chain that is not ionizable. Asp,
Cys, and Lys all have ionizable side chains.
11. Which amino acid is classified as having a polar, uncharged R group?
A. Glycine
B. Serine
C. Lysine
D. Phenylalanine
Answer: B
Rationale: Serine has a hydroxyl group in its side chain, making it polar but
uncharged at physiological pH.
12. How many amino acids have ionizable side chains?
A. 3
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALE LATEST UPDATE ALREADY GRADED A+
ASSURED PASS
This ACS Biochemistry Exam study guide provides 300 unique multiple-choice
questions covering buffers, amino acids, protein structure, enzyme kinetics, nucleic
acids, lipids, carbohydrates, metabolism, cofactors, vitamins, and lab techniques.
Organized into nine sections, each question includes four options, the correct
answer, and a detailed rationale. Designed to mirror the American Chemical
Society standardized exam, this resource reinforces core biochemical principles
and problem-solving skills. It complements official ACS study guides and
textbooks like Lehninger or Stryer, helping students prepare effectively for
certification.
Section 1: Buffers, Amino Acids, and Peptides (1–40)
1. A weak acid, HA, has a pKa of 4.11. At pH 7.11, what is the ratio of conjugate
base to acid?
A. 0.001
B. 0.01
C. 100
D. 1000
Answer: D
Rationale: Using the Henderson-Hasselbalch equation: pH = pKa +
log([A⁻]/[HA]). 7.11 = 4.11 + log([A⁻]/[HA]). 3 = log([A⁻]/[HA]), so the ratio is
10³ = 1000.
2. At pH 2.11, the ratio of conjugate base to acid for a weak acid with pKa = 4.11
is:
,A. 0.01
B. 0.1
C. 10
D. 100
Answer: A
Rationale: 2.11 = 4.11 + log([A⁻]/[HA]). −2 = log([A⁻]/[HA]), so the ratio is 10⁻² =
0.01.
3. Which amino acids are negatively charged at physiological pH?
A. Asp and Glu
B. Lys and Arg
C. His and Lys
D. Ser and Thr
Answer: A
Rationale: Aspartate (Asp) and glutamate (Glu) have carboxylic acid side chains
that are deprotonated and negatively charged at pH 7.
4. Which amino acids are positively charged at physiological pH?
A. Asp and Glu
B. Lys, Arg, and His
C. Ser, Thr, and Cys
D. Asn and Gln
Answer: B
Rationale: Lysine (Lys), arginine (Arg), and histidine (His) have side chains that
are protonated and positively charged at physiological pH.
5. Which amino acid contains a sulfur atom?
A. Alanine
B. Glycine
C. Methionine
D. Valine
,Answer: C
Rationale: Methionine contains a sulfur atom in its side chain (thioether group).
6. Which of the following amino acids is classified as an acidic amino acid?
A. Lysine
B. Aspartate
C. Arginine
D. Histidine
Answer: B
Rationale: Aspartate has a carboxylic acid side chain and is classified as acidic.
Lysine and arginine are basic.
7. How many amino acids are classified as nonpolar, aliphatic?
A. 4
B. 5
C. 7
D. 10
Answer: C
Rationale: The nonpolar aliphatic amino acids are Gly, Ala, Val, Leu, Ile, Pro, and
Met (7 total).
8. Which amino acids have aromatic side chains?
A. Phe, Tyr, Trp
B. Leu, Ile, Val
C. Ser, Thr, Cys
D. Asp, Glu, Asn
Answer: A
Rationale: Phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) have aromatic
side chains.
, 9. What is the approximate average molecular mass of an amino acid?
A. 50 Da
B. 110 Da
C. 200 Da
D. 500 Da
Answer: B
Rationale: The average molecular mass of an amino acid residue is approximately
110 Da.
10. Which amino acid does NOT have an ionizable side chain?
A. Asp
B. Cys
C. Lys
D. Asn
Answer: D
Rationale: Asparagine (Asn) has an amide side chain that is not ionizable. Asp,
Cys, and Lys all have ionizable side chains.
11. Which amino acid is classified as having a polar, uncharged R group?
A. Glycine
B. Serine
C. Lysine
D. Phenylalanine
Answer: B
Rationale: Serine has a hydroxyl group in its side chain, making it polar but
uncharged at physiological pH.
12. How many amino acids have ionizable side chains?
A. 3
