WGU C785 Biochemistry Unit Exam
2026/2027
Instructions: Choose the best answer for each of the following multiple-choice questions. The
questions are designed to test your knowledge of key biochemical principles, including the structure
and function of biomolecules, enzyme kinetics, metabolic pathways, and the central dogma of
molecular biology.
Section 1: Amino Acids and Protein Structure (Questions 1-25)
1. Which of the following amino acids is classified as nonpolar and hydrophobic?
A. Lysine
B. Aspartate
C. Valine
D. Serine
Answer: C
Rationale: Valine has an aliphatic isopropyl side chain, making it nonpolar and hydrophobic. Lysine and
aspartate are charged (basic and acidic, respectively), and serine is polar uncharged.
,2. At a physiological pH of 7.4, the amino acid aspartate would have a net charge of:
A. +1
B. 0
C. -1
D. -2
Answer: C
Rationale: Aspartate has an alpha-carboxyl group (pKa ~2), an alpha-amino group (pKa ~9.6), and an
acidic side chain (pKa ~3.9). At pH 7.4, both the alpha-carboxyl and the side chain are deprotonated (-1
each), and the alpha-amino group is protonated (+1). The net charge is (+1) + (-1) + (-1) = -1.
3. A peptide bond is formed between the:
A. R-group of one amino acid and the amino group of another.
B. Carboxyl group of one amino acid and the amino group of another.
C. Carboxyl group of one amino acid and the R-group of another.
D. Amino group of one amino acid and the amino group of another.
Answer: B
Rationale: A peptide bond is an amide linkage specifically formed by a dehydration (condensation)
reaction between the alpha-carboxyl group of one amino acid and the alpha-amino group of the next.
4. Which level of protein structure is primarily stabilized by hydrogen bonds between the carbonyl
oxygen and amide hydrogen of the polypeptide backbone?
A. Primary
B. Secondary
C. Tertiary
,D. Quaternary
Answer: B
Rationale: Secondary structure, which includes alpha-helices and beta-sheets, is stabilized by regular
hydrogen bonding between atoms of the polypeptide backbone, not the R-groups.
5. Sickle cell anemia is caused by a mutation that replaces a glutamate residue with a valine residue in
the beta-globin chain. This is an example of a change in which level of protein structure?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary
Answer: A
Rationale: The mutation changes the amino acid sequence of the polypeptide chain. The primary
structure is the specific sequence of amino acids.
6. The unfolding and loss of a protein's three-dimensional shape, often caused by heat or changes in pH,
is called:
A. Hydrolysis
B. Denaturation
C. Oxidation
D. Reduction
Answer: B
Rationale: Denaturation is the process where a protein loses its native secondary, tertiary, and
quaternary structure, typically rendering it non-functional.
, 7. Which amino acid is known for disrupting alpha-helical structures due to its rigid ring structure?
A. Glycine
B. Alanine
C. Proline
D. Leucine
Answer: C
Rationale: Proline has a cyclic structure where its side chain bonds back to the backbone nitrogen. This
restricts rotation around the N-Cα bond and introduces a kink, disrupting the regular pattern of an
alpha-helix.
8. The interaction between a positively charged lysine residue and a negatively charged aspartate
residue in a protein's tertiary structure is an example of a(n):
A. Hydrogen bond
B. Hydrophobic interaction
C. Disulfide bond
D. Ionic bond (salt bridge)
Answer: D
Rationale: An ionic bond, or salt bridge, is a strong electrostatic attraction between two oppositely
charged groups.
9. Which of the following is a post-translational modification that can regulate protein activity?
A. Transcription
B. Translation
C. Phosphorylation
2026/2027
Instructions: Choose the best answer for each of the following multiple-choice questions. The
questions are designed to test your knowledge of key biochemical principles, including the structure
and function of biomolecules, enzyme kinetics, metabolic pathways, and the central dogma of
molecular biology.
Section 1: Amino Acids and Protein Structure (Questions 1-25)
1. Which of the following amino acids is classified as nonpolar and hydrophobic?
A. Lysine
B. Aspartate
C. Valine
D. Serine
Answer: C
Rationale: Valine has an aliphatic isopropyl side chain, making it nonpolar and hydrophobic. Lysine and
aspartate are charged (basic and acidic, respectively), and serine is polar uncharged.
,2. At a physiological pH of 7.4, the amino acid aspartate would have a net charge of:
A. +1
B. 0
C. -1
D. -2
Answer: C
Rationale: Aspartate has an alpha-carboxyl group (pKa ~2), an alpha-amino group (pKa ~9.6), and an
acidic side chain (pKa ~3.9). At pH 7.4, both the alpha-carboxyl and the side chain are deprotonated (-1
each), and the alpha-amino group is protonated (+1). The net charge is (+1) + (-1) + (-1) = -1.
3. A peptide bond is formed between the:
A. R-group of one amino acid and the amino group of another.
B. Carboxyl group of one amino acid and the amino group of another.
C. Carboxyl group of one amino acid and the R-group of another.
D. Amino group of one amino acid and the amino group of another.
Answer: B
Rationale: A peptide bond is an amide linkage specifically formed by a dehydration (condensation)
reaction between the alpha-carboxyl group of one amino acid and the alpha-amino group of the next.
4. Which level of protein structure is primarily stabilized by hydrogen bonds between the carbonyl
oxygen and amide hydrogen of the polypeptide backbone?
A. Primary
B. Secondary
C. Tertiary
,D. Quaternary
Answer: B
Rationale: Secondary structure, which includes alpha-helices and beta-sheets, is stabilized by regular
hydrogen bonding between atoms of the polypeptide backbone, not the R-groups.
5. Sickle cell anemia is caused by a mutation that replaces a glutamate residue with a valine residue in
the beta-globin chain. This is an example of a change in which level of protein structure?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary
Answer: A
Rationale: The mutation changes the amino acid sequence of the polypeptide chain. The primary
structure is the specific sequence of amino acids.
6. The unfolding and loss of a protein's three-dimensional shape, often caused by heat or changes in pH,
is called:
A. Hydrolysis
B. Denaturation
C. Oxidation
D. Reduction
Answer: B
Rationale: Denaturation is the process where a protein loses its native secondary, tertiary, and
quaternary structure, typically rendering it non-functional.
, 7. Which amino acid is known for disrupting alpha-helical structures due to its rigid ring structure?
A. Glycine
B. Alanine
C. Proline
D. Leucine
Answer: C
Rationale: Proline has a cyclic structure where its side chain bonds back to the backbone nitrogen. This
restricts rotation around the N-Cα bond and introduces a kink, disrupting the regular pattern of an
alpha-helix.
8. The interaction between a positively charged lysine residue and a negatively charged aspartate
residue in a protein's tertiary structure is an example of a(n):
A. Hydrogen bond
B. Hydrophobic interaction
C. Disulfide bond
D. Ionic bond (salt bridge)
Answer: D
Rationale: An ionic bond, or salt bridge, is a strong electrostatic attraction between two oppositely
charged groups.
9. Which of the following is a post-translational modification that can regulate protein activity?
A. Transcription
B. Translation
C. Phosphorylation
