WGU C785 Biochemistry Unit Exam Questions & Answers
Latest 2026 With Complete Solution
SECTION I: PROTEIN STRUCTURE & FUNCTION (Questions 1-20)
Q1: Which level of protein structure is disrupted through the hydrolysis of
peptide bonds?
A) Quaternary
B) Tertiary
C) Secondary
D) Primary
Answer: D) Primary
Rationale: The primary structure of a protein is the linear sequence of amino
acids held together by covalent peptide bonds. Hydrolysis of peptide bonds
breaks these covalent linkages, destroying the primary structure. Secondary,
tertiary, and quaternary structures are dependent on non-covalent
interactions (hydrogen bonds, hydrophobic interactions, ionic bonds) and
disulfide bridges, but these higher-order structures cannot exist without an
intact primary sequence.
Q2: A mutation in the beta-hemoglobin gene results in the replacement of
glutamate (negatively charged, polar) at position 6 with valine (non-polar,
hydrophobic), leading to sickle cell anemia. If the beta hemoglobin gene in a
patient with sickle-cell anemia were edited so that the valine at position 6 was
replaced with a different amino acid, which replacement would be expected to
have the best clinical outcome?
,A) Leucine (non-polar, hydrophobic)
B) Aspartate (negatively charged, polar)
C) Alanine (non-polar, hydrophobic)
D) Glycine (non-polar, hydrophobic)
Answer: B) Aspartate (negatively charged, polar)
Rationale: The original amino acid in a healthy individual is glutamate, which is
negatively charged and polar. The pathologic mutation substitutes valine, a
non-polar, hydrophobic amino acid. This substitution creates a hydrophobic
"sticky" patch on the hemoglobin surface, causing aggregation and sickling. To
restore normal function, the replacement amino acid should most closely
resemble glutamate. Aspartate is also negatively charged and polar, making it
the best theoretical replacement. Other non-polar amino acids would maintain
the hydrophobic patch and likely continue to cause sickling.
Q3: Secondary, tertiary, and quaternary levels of protein structure can all be
impacted by exposing a protein to which treatment?
A) Change of a hydrophobic amino acid to a different hydrophobic amino acid
B) Addition of a reducing agent
C) Placement of the protein in a solution with a low pH
D) Increase in the concentration of the protein in solution
Answer: C) Placement of the protein in a solution with a low pH
Rationale: Changes in pH disrupt hydrogen bonds and ionic bonds throughout
protein structures. Hydrogen bonds in the polypeptide backbone maintain
secondary structure (alpha helices and beta sheets). Hydrogen bonds and ionic
bonds between amino acid side chains maintain tertiary structure. Quaternary
structure, involving interactions between multiple polypeptide subunits, also
relies on these same non-covalent forces. Low pH protonates carboxyl groups
,and other ionizable side chains, disrupting the charge-charge interactions
essential for proper folding and subunit association.
Q4: An increase in beta-pleated sheet structure in some brain proteins can
lead to an increase in amyloid deposit formation, characteristic of
neurodegenerative diseases. What is the primary biochemical process that
follows the increase in beta-pleated sheet structure that leads to the
development of amyloid deposits?
A) An increase in glycogen formation in the brain cells
B) Aggregation of the proteins in the brain
C) Secretion of glucagon, leading to excessive ketogenesis
D) An increase in anaerobic metabolism of glucose in the brain
Answer: B) Aggregation of the proteins in the brain
Rationale: Amyloid deposits result from protein aggregation. The conversion of
normal protein structures to enriched beta-pleated sheet conformations
creates "sticky" surfaces that promote inappropriate protein-protein
interactions. These misfolded proteins aggregate into oligomers, protofibrils,
and mature fibrils that accumulate as insoluble plaques. This pathologic
aggregation is the hallmark of Alzheimer's disease (amyloid-beta plaques),
Parkinson's disease (alpha-synuclein Lewy bodies), Huntington's disease
(polyglutamine aggregates), and prion disorders.
Q5: Which level of protein structure is determined by the sequence of amino
acids?
A) Secondary structure
B) Quaternary structure
, C) Tertiary structure
D) Primary structure
Answer: D) Primary structure
Rationale: The primary structure of a protein is defined as the linear sequence
of amino acids from the N-terminus to the C-terminus, linked by covalent
peptide bonds. This sequence is directly encoded by the nucleotide sequence of
the corresponding gene. All higher levels of protein organization (secondary,
tertiary, quaternary) are ultimately determined by and dependent upon this
primary sequence.
Q6: Which force is most influential in determining the secondary structure of a
protein?
A) Hydrophobic effect
B) Disulfide bonding
C) Hydrogen bonding
D) Electrostatic interactions
Answer: C) Hydrogen bonding
Rationale: Secondary structure (alpha helices and beta sheets) is primarily
stabilized by hydrogen bonds between the backbone carbonyl (C=O) of one
amino acid and the backbone amino (N-H) of another amino acid. These
hydrogen bonds occur at regular intervals along the polypeptide chain,
creating repeating structural patterns. The hydrophobic effect and
electrostatic interactions are more important for tertiary structure. Disulfide
bonds are covalent linkages that stabilize tertiary and quaternary structures
but do not determine secondary structure.
Q7: Which amino acid would most likely participate in hydrogen bonds?
Latest 2026 With Complete Solution
SECTION I: PROTEIN STRUCTURE & FUNCTION (Questions 1-20)
Q1: Which level of protein structure is disrupted through the hydrolysis of
peptide bonds?
A) Quaternary
B) Tertiary
C) Secondary
D) Primary
Answer: D) Primary
Rationale: The primary structure of a protein is the linear sequence of amino
acids held together by covalent peptide bonds. Hydrolysis of peptide bonds
breaks these covalent linkages, destroying the primary structure. Secondary,
tertiary, and quaternary structures are dependent on non-covalent
interactions (hydrogen bonds, hydrophobic interactions, ionic bonds) and
disulfide bridges, but these higher-order structures cannot exist without an
intact primary sequence.
Q2: A mutation in the beta-hemoglobin gene results in the replacement of
glutamate (negatively charged, polar) at position 6 with valine (non-polar,
hydrophobic), leading to sickle cell anemia. If the beta hemoglobin gene in a
patient with sickle-cell anemia were edited so that the valine at position 6 was
replaced with a different amino acid, which replacement would be expected to
have the best clinical outcome?
,A) Leucine (non-polar, hydrophobic)
B) Aspartate (negatively charged, polar)
C) Alanine (non-polar, hydrophobic)
D) Glycine (non-polar, hydrophobic)
Answer: B) Aspartate (negatively charged, polar)
Rationale: The original amino acid in a healthy individual is glutamate, which is
negatively charged and polar. The pathologic mutation substitutes valine, a
non-polar, hydrophobic amino acid. This substitution creates a hydrophobic
"sticky" patch on the hemoglobin surface, causing aggregation and sickling. To
restore normal function, the replacement amino acid should most closely
resemble glutamate. Aspartate is also negatively charged and polar, making it
the best theoretical replacement. Other non-polar amino acids would maintain
the hydrophobic patch and likely continue to cause sickling.
Q3: Secondary, tertiary, and quaternary levels of protein structure can all be
impacted by exposing a protein to which treatment?
A) Change of a hydrophobic amino acid to a different hydrophobic amino acid
B) Addition of a reducing agent
C) Placement of the protein in a solution with a low pH
D) Increase in the concentration of the protein in solution
Answer: C) Placement of the protein in a solution with a low pH
Rationale: Changes in pH disrupt hydrogen bonds and ionic bonds throughout
protein structures. Hydrogen bonds in the polypeptide backbone maintain
secondary structure (alpha helices and beta sheets). Hydrogen bonds and ionic
bonds between amino acid side chains maintain tertiary structure. Quaternary
structure, involving interactions between multiple polypeptide subunits, also
relies on these same non-covalent forces. Low pH protonates carboxyl groups
,and other ionizable side chains, disrupting the charge-charge interactions
essential for proper folding and subunit association.
Q4: An increase in beta-pleated sheet structure in some brain proteins can
lead to an increase in amyloid deposit formation, characteristic of
neurodegenerative diseases. What is the primary biochemical process that
follows the increase in beta-pleated sheet structure that leads to the
development of amyloid deposits?
A) An increase in glycogen formation in the brain cells
B) Aggregation of the proteins in the brain
C) Secretion of glucagon, leading to excessive ketogenesis
D) An increase in anaerobic metabolism of glucose in the brain
Answer: B) Aggregation of the proteins in the brain
Rationale: Amyloid deposits result from protein aggregation. The conversion of
normal protein structures to enriched beta-pleated sheet conformations
creates "sticky" surfaces that promote inappropriate protein-protein
interactions. These misfolded proteins aggregate into oligomers, protofibrils,
and mature fibrils that accumulate as insoluble plaques. This pathologic
aggregation is the hallmark of Alzheimer's disease (amyloid-beta plaques),
Parkinson's disease (alpha-synuclein Lewy bodies), Huntington's disease
(polyglutamine aggregates), and prion disorders.
Q5: Which level of protein structure is determined by the sequence of amino
acids?
A) Secondary structure
B) Quaternary structure
, C) Tertiary structure
D) Primary structure
Answer: D) Primary structure
Rationale: The primary structure of a protein is defined as the linear sequence
of amino acids from the N-terminus to the C-terminus, linked by covalent
peptide bonds. This sequence is directly encoded by the nucleotide sequence of
the corresponding gene. All higher levels of protein organization (secondary,
tertiary, quaternary) are ultimately determined by and dependent upon this
primary sequence.
Q6: Which force is most influential in determining the secondary structure of a
protein?
A) Hydrophobic effect
B) Disulfide bonding
C) Hydrogen bonding
D) Electrostatic interactions
Answer: C) Hydrogen bonding
Rationale: Secondary structure (alpha helices and beta sheets) is primarily
stabilized by hydrogen bonds between the backbone carbonyl (C=O) of one
amino acid and the backbone amino (N-H) of another amino acid. These
hydrogen bonds occur at regular intervals along the polypeptide chain,
creating repeating structural patterns. The hydrophobic effect and
electrostatic interactions are more important for tertiary structure. Disulfide
bonds are covalent linkages that stabilize tertiary and quaternary structures
but do not determine secondary structure.
Q7: Which amino acid would most likely participate in hydrogen bonds?
