WGU C785 BIOCHEMISTRY FINAL
EXAM 2026 QUESTIONS AND ANSWERS
1. Which type of chemical bond is primarily responsible for maintaining the secondary
structure of a protein, such as an alpha-helix or beta-sheet?
A. Disulfide bonds between cysteine residues
B. Hydrogen bonds between the backbone carbonyl oxygen and amide nitrogen
C. Hydrophobic interactions between non-polar side chains
D. Ionic bonds between acidic and basic amino acids
Answer: B
Conceptual Explanation: The secondary structure of a protein is stabilized by hydrogen
bonding between the atoms of the polypeptide backbone, specifically the carbonyl oxygen
and the amide hydrogen.
2. In the context of the Bohr effect, how does an increase in blood CO2 concentration affect
hemoglobin’s affinity for oxygen?
A. It increases oxygen affinity by raising the pH
B. It decreases oxygen affinity by stabilizing the R-state
C. It decreases oxygen affinity by lowering the pH and forming carbamates
,D. It has no effect on hemoglobin but increases myoglobin affinity
Answer: C
Conceptual Explanation: Increased CO2 leads to the production of H+ ions (lowering pH),
which stabilizes the T-state (tense state) of hemoglobin, thereby reducing its affinity for
oxygen and promoting oxygen release to tissues.
3. Which of the following mutations is most likely to result in a non-functional protein?
A. A silent mutation in the third position of a codon
B. A nonsense mutation occurring near the beginning of the coding sequence
C. A missense mutation replacing isoleucine with leucine
D. An expansion of a trinucleotide repeat in a non-coding region
Answer: B
Conceptual Explanation: A nonsense mutation introduces a premature stop codon, which
results in a truncated and usually non-functional protein, especially if it occurs early in the
sequence.
4. What is the primary role of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells?
A. To act as a competitive inhibitor of hexokinase
B. To increase the affinity of hemoglobin for oxygen at high altitudes
C. To stabilize the deoxygenated (T) state of hemoglobin
D. To facilitate the transport of CO2 from tissues to the lungs
, Answer: C
Conceptual Explanation: 2,3-BPG binds to the central cavity of the hemoglobin tetramer
in the T-state, stabilizing it and reducing oxygen affinity, which allows for more efficient
oxygen unloading in peripheral tissues.
5. Which enzyme is the rate-limiting step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
Answer: C
Conceptual Explanation: PFK-1 is the primary rate-limiting enzyme of glycolysis; it is
allosterically regulated by ATP (inhibitor) and AMP/Fructose-2,6-bisphosphate
(activators).
6. During the process of DNA replication, which enzyme is responsible for relieving torsional
strain (supercoiling) ahead of the replication fork?
A. DNA Helicase
B. Topoisomerase
C. DNA Polymerase III
D. DNA Primase
EXAM 2026 QUESTIONS AND ANSWERS
1. Which type of chemical bond is primarily responsible for maintaining the secondary
structure of a protein, such as an alpha-helix or beta-sheet?
A. Disulfide bonds between cysteine residues
B. Hydrogen bonds between the backbone carbonyl oxygen and amide nitrogen
C. Hydrophobic interactions between non-polar side chains
D. Ionic bonds between acidic and basic amino acids
Answer: B
Conceptual Explanation: The secondary structure of a protein is stabilized by hydrogen
bonding between the atoms of the polypeptide backbone, specifically the carbonyl oxygen
and the amide hydrogen.
2. In the context of the Bohr effect, how does an increase in blood CO2 concentration affect
hemoglobin’s affinity for oxygen?
A. It increases oxygen affinity by raising the pH
B. It decreases oxygen affinity by stabilizing the R-state
C. It decreases oxygen affinity by lowering the pH and forming carbamates
,D. It has no effect on hemoglobin but increases myoglobin affinity
Answer: C
Conceptual Explanation: Increased CO2 leads to the production of H+ ions (lowering pH),
which stabilizes the T-state (tense state) of hemoglobin, thereby reducing its affinity for
oxygen and promoting oxygen release to tissues.
3. Which of the following mutations is most likely to result in a non-functional protein?
A. A silent mutation in the third position of a codon
B. A nonsense mutation occurring near the beginning of the coding sequence
C. A missense mutation replacing isoleucine with leucine
D. An expansion of a trinucleotide repeat in a non-coding region
Answer: B
Conceptual Explanation: A nonsense mutation introduces a premature stop codon, which
results in a truncated and usually non-functional protein, especially if it occurs early in the
sequence.
4. What is the primary role of 2,3-bisphosphoglycerate (2,3-BPG) in red blood cells?
A. To act as a competitive inhibitor of hexokinase
B. To increase the affinity of hemoglobin for oxygen at high altitudes
C. To stabilize the deoxygenated (T) state of hemoglobin
D. To facilitate the transport of CO2 from tissues to the lungs
, Answer: C
Conceptual Explanation: 2,3-BPG binds to the central cavity of the hemoglobin tetramer
in the T-state, stabilizing it and reducing oxygen affinity, which allows for more efficient
oxygen unloading in peripheral tissues.
5. Which enzyme is the rate-limiting step of glycolysis?
A. Hexokinase
B. Pyruvate Kinase
C. Phosphofructokinase-1 (PFK-1)
D. Aldolase
Answer: C
Conceptual Explanation: PFK-1 is the primary rate-limiting enzyme of glycolysis; it is
allosterically regulated by ATP (inhibitor) and AMP/Fructose-2,6-bisphosphate
(activators).
6. During the process of DNA replication, which enzyme is responsible for relieving torsional
strain (supercoiling) ahead of the replication fork?
A. DNA Helicase
B. Topoisomerase
C. DNA Polymerase III
D. DNA Primase
