WGU C785 BIOCHEMISTRY
COMPREHENSIVE FINAL EXAM 2026
QUESTIONS AND ANSWERS
1. Which amino acid contains a thiol group in its side chain and can form disulfide bonds to
stabilize tertiary protein structure?
A. Cysteine
B. Methionine
C. Serine
D. Proline
Answer: A
Conceptual Explanation: Cysteine contains a reactive sulfhydryl (thiol) group that allows
it to form covalent disulfide bridges with other cysteine residues, which is critical for
tertiary and quaternary structure stability. Methionine contains sulfur but in a thioether
linkage, which does not form disulfide bonds.
2. In the context of enzyme kinetics, what does the Michaelis constant (Km) represent?
A. The concentration of substrate at which the reaction rate is half of Vmax
,B. The maximum velocity of the reaction
C. The turnover number of the enzyme
D. The energy required to reach the transition state
Answer: A
Conceptual Explanation: Km is defined as the substrate concentration at which the
reaction velocity is exactly half of the maximum velocity (Vmax). It serves as an inverse
measure of the enzyme’s affinity for the substrate.
3. A patient presents with metabolic acidosis. Which buffer system is primarily responsible
for maintaining the pH of the extracellular fluid in this individual?
A. Bicarbonate buffer system
B. Protein buffer system
C. Phosphate buffer system
D. Hemoglobin buffer system
Answer: A
Conceptual Explanation: The bicarbonate-carbonic acid system is the most significant
extracellular buffer in the human body, helping to maintain blood pH near 7.4 by managing
CO2 levels through respiration and HCO3- levels through renal excretion.
4. Which of the following describes the ‘Bohr Effect’ regarding hemoglobin?
A. Increased oxygen affinity due to high oxygen partial pressure
, B. Decreased oxygen affinity due to increased CO2 concentration and decreased pH
C. Increased oxygen affinity due to high 2,3-BPG levels
D. Decreased oxygen affinity due to increased pH
Answer: B
Conceptual Explanation: The Bohr Effect refers to the shift in the hemoglobin oxygen-
binding curve to the right in response to increased CO2 or decreased pH, facilitating the
release of oxygen in metabolically active tissues.
5. During DNA replication, which enzyme is responsible for relieving the torsional strain
caused by the unwinding of the double helix?
A. Helicase
B. Primase
C. DNA Ligase
D. Topoisomerase
Answer: D
Conceptual Explanation: Topoisomerases (like DNA gyrase in bacteria) create temporary
breaks in the DNA backbone to relieve supercoiling or torsional strain ahead of the
replication fork created by helicase.
COMPREHENSIVE FINAL EXAM 2026
QUESTIONS AND ANSWERS
1. Which amino acid contains a thiol group in its side chain and can form disulfide bonds to
stabilize tertiary protein structure?
A. Cysteine
B. Methionine
C. Serine
D. Proline
Answer: A
Conceptual Explanation: Cysteine contains a reactive sulfhydryl (thiol) group that allows
it to form covalent disulfide bridges with other cysteine residues, which is critical for
tertiary and quaternary structure stability. Methionine contains sulfur but in a thioether
linkage, which does not form disulfide bonds.
2. In the context of enzyme kinetics, what does the Michaelis constant (Km) represent?
A. The concentration of substrate at which the reaction rate is half of Vmax
,B. The maximum velocity of the reaction
C. The turnover number of the enzyme
D. The energy required to reach the transition state
Answer: A
Conceptual Explanation: Km is defined as the substrate concentration at which the
reaction velocity is exactly half of the maximum velocity (Vmax). It serves as an inverse
measure of the enzyme’s affinity for the substrate.
3. A patient presents with metabolic acidosis. Which buffer system is primarily responsible
for maintaining the pH of the extracellular fluid in this individual?
A. Bicarbonate buffer system
B. Protein buffer system
C. Phosphate buffer system
D. Hemoglobin buffer system
Answer: A
Conceptual Explanation: The bicarbonate-carbonic acid system is the most significant
extracellular buffer in the human body, helping to maintain blood pH near 7.4 by managing
CO2 levels through respiration and HCO3- levels through renal excretion.
4. Which of the following describes the ‘Bohr Effect’ regarding hemoglobin?
A. Increased oxygen affinity due to high oxygen partial pressure
, B. Decreased oxygen affinity due to increased CO2 concentration and decreased pH
C. Increased oxygen affinity due to high 2,3-BPG levels
D. Decreased oxygen affinity due to increased pH
Answer: B
Conceptual Explanation: The Bohr Effect refers to the shift in the hemoglobin oxygen-
binding curve to the right in response to increased CO2 or decreased pH, facilitating the
release of oxygen in metabolically active tissues.
5. During DNA replication, which enzyme is responsible for relieving the torsional strain
caused by the unwinding of the double helix?
A. Helicase
B. Primase
C. DNA Ligase
D. Topoisomerase
Answer: D
Conceptual Explanation: Topoisomerases (like DNA gyrase in bacteria) create temporary
breaks in the DNA backbone to relieve supercoiling or torsional strain ahead of the
replication fork created by helicase.
