CHEM 210 BIOCHEMISTRY MODULE 2 EXAM ACTUAL
2026/2027 | Protein Function: Hemoglobin, Myoglobin &
Enzyme Catalysis | Geneva College | Complete Questions &
Verified Answers | Pass Guaranteed - A+ Graded
Section 1: Myoglobin & Hemoglobin Structure (Q1-12)
Q1. Myoglobin is a monomeric oxygen-binding protein found in muscle tissue. How
many amino acid residues does the single polypeptide chain of myoglobin contain?
A. 141 amino acid residues
B. 146 amino acid residues
C. 153 amino acid residues
D. 158 amino acid residues
C. 153 amino acid residues [CORRECT]
Rationale: Myoglobin consists of a single polypeptide chain of 153 amino acids with
one heme prosthetic group, whereas the α-chain of hemoglobin contains 141 residues
and the β-chain contains 146 residues.
Correct Answer: C
Q2. A patient presents with carbon monoxide poisoning. The emergency physician
explains that the distal histidine (E7) in hemoglobin provides critical protection against
CO toxicity. Which statement best describes this protective biochemical function?
A. The distal histidine increases CO binding affinity by 20,000-fold compared to free
heme
B. The distal histidine prevents Fe²⁺ oxidation to Fe³⁺ and reduces CO binding affinity
through steric hindrance and hydrogen bonding
,C. The distal histidine directly cleaves CO molecules in the bloodstream
D. The distal histidine stabilizes the R-state to prevent any CO binding whatsoever
B. The distal histidine prevents Fe²⁺ oxidation to Fe³⁺ and reduces CO binding affinity
through steric hindrance and hydrogen bonding [CORRECT]
Rationale: The distal histidine (E7) helps prevent oxidation of ferrous iron (Fe²⁺) to ferric
iron (Fe³⁺) and provides steric hindrance that reduces CO binding from approximately
20,000-fold preference (free heme) to approximately 200-fold (hemoglobin), while also
hydrogen bonding to bound O₂.
Correct Answer: B
Q3. In the heme prosthetic group of both myoglobin and hemoglobin, the iron atom
(Fe²⁺) is coordinated in an octahedral geometry. Which molecules or residues serve as
the six ligands?
A. Four histidine nitrogens, one proximal histidine, and one oxygen ligand
B. Four pyrrole nitrogens, one proximal histidine (His F8), and one O₂/CO ligand
C. Two cysteine sulfurs, three pyrrole nitrogens, and one oxygen ligand
D. Six pyrrole nitrogens with no protein-derived ligands
B. Four pyrrole nitrogens, one proximal histidine (His F8), and one O₂/CO ligand
[CORRECT]
Rationale: The heme iron is coordinated by four nitrogen atoms from the protoporphyrin
IX ring, the imidazole nitrogen of the proximal histidine (His F8) as the fifth ligand, and
either O₂ or CO as the sixth (reversible) ligand.
Correct Answer: B
,Q4. A biochemistry student is examining the structural changes that occur upon oxygen
binding to hemoglobin. In the deoxy (T) state, the Fe²⁺ ion is positioned approximately
0.4 Å out of the heme plane toward the proximal histidine. Upon oxygen binding and
transition to the R-state:
A. Fe²⁺ remains out of the heme plane to maintain low oxygen affinity
B. Fe²⁺ moves into the heme plane, triggering conformational changes that propagate to
other subunits
C. Fe²⁺ is oxidized to Fe³⁺ and dissociates from the heme group
D. Fe²⁺ moves further out of the plane toward the distal histidine
B. Fe²⁺ moves into the heme plane, triggering conformational changes that propagate to
other subunits [CORRECT]
Rationale: When O₂ binds, the Fe²⁺ atom moves into the plane of the porphyrin ring,
pulling the F-helix and proximal histidine with it; this movement triggers the breaking of
salt bridges and the T→R quaternary transition that increases affinity in remaining
subunits.
Correct Answer: B
Q5. A researcher measures oxygen binding curves for purified myoglobin and adult
hemoglobin at pH 7.4 in the presence of physiological 2,3-BPG. Which of the following
correctly describes the expected binding curves and P₅₀ values?
A. Both proteins show hyperbolic curves with P₅₀ values near 26 torr
B. Myoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; hemoglobin shows a
sigmoidal curve with P₅₀ ~26 torr
C. Both proteins show sigmoidal curves, but myoglobin has a lower P₅₀ than
hemoglobin
D. Hemoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; myoglobin shows a
sigmoidal curve with P₅₀ ~26 torr
, B. Myoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; hemoglobin shows a
sigmoidal curve with P₅₀ ~26 torr [CORRECT]
Rationale: Myoglobin is monomeric and exhibits non-cooperative binding with a
hyperbolic curve and high affinity (low P₅₀ ~2-3 torr), whereas hemoglobin's tetrameric
structure produces cooperative binding with a sigmoidal curve and lower affinity (P₅₀
~26 torr) under physiological conditions.
Correct Answer: B
Q6. A newborn is found to have a hemoglobin variant with higher oxygen affinity than
maternal hemoglobin. Electrophoretic analysis reveals the presence of γ-subunits
containing serine at position 143 instead of histidine. This hemoglobin variant is:
A. Hemoglobin S (sickle cell hemoglobin)
B. Hemoglobin A₂ (minor adult hemoglobin)
C. Hemoglobin F (fetal hemoglobin)
D. Hemoglobin A (adult hemoglobin)
C. Hemoglobin F (fetal hemoglobin) [CORRECT]
Rationale: Hemoglobin F (α₂γ₂) is the major fetal hemoglobin; the γ-subunit has serine at
position 143 (instead of histidine in the β-chain), which reduces positive charge in the
central cavity and weakens 2,3-BPG binding, resulting in higher oxygen affinity
(left-shifted curve) that facilitates placental oxygen transfer.
Correct Answer: C
Q7. Adult hemoglobin (HbA) exhibits a specific quaternary structure essential for
cooperative oxygen binding. Which subunit composition and arrangement correctly
describes HbA?
2026/2027 | Protein Function: Hemoglobin, Myoglobin &
Enzyme Catalysis | Geneva College | Complete Questions &
Verified Answers | Pass Guaranteed - A+ Graded
Section 1: Myoglobin & Hemoglobin Structure (Q1-12)
Q1. Myoglobin is a monomeric oxygen-binding protein found in muscle tissue. How
many amino acid residues does the single polypeptide chain of myoglobin contain?
A. 141 amino acid residues
B. 146 amino acid residues
C. 153 amino acid residues
D. 158 amino acid residues
C. 153 amino acid residues [CORRECT]
Rationale: Myoglobin consists of a single polypeptide chain of 153 amino acids with
one heme prosthetic group, whereas the α-chain of hemoglobin contains 141 residues
and the β-chain contains 146 residues.
Correct Answer: C
Q2. A patient presents with carbon monoxide poisoning. The emergency physician
explains that the distal histidine (E7) in hemoglobin provides critical protection against
CO toxicity. Which statement best describes this protective biochemical function?
A. The distal histidine increases CO binding affinity by 20,000-fold compared to free
heme
B. The distal histidine prevents Fe²⁺ oxidation to Fe³⁺ and reduces CO binding affinity
through steric hindrance and hydrogen bonding
,C. The distal histidine directly cleaves CO molecules in the bloodstream
D. The distal histidine stabilizes the R-state to prevent any CO binding whatsoever
B. The distal histidine prevents Fe²⁺ oxidation to Fe³⁺ and reduces CO binding affinity
through steric hindrance and hydrogen bonding [CORRECT]
Rationale: The distal histidine (E7) helps prevent oxidation of ferrous iron (Fe²⁺) to ferric
iron (Fe³⁺) and provides steric hindrance that reduces CO binding from approximately
20,000-fold preference (free heme) to approximately 200-fold (hemoglobin), while also
hydrogen bonding to bound O₂.
Correct Answer: B
Q3. In the heme prosthetic group of both myoglobin and hemoglobin, the iron atom
(Fe²⁺) is coordinated in an octahedral geometry. Which molecules or residues serve as
the six ligands?
A. Four histidine nitrogens, one proximal histidine, and one oxygen ligand
B. Four pyrrole nitrogens, one proximal histidine (His F8), and one O₂/CO ligand
C. Two cysteine sulfurs, three pyrrole nitrogens, and one oxygen ligand
D. Six pyrrole nitrogens with no protein-derived ligands
B. Four pyrrole nitrogens, one proximal histidine (His F8), and one O₂/CO ligand
[CORRECT]
Rationale: The heme iron is coordinated by four nitrogen atoms from the protoporphyrin
IX ring, the imidazole nitrogen of the proximal histidine (His F8) as the fifth ligand, and
either O₂ or CO as the sixth (reversible) ligand.
Correct Answer: B
,Q4. A biochemistry student is examining the structural changes that occur upon oxygen
binding to hemoglobin. In the deoxy (T) state, the Fe²⁺ ion is positioned approximately
0.4 Å out of the heme plane toward the proximal histidine. Upon oxygen binding and
transition to the R-state:
A. Fe²⁺ remains out of the heme plane to maintain low oxygen affinity
B. Fe²⁺ moves into the heme plane, triggering conformational changes that propagate to
other subunits
C. Fe²⁺ is oxidized to Fe³⁺ and dissociates from the heme group
D. Fe²⁺ moves further out of the plane toward the distal histidine
B. Fe²⁺ moves into the heme plane, triggering conformational changes that propagate to
other subunits [CORRECT]
Rationale: When O₂ binds, the Fe²⁺ atom moves into the plane of the porphyrin ring,
pulling the F-helix and proximal histidine with it; this movement triggers the breaking of
salt bridges and the T→R quaternary transition that increases affinity in remaining
subunits.
Correct Answer: B
Q5. A researcher measures oxygen binding curves for purified myoglobin and adult
hemoglobin at pH 7.4 in the presence of physiological 2,3-BPG. Which of the following
correctly describes the expected binding curves and P₅₀ values?
A. Both proteins show hyperbolic curves with P₅₀ values near 26 torr
B. Myoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; hemoglobin shows a
sigmoidal curve with P₅₀ ~26 torr
C. Both proteins show sigmoidal curves, but myoglobin has a lower P₅₀ than
hemoglobin
D. Hemoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; myoglobin shows a
sigmoidal curve with P₅₀ ~26 torr
, B. Myoglobin shows a hyperbolic curve with P₅₀ ~2-3 torr; hemoglobin shows a
sigmoidal curve with P₅₀ ~26 torr [CORRECT]
Rationale: Myoglobin is monomeric and exhibits non-cooperative binding with a
hyperbolic curve and high affinity (low P₅₀ ~2-3 torr), whereas hemoglobin's tetrameric
structure produces cooperative binding with a sigmoidal curve and lower affinity (P₅₀
~26 torr) under physiological conditions.
Correct Answer: B
Q6. A newborn is found to have a hemoglobin variant with higher oxygen affinity than
maternal hemoglobin. Electrophoretic analysis reveals the presence of γ-subunits
containing serine at position 143 instead of histidine. This hemoglobin variant is:
A. Hemoglobin S (sickle cell hemoglobin)
B. Hemoglobin A₂ (minor adult hemoglobin)
C. Hemoglobin F (fetal hemoglobin)
D. Hemoglobin A (adult hemoglobin)
C. Hemoglobin F (fetal hemoglobin) [CORRECT]
Rationale: Hemoglobin F (α₂γ₂) is the major fetal hemoglobin; the γ-subunit has serine at
position 143 (instead of histidine in the β-chain), which reduces positive charge in the
central cavity and weakens 2,3-BPG binding, resulting in higher oxygen affinity
(left-shifted curve) that facilitates placental oxygen transfer.
Correct Answer: C
Q7. Adult hemoglobin (HbA) exhibits a specific quaternary structure essential for
cooperative oxygen binding. Which subunit composition and arrangement correctly
describes HbA?
