CHEM 210 Module 6 Exam ()
Biochemistry | Geneva College | Portage Learning
50 Multiple-Choice Questions | Comprehensive Rationales | Verified Answers
Section 1: Protein Function and Hemoglobin (Oxygen Binding,
Cooperativity, and Allosteric Regulation)
Q1: Hemoglobin is classified as a quaternary protein because it:
A. Consists of a single polypeptide chain with multiple domains
B. Contains four polypeptide subunits (two alpha and two beta chains) that associate
noncovalently **[CORRECT]**
C. Is composed of repeating disaccharide units linked by glycosidic bonds
D. Requires a lipid bilayer environment for proper folding and function
Correct Answer: B
Rationale: Hemoglobin is the classic example of a quaternary protein structure, consisting of two alpha and two beta
subunits held together by noncovalent interactions (hydrogen bonds, ionic interactions, and hydrophobic effects). Each
subunit contains its own heme group capable of binding one oxygen molecule. Option A describes tertiary structure,
option C describes a polysaccharide, and option D describes an integral membrane protein, none of which apply to
hemoglobin.
Q2: What is the primary role of the heme group within each hemoglobin subunit?
A. To provide structural stability through hydrophobic interactions between subunits
B. To bind iron (Fe2+) that serves as the oxygen-binding site **[CORRECT]**
C. To catalyze the conversion of carbon dioxide to bicarbonate in the bloodstream
D. To regulate allosteric transitions between the T and R states through competitive binding
Correct Answer: B
Rationale: The heme group contains an iron atom in the ferrous state (Fe2+) at its center, which is the direct binding site
for molecular oxygen. The iron is coordinated to four nitrogen atoms of the protoporphyrin IX ring and one nitrogen
from a proximal histidine residue of the globin chain. Option A describes the role of hydrophobic amino acid side
chains at the subunit interface, option C describes carbonic anhydrase function, and option D describes the role of
heterotropic effectors such as 2,3-BPG.
Q3: Positive cooperativity in hemoglobin means that:
A. The binding of oxygen to one subunit decreases the affinity of the remaining subunits for
oxygen
B. Each subunit binds oxygen independently with no influence on neighboring subunits
C. The binding of the first oxygen molecule increases the affinity of the remaining subunits
for subsequent oxygen molecules **[CORRECT]**
D. Hemoglobin releases oxygen more readily at higher oxygen partial pressures in the lungs
Correct Answer: C
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 1
,Rationale: Positive cooperativity is the hallmark of hemoglobin function: when one subunit binds oxygen, it induces a
conformational change from the tense (T) state to the relaxed (R) state that propagates to the remaining subunits,
increasing their oxygen affinity. This produces the characteristic sigmoidal oxygen dissociation curve. Option A
describes negative cooperativity, option B describes non-cooperative binding (as seen with myoglobin), and option D
incorrectly reverses the physiological direction of oxygen loading versus unloading.
Q4: The oxygen dissociation curve for hemoglobin is sigmoidal rather than hyperbolic because:
A. Hemoglobin has a single binding site with variable affinity depending on pH
B. Cooperative binding among the four subunits causes the curve to exhibit a steep
transition phase **[CORRECT]**
C. Myoglobin competes with hemoglobin for oxygen, creating the S-shaped curve
D. The heme iron alternates between Fe2+ and Fe3+ during oxygen binding, producing the
sigmoidal shape
Correct Answer: B
Rationale: The sigmoidal shape arises directly from cooperative interactions between hemoglobin subunits. At low
oxygen partial pressures, hemoglobin is predominantly in the low-affinity T state; as oxygen binds, the protein shifts to
the high-affinity R state, creating the steep portion of the curve where small changes in oxygen pressure produce large
changes in saturation. A hyperbolic curve (as seen with myoglobin) reflects non-cooperative, single-site binding. The
heme iron remains Fe2+ during normal oxygen binding and does not oscillate between oxidation states.
Q5: A patient presents with metabolic acidosis (pH 7.30). How will this affect hemoglobin oxygen
binding?
A. Hemoglobin affinity for oxygen will increase, shifting the curve to the left
B. Hemoglobin affinity for oxygen will decrease, shifting the curve to the right and
promoting oxygen release to tissues **[CORRECT]**
C. There will be no effect on hemoglobin oxygen binding because pH only affects enzyme activity
D. Hemoglobin will release all bound oxygen immediately due to irreversible denaturation at low
pH
Correct Answer: B
Rationale: This is the Bohr effect: decreased pH (increased hydrogen ion concentration) stabilizes the T state of
hemoglobin by promoting protonation of specific amino acid residues, which form additional salt bridges that favor
deoxyhemoglobin. The rightward shift of the oxygen dissociation curve means that at any given oxygen partial
pressure, hemoglobin holds less oxygen. This is physiologically advantageous because metabolically active tissues
produce both CO2 and H+, ensuring that oxygen is preferentially released where it is most needed. Option A describes
the opposite (Haldane-like) effect, option C is incorrect because pH directly affects hemoglobin allosteric behavior, and
option D is incorrect because the Bohr effect is fully reversible.
Q6: 2,3-Bisphosphoglycerate (2,3-BPG) binds preferentially to deoxyhemoglobin and:
A. Increases hemoglobin oxygen affinity by stabilizing the R state conformation
B. Decreases hemoglobin oxygen affinity by stabilizing the T state, facilitating oxygen
unloading to tissues **[CORRECT]**
C. Competes directly with oxygen for binding to the heme iron atom
D. Causes irreversible covalent modification of the beta chain histidine residues
Correct Answer: B
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 2
, Rationale: 2,3-BPG is a negatively charged molecule that binds in the central cavity of deoxyhemoglobin (the T state),
forming salt bridges with positively charged residues on the beta chains (His2, Lys82, and His143). This stabilizes the T
state and lowers oxygen affinity, shifting the oxygen dissociation curve to the right. In the R state, the central cavity
narrows and 2,3-BPG is expelled. 2,3-BPG does not compete with oxygen for the heme binding site (it binds at an
allosteric site in the central cavity), and its binding is noncovalent and fully reversible.
Q7: Fetal hemoglobin (HbF) has a higher oxygen affinity than adult hemoglobin (HbA) because:
A. HbF contains two additional heme groups that increase total oxygen-binding capacity
B. HbF has a lower binding affinity for 2,3-BPG, reducing the rightward shift and
maintaining higher oxygen affinity **[CORRECT]**
C. HbF does not exhibit cooperative binding and instead follows hyperbolic kinetics like
myoglobin
D. The gamma chains of HbF bind oxygen with negative cooperativity, preventing oxygen release
in fetal tissues
Correct Answer: B
Rationale: Fetal hemoglobin (HbF) is composed of two alpha chains and two gamma chains (instead of beta chains).
The gamma chains have a serine residue at position 143 instead of histidine, which eliminates a critical positive charge
needed for 2,3-BPG binding. Since 2,3-BPG binds less tightly to HbF, the rightward-shifting effect is diminished, and
HbF maintains a higher oxygen affinity than HbA at any given oxygen partial pressure. This difference allows
efficient oxygen transfer from maternal blood (lower affinity HbA) to fetal blood (higher affinity HbF) across the
placenta. HbF still exhibits cooperative binding (sigmoidal curve) and has the same number of heme groups as HbA.
Q8: During intense exercise, skeletal muscle produces large amounts of CO2 and H+. Which combined
effect optimizes oxygen delivery to the working muscle?
A. Increased pH and elevated 2,3-BPG levels shift the curve to the left, maximizing oxygen uptake
B. The Bohr effect (decreased pH and increased CO2) shifts the oxygen dissociation curve to
the right, promoting oxygen unloading **[CORRECT]**
C. Carbon dioxide directly competes with oxygen at the heme binding site, displacing oxygen
molecules
D. Elevated temperature decreases hemoglobin cooperativity, converting the sigmoidal curve to
hyperbolic
Correct Answer: B
Rationale: During intense exercise, active muscles generate CO2 and metabolic acids (lactic acid), which lower local
pH. Both the increased CO2 and decreased H+ (low pH) stabilize the T state of hemoglobin through the Bohr effect.
This rightward shift of the oxygen dissociation curve ensures that hemoglobin releases oxygen more readily precisely
where it is needed most. Additionally, increased temperature in active muscle further shifts the curve to the right. CO2
does not directly compete with oxygen at the heme site; rather, it exerts its effect through pH changes and carbamate
formation on the N-termini of globin chains.
Q9: Hemoglobin is described as an allosteric protein. Which of the following best defines allostery in the
context of hemoglobin function?
A. The binding of a ligand (oxygen) at one site affects the protein conformation and binding
affinity at distant sites on the same molecule **[CORRECT]**
B. The irreversible covalent attachment of a regulatory molecule that permanently activates or
inhibits the protein
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 3
Biochemistry | Geneva College | Portage Learning
50 Multiple-Choice Questions | Comprehensive Rationales | Verified Answers
Section 1: Protein Function and Hemoglobin (Oxygen Binding,
Cooperativity, and Allosteric Regulation)
Q1: Hemoglobin is classified as a quaternary protein because it:
A. Consists of a single polypeptide chain with multiple domains
B. Contains four polypeptide subunits (two alpha and two beta chains) that associate
noncovalently **[CORRECT]**
C. Is composed of repeating disaccharide units linked by glycosidic bonds
D. Requires a lipid bilayer environment for proper folding and function
Correct Answer: B
Rationale: Hemoglobin is the classic example of a quaternary protein structure, consisting of two alpha and two beta
subunits held together by noncovalent interactions (hydrogen bonds, ionic interactions, and hydrophobic effects). Each
subunit contains its own heme group capable of binding one oxygen molecule. Option A describes tertiary structure,
option C describes a polysaccharide, and option D describes an integral membrane protein, none of which apply to
hemoglobin.
Q2: What is the primary role of the heme group within each hemoglobin subunit?
A. To provide structural stability through hydrophobic interactions between subunits
B. To bind iron (Fe2+) that serves as the oxygen-binding site **[CORRECT]**
C. To catalyze the conversion of carbon dioxide to bicarbonate in the bloodstream
D. To regulate allosteric transitions between the T and R states through competitive binding
Correct Answer: B
Rationale: The heme group contains an iron atom in the ferrous state (Fe2+) at its center, which is the direct binding site
for molecular oxygen. The iron is coordinated to four nitrogen atoms of the protoporphyrin IX ring and one nitrogen
from a proximal histidine residue of the globin chain. Option A describes the role of hydrophobic amino acid side
chains at the subunit interface, option C describes carbonic anhydrase function, and option D describes the role of
heterotropic effectors such as 2,3-BPG.
Q3: Positive cooperativity in hemoglobin means that:
A. The binding of oxygen to one subunit decreases the affinity of the remaining subunits for
oxygen
B. Each subunit binds oxygen independently with no influence on neighboring subunits
C. The binding of the first oxygen molecule increases the affinity of the remaining subunits
for subsequent oxygen molecules **[CORRECT]**
D. Hemoglobin releases oxygen more readily at higher oxygen partial pressures in the lungs
Correct Answer: C
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 1
,Rationale: Positive cooperativity is the hallmark of hemoglobin function: when one subunit binds oxygen, it induces a
conformational change from the tense (T) state to the relaxed (R) state that propagates to the remaining subunits,
increasing their oxygen affinity. This produces the characteristic sigmoidal oxygen dissociation curve. Option A
describes negative cooperativity, option B describes non-cooperative binding (as seen with myoglobin), and option D
incorrectly reverses the physiological direction of oxygen loading versus unloading.
Q4: The oxygen dissociation curve for hemoglobin is sigmoidal rather than hyperbolic because:
A. Hemoglobin has a single binding site with variable affinity depending on pH
B. Cooperative binding among the four subunits causes the curve to exhibit a steep
transition phase **[CORRECT]**
C. Myoglobin competes with hemoglobin for oxygen, creating the S-shaped curve
D. The heme iron alternates between Fe2+ and Fe3+ during oxygen binding, producing the
sigmoidal shape
Correct Answer: B
Rationale: The sigmoidal shape arises directly from cooperative interactions between hemoglobin subunits. At low
oxygen partial pressures, hemoglobin is predominantly in the low-affinity T state; as oxygen binds, the protein shifts to
the high-affinity R state, creating the steep portion of the curve where small changes in oxygen pressure produce large
changes in saturation. A hyperbolic curve (as seen with myoglobin) reflects non-cooperative, single-site binding. The
heme iron remains Fe2+ during normal oxygen binding and does not oscillate between oxidation states.
Q5: A patient presents with metabolic acidosis (pH 7.30). How will this affect hemoglobin oxygen
binding?
A. Hemoglobin affinity for oxygen will increase, shifting the curve to the left
B. Hemoglobin affinity for oxygen will decrease, shifting the curve to the right and
promoting oxygen release to tissues **[CORRECT]**
C. There will be no effect on hemoglobin oxygen binding because pH only affects enzyme activity
D. Hemoglobin will release all bound oxygen immediately due to irreversible denaturation at low
pH
Correct Answer: B
Rationale: This is the Bohr effect: decreased pH (increased hydrogen ion concentration) stabilizes the T state of
hemoglobin by promoting protonation of specific amino acid residues, which form additional salt bridges that favor
deoxyhemoglobin. The rightward shift of the oxygen dissociation curve means that at any given oxygen partial
pressure, hemoglobin holds less oxygen. This is physiologically advantageous because metabolically active tissues
produce both CO2 and H+, ensuring that oxygen is preferentially released where it is most needed. Option A describes
the opposite (Haldane-like) effect, option C is incorrect because pH directly affects hemoglobin allosteric behavior, and
option D is incorrect because the Bohr effect is fully reversible.
Q6: 2,3-Bisphosphoglycerate (2,3-BPG) binds preferentially to deoxyhemoglobin and:
A. Increases hemoglobin oxygen affinity by stabilizing the R state conformation
B. Decreases hemoglobin oxygen affinity by stabilizing the T state, facilitating oxygen
unloading to tissues **[CORRECT]**
C. Competes directly with oxygen for binding to the heme iron atom
D. Causes irreversible covalent modification of the beta chain histidine residues
Correct Answer: B
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 2
, Rationale: 2,3-BPG is a negatively charged molecule that binds in the central cavity of deoxyhemoglobin (the T state),
forming salt bridges with positively charged residues on the beta chains (His2, Lys82, and His143). This stabilizes the T
state and lowers oxygen affinity, shifting the oxygen dissociation curve to the right. In the R state, the central cavity
narrows and 2,3-BPG is expelled. 2,3-BPG does not compete with oxygen for the heme binding site (it binds at an
allosteric site in the central cavity), and its binding is noncovalent and fully reversible.
Q7: Fetal hemoglobin (HbF) has a higher oxygen affinity than adult hemoglobin (HbA) because:
A. HbF contains two additional heme groups that increase total oxygen-binding capacity
B. HbF has a lower binding affinity for 2,3-BPG, reducing the rightward shift and
maintaining higher oxygen affinity **[CORRECT]**
C. HbF does not exhibit cooperative binding and instead follows hyperbolic kinetics like
myoglobin
D. The gamma chains of HbF bind oxygen with negative cooperativity, preventing oxygen release
in fetal tissues
Correct Answer: B
Rationale: Fetal hemoglobin (HbF) is composed of two alpha chains and two gamma chains (instead of beta chains).
The gamma chains have a serine residue at position 143 instead of histidine, which eliminates a critical positive charge
needed for 2,3-BPG binding. Since 2,3-BPG binds less tightly to HbF, the rightward-shifting effect is diminished, and
HbF maintains a higher oxygen affinity than HbA at any given oxygen partial pressure. This difference allows
efficient oxygen transfer from maternal blood (lower affinity HbA) to fetal blood (higher affinity HbF) across the
placenta. HbF still exhibits cooperative binding (sigmoidal curve) and has the same number of heme groups as HbA.
Q8: During intense exercise, skeletal muscle produces large amounts of CO2 and H+. Which combined
effect optimizes oxygen delivery to the working muscle?
A. Increased pH and elevated 2,3-BPG levels shift the curve to the left, maximizing oxygen uptake
B. The Bohr effect (decreased pH and increased CO2) shifts the oxygen dissociation curve to
the right, promoting oxygen unloading **[CORRECT]**
C. Carbon dioxide directly competes with oxygen at the heme binding site, displacing oxygen
molecules
D. Elevated temperature decreases hemoglobin cooperativity, converting the sigmoidal curve to
hyperbolic
Correct Answer: B
Rationale: During intense exercise, active muscles generate CO2 and metabolic acids (lactic acid), which lower local
pH. Both the increased CO2 and decreased H+ (low pH) stabilize the T state of hemoglobin through the Bohr effect.
This rightward shift of the oxygen dissociation curve ensures that hemoglobin releases oxygen more readily precisely
where it is needed most. Additionally, increased temperature in active muscle further shifts the curve to the right. CO2
does not directly compete with oxygen at the heme site; rather, it exerts its effect through pH changes and carbamate
formation on the N-termini of globin chains.
Q9: Hemoglobin is described as an allosteric protein. Which of the following best defines allostery in the
context of hemoglobin function?
A. The binding of a ligand (oxygen) at one site affects the protein conformation and binding
affinity at distant sites on the same molecule **[CORRECT]**
B. The irreversible covalent attachment of a regulatory molecule that permanently activates or
inhibits the protein
CHEM 210 Module 6 Exam | Portage Learning / Geneva College | Page 3
