BIOL 271 MODULE 4 EXAM QUESTIONS
AND ANSWERS
1. Which enzyme acts as the rate-limiting step of glycolysis and is allosterically inhibited by
high levels of ATP and citrate?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1)
C. Pyruvate Kinase
D. Glyceraldehyde-3-phosphate dehydrogenase
Answer: B
Conceptual Explanation: PFK-1 is the primary regulatory enzyme in glycolysis, controlled
by energy status signals like ATP and Citrate.
2. In the Malate-Aspartate shuttle, which molecule is transported into the mitochondrial
matrix to carry reducing equivalents?
A. NADH
B. Oxaloacetate
C. Aspartate
D. Malate
,Answer: D
Conceptual Explanation: Malate carries electrons across the inner mitochondrial
membrane where it is re-oxidized to NADH inside the matrix.
3. What is the specific role of the Oxygen-Evolving Complex (OEC) in Photosystem II?
A. To reduce NADP+ to NADPH
B. To transfer electrons from plastocyanin to P700
C. To fix atmospheric CO2 into RuBP
D. To oxidize water and release protons and oxygen
Answer: D
Conceptual Explanation: The OEC splits water molecules to provide electrons for the
electron transport chain, releasing O2 as a byproduct.
4. During DNA replication, which subunit of DNA Polymerase III is responsible for the 3’ to 5’
exonuclease proofreading activity?
A. Alpha subunit
B. Epsilon subunit
C. Beta clamp
D. Theta subunit
Answer: B
, Conceptual Explanation: The epsilon subunit provides the essential proofreading
function to maintain high fidelity during replication.
5. Which mechanism characterizes the ‘Binding Change Mechanism’ of ATP synthase?
A. Direct phosphorylation of ADP by a proton flux
B. Rotation of the gamma subunit changing the conformation of beta subunits
C. Active transport of ATP across the membrane via a symporter
D. Coupling of ATP hydrolysis to the movement of flagella
Answer: B
Conceptual Explanation: The rotation of the central gamma subunit induces
conformational changes (Open, Loose, Tight) in the catalytic beta subunits to synthesize
ATP.
6. In C4 plants, where does the Calvin Cycle primarily take place to minimize
photorespiration?
A. Bundle sheath cells
B. Stomata
C. Mesophyll cells
D. Epidermal cells
Answer: A
AND ANSWERS
1. Which enzyme acts as the rate-limiting step of glycolysis and is allosterically inhibited by
high levels of ATP and citrate?
A. Hexokinase
B. Phosphofructokinase-1 (PFK-1)
C. Pyruvate Kinase
D. Glyceraldehyde-3-phosphate dehydrogenase
Answer: B
Conceptual Explanation: PFK-1 is the primary regulatory enzyme in glycolysis, controlled
by energy status signals like ATP and Citrate.
2. In the Malate-Aspartate shuttle, which molecule is transported into the mitochondrial
matrix to carry reducing equivalents?
A. NADH
B. Oxaloacetate
C. Aspartate
D. Malate
,Answer: D
Conceptual Explanation: Malate carries electrons across the inner mitochondrial
membrane where it is re-oxidized to NADH inside the matrix.
3. What is the specific role of the Oxygen-Evolving Complex (OEC) in Photosystem II?
A. To reduce NADP+ to NADPH
B. To transfer electrons from plastocyanin to P700
C. To fix atmospheric CO2 into RuBP
D. To oxidize water and release protons and oxygen
Answer: D
Conceptual Explanation: The OEC splits water molecules to provide electrons for the
electron transport chain, releasing O2 as a byproduct.
4. During DNA replication, which subunit of DNA Polymerase III is responsible for the 3’ to 5’
exonuclease proofreading activity?
A. Alpha subunit
B. Epsilon subunit
C. Beta clamp
D. Theta subunit
Answer: B
, Conceptual Explanation: The epsilon subunit provides the essential proofreading
function to maintain high fidelity during replication.
5. Which mechanism characterizes the ‘Binding Change Mechanism’ of ATP synthase?
A. Direct phosphorylation of ADP by a proton flux
B. Rotation of the gamma subunit changing the conformation of beta subunits
C. Active transport of ATP across the membrane via a symporter
D. Coupling of ATP hydrolysis to the movement of flagella
Answer: B
Conceptual Explanation: The rotation of the central gamma subunit induces
conformational changes (Open, Loose, Tight) in the catalytic beta subunits to synthesize
ATP.
6. In C4 plants, where does the Calvin Cycle primarily take place to minimize
photorespiration?
A. Bundle sheath cells
B. Stomata
C. Mesophyll cells
D. Epidermal cells
Answer: A
