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Shortcut used: Identify the tested biochemical principle, track charge/carbon/electrons or pathway direction, use the passage data, and reject choices that contradict cellular location or chemical behavior.
Solve in 3 steps:
- Mark the given values and the exact target.
- Apply the relevant formula, rule, or concept.
- Check the final value against the options.
Common mistake: Do not choose an option before confirming the exact demand of the question.
Question 7
Multiple Choice Question
Question
PASSAGE 3 — MITOCHONDRIAL RESPIRATION
Isolated mitochondria receive succinate as the only respiratory substrate. Oxygen consumption and ATP production are measured. Rotenone, an inhibitor of Complex I, causes little change. Antimycin A, an inhibitor of Complex III, stops oxygen consumption. In a separate trial, an uncoupler carries protons across the inner mitochondrial membrane; oxygen consumption rises, but ATP production falls sharply.
QUESTION 7: Why does rotenone have little effect when succinate is the only substrate?
Explanation
Correct Answer: C
ANSWER
Correct Answer: C
Method / Topic: Biochemistry
The correct answer is C: Electrons from succinate enter through Complex II, bypassing Complex I. Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential.
Why this answer is correct
The correct option matches the required rule and the given information.
Short Explanation
The correct answer is C: Electrons from succinate enter through Complex II, bypassing Complex I. Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential.
Detailed Explanation
Question
PASSAGE 3 — MITOCHONDRIAL RESPIRATION
Isolated mitochondria receive succinate as the only respiratory substrate. Oxygen consumption and ATP production are measured. Rotenone, an inhibitor of Complex I, causes little change. Antimycin A, an inhibitor of Complex III, stops oxygen consumption. In a separate trial, an uncoupler carries protons across the inner mitochondrial membrane; oxygen consumption rises, but ATP production falls sharply.
QUESTION 7: Why does rotenone have little effect when succinate is the only substrate?
ANSWER
Correct Answer: C
Method / Topic: Biochemistry
Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential. To solve this kind of MCAT biochemistry
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Question 7
Learn + Solve: Shortcut, Trap & Fast Route Click to view shortcut, steps, and common mistake
Learn + solve
Shortcut used, common trap, and the fastest solving route
Shortcut used: Identify the tested biochemical principle, track charge/carbon/electrons or pathway direction, use the passage data, and reject choices that contradict cellular location or chemical behavior.
Solve in 3 steps:
- Mark the given values and the exact target.
- Apply the relevant formula, rule, or concept.
- Check the final value against the options.
Common mistake: Do not choose an option before confirming the exact demand of the question.
Question
PASSAGE 3 — MITOCHONDRIAL RESPIRATION Isolated mitochondria receive succinate as the only respiratory substrate. Oxygen consumption and ATP production are measured. Rotenone, an inhibitor of Complex I, causes little change. Antimycin A, an inhibitor of Complex III, stops oxygen consumption. In a separate trial, an uncoupler carries protons across the inner mitochondrial membrane; oxygen consumption rises, but ATP production falls sharply. QUESTION 7: Why does rotenone have little effect when succinate is the only substrate?
Explanation
Correct Answer: C
ANSWER
Correct Answer: C
Method / Topic: Biochemistry
The correct answer is C: Electrons from succinate enter through Complex II, bypassing Complex I. Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential.
Why this answer is correct
The correct option matches the required rule and the given information.
Short Explanation
The correct answer is C: Electrons from succinate enter through Complex II, bypassing Complex I. Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential.
Detailed Explanation
Question
PASSAGE 3 — MITOCHONDRIAL RESPIRATION
Isolated mitochondria receive succinate as the only respiratory substrate. Oxygen consumption and ATP production are measured. Rotenone, an inhibitor of Complex I, causes little change. Antimycin A, an inhibitor of Complex III, stops oxygen consumption. In a separate trial, an uncoupler carries protons across the inner mitochondrial membrane; oxygen consumption rises, but ATP production falls sharply.
QUESTION 7: Why does rotenone have little effect when succinate is the only substrate?
ANSWER
Correct Answer: C
Method / Topic: Biochemistry
Succinate dehydrogenase is Complex II and transfers electrons to ubiquinone without using Complex I. Therefore blocking Complex I with rotenone does not prevent succinate-derived electrons from reaching the downstream chain, although Complex III remains essential. To solve this kind of MCAT biochemistry
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