Multiple Choice
Which process occurs after glycolysis but before the citric acid cycle in cellular respiration?
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Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Pyruvate Oxidation
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How many carbon atoms from one molecule of pyruvate enter the citric acid cycle as part of acetyl-CoA?
A
1
B
2
C
3
D
0
Verified step by step guidance1
Understand the structure of pyruvate: Pyruvate is a 3-carbon molecule (C3H4O3) produced during glycolysis.
Recall the conversion of pyruvate to acetyl-CoA: Pyruvate undergoes oxidative decarboxylation in the mitochondria, catalyzed by the pyruvate dehydrogenase complex. During this process, one carbon atom is released as CO2, leaving a 2-carbon acetyl group.
Recognize the role of acetyl-CoA in the citric acid cycle: The 2-carbon acetyl group from acetyl-CoA combines with a 4-carbon oxaloacetate to form citrate, initiating the citric acid cycle.
Count the carbon atoms entering the cycle: Since the acetyl group contains 2 carbon atoms, these are the ones entering the citric acid cycle as part of acetyl-CoA.
Verify the answer: The number of carbon atoms from one molecule of pyruvate entering the citric acid cycle as part of acetyl-CoA is 2.
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