Multiple Choice
In the citric acid (Krebs) cycle, which molecule is released as the primary waste product for each turn of the cycle?
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Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Citric Acid Cycle 1
Multiple Choice
In the citric acid (Krebs) cycle, why is it described as a "cycle"?
A
Because the pathway regenerates oxaloacetate at the end, allowing acetyl-CoA to enter again and the sequence of reactions to repeat.
B
Because all reactions occur only in the cytosol and do not require mitochondrial enzymes.
C
Because each turn produces one molecule of glucose from units.
D
Because acetyl-CoA is regenerated at the end of the pathway to drive the next round.
Verified step by step guidance1
Understand the definition of a metabolic cycle: a series of biochemical reactions where the starting molecule is regenerated at the end, allowing the process to repeat continuously.
Identify the key molecule in the citric acid cycle that is regenerated: oxaloacetate is the molecule that combines with acetyl-CoA at the start and is regenerated at the end of the cycle.
Recognize that acetyl-CoA enters the cycle by combining with oxaloacetate to form citrate, initiating the sequence of reactions.
Note that the regeneration of oxaloacetate at the end of the cycle allows the pathway to accept another acetyl-CoA molecule, making the process cyclic.
Conclude that the citric acid cycle is described as a 'cycle' because it regenerates oxaloacetate, enabling continuous processing of acetyl-CoA through repeated turns of the pathway.
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