When Acetyl-CoA Containing Radioactively Labeled Carbon Atoms Is Fed to Cells,the

question 40

Multiple Choice

When acetyl-CoA containing radioactively labeled carbon atoms is fed to cells,the CO₂ produced is not initially radioactive.However,molecules of citrate and oxaloacetate are radioactive.Only after some time has passed will radioactive CO₂ released.What is the best explanation for this observation?

• A)Acetyl groups are not metabolized directly into CO₂,but enter a linear metabolic pathway.
• B)Acetyl groups are not metabolized directly into CO₂,but enter a cyclical metabolic pathway.
• C)Acetyl groups first combine with citrate and oxaloacetate before being metabolized into CO₂.
• D)Acetyl groups are metabolized directly into CO₂.

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