Multiple Choice
In eukaryotic cells, where does the Krebs (citric acid) cycle primarily occur?
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Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Citric Acid Cycle 1
Multiple Choice
In human aerobic metabolism, which molecule is the primary waste product ultimately produced from complete oxidation of carbon fuels in the citric acid cycle and oxidative phosphorylation?
A
(glucose)
B
C
D
(carbon dioxide)
Verified step by step guidance1
Step 1: Understand that in human aerobic metabolism, glucose (C\6H\12O\6) undergoes complete oxidation through glycolysis, the citric acid cycle, and oxidative phosphorylation to produce energy.
Step 2: Recognize that during this process, glucose is first broken down into pyruvate (C\3H\4O\3\(\textsuperscript{-}\)), which is then converted into acetyl-CoA (containing acetate, C\2H\3O\2\(\textsuperscript{-}\)) before entering the citric acid cycle.
Step 3: In the citric acid cycle, acetyl groups are fully oxidized, and the carbon atoms from glucose are released as carbon dioxide (CO\2), which is the primary waste product of this metabolic pathway.
Step 4: Recall that oxidative phosphorylation uses the electrons from these oxidation reactions to produce ATP, but the carbon atoms themselves are expelled as CO\2, not retained in other molecules.
Step 5: Therefore, the molecule that represents the primary waste product from the complete oxidation of carbon fuels in aerobic metabolism is carbon dioxide (C\1O\2).
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