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Concept 9.3 -- The citric acid cycle completes the energy-yielding oxidation of organic molecules. • Define Acetyl CoA (Upon entering the mitochondrion via active transport, pyruvate is first converted to a compound called acetyl coenzyme A) • Three reactions: the junction between glycolysis and the citric acid cycle, is accomplished by a multienzyme complex that catalyzes three reactions. • The citric acid cycle is also called the tricarboxylic acid cycle or the Krebs cycle The entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme. (Acetyl CoA) (1) Pyruvate′s carboxyl group (—COO − ), which is already fully oxidized and thus has little chemical energy, is removed and given off as a molecule of CO 2 . (This is the first step in which CO 2 is released during respiration.) (2) The remaining two–carbon fragment is oxidized, forming a compound named acetate (the ionized form of acetic acid). An enzyme transfers the extracted electrons to NAD
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