Unit 4 Module 4.docx - Module 4 Unit 4.1 u2013 Transition...

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Module 4: Unit 4.1 – Transition Reaction and Krebs Cycle REVIEW from previous module Let us begin this unit by reviewing the processes in the two pathways: Cellular respiration Fermentation We studied glycolysis and fermentation. Now, we will study the transition reaction and the Krebs/citric acid cycle. Transition Reaction The transition reaction converts the two molecules of the 3-carbon pyruvic acid (also called pyruvate) from glycolysis into two molecules of the two-carbon molecule acetyl Coenzyme A. (acetyl- CoA) The transition reaction is also called oxidative decarboxylation. Oxidative means loss of electron(s); LEO. Decarboxylation is any chemical reaction in which a carboxyl group -COOH is split off from a compound as carbon dioxide CO 2 . The transition reaction takes place in the matrix of each mitochondrion. It is the beginning of aerobic respiration. Transition reaction will take place as long as there is sufficient amount of oxygen available in the mitochondria. If there is not enough oxygen, then the fermentation pathway will begin. The transition reaction is: the oxidation of pyruvic acid (pyruvate) to acetyl-CoA.

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