ReviewLet us begin this unit by reviewing the processes in the two pathways:Cellular respirationFermentationOXYGEN PRESENT - AEROBICCELLULAR RESPIRATIONOXYGEN NOT PRESENT - ANAEROBICFERMENTATIONglycolysisglycolysistransition reactionfermentationCitric Acid / Krebs cycleelectron transport chain (ETC)We studied glycolysis and fermentation. Now, we will study the transition reaction and the Krebs/citricacid cycle.Transition ReactionThe 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.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 acompound as carbon dioxide CO2.The transition reaction takes place in the matrix of each mitochondrion. It is the beginning of aerobicrespiration. Transition reaction will take place as long as there is sufficient amount of oxygen availablein the mitochondria. If there is not enough oxygen, then the fermentation pathway will begin.
