15 CAC - B iochemis ry E duca ion Department of iochemistry...

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Unformatted text preview: B iochemis ry E duca ion Department of iochemistry & Molecular iology University of New Mexico BIOC 423 Int oducto y Biochemist y Pyruvate Dehydrogenase and Reactions of the Citric Acid Cycle (AKA: CAC, TCA, Krebs Cycle) OBJECTIVES Understand the overall purpose and know the sub-cellular locations of the enzymes of the citric acid cycle. Know the structures of all intermediates in the citric acid cycle. Know the substrates, products and enzymes involved in all reactions that produce or consume ATP, GTP and NADH or FADH 2. Know which type of reaction occurs at each step in the citric acid cycle, e.g. hydration, oxidation, decarboxylation, etc. Know the common intermediate that links the citric acid cycle with glycolysis, protein catabolism and fatty acid oxidation. Understand the importance and enzyme mechanism of pyruvate dehydrogenase OUTLINE Pyruvate Dehydrogenase Pasteur effect A third solution to the NADH problem PDH mechanisms Reactions of the CAC cycle CAC: also known as: Tricarboxylic acid cycle, TCA cycle, Krebs cycle Role of the CAC in metabolism Role of the mitochondria and transport of pyruvate into the mitochondria Know: names, structures, enzymes, cofactors and regulation LECTURE Pyruvate Dehydrogenase In the previous lecture, in order to continue glycolysis, we disposed of pyruvate by either reducing it to lactate or decarboxylating it and reducing the resulting acetaldehyde to ethanol. The key word here is reduce. Both pathways can regenerate the NAD + that is necessary to continue glycolysis. The pathway that is selected is species dependent. Anaereobic yeast use the alcohol dehydrogenase pathway generating ethanol following a decarboxylation of pyruvate to acetaldehyde. Anaerobic muscle and RBC use the lactate dehydrogenase fermentation producing lactate. Pasteur effect: While studying fermentation and alcohol production Pasteur observed that when oxygen was allowed into an anaerobic culture of yeast: 1) the growth rate of the yeast increased dramatically. 2) the increased growth was accompanied by a large drop in glucose consumption (i.e., in the presence of O 2 yeast grew faster on less food). They also did not produce alcohol. These contradictory data could not be explained at the time, however, it is now known that there is a third, aerobic method, for the disposal of NADH that is responsible for the Pasteur effect. This pathway is catalyzed by the enzyme pyruvate dehydrogenase and the Citric Acid Cycle (AKA: CAC, TCA, Krebs Cycle) and requires a totally new anatomic location in the cell. Whereas glycolysis happens in the cytoplasm, the reactions in this lecture take place in matrix of the mitochondria. Answers to the required metabolic questions: Your answers to our Why, Where, When, and What questions of metabolism should have been very obvious for glycolysis. The answers to these questions will change somewhat for the CAC. Why is it important? The answer continues to relate to both harvesting energy is it important?...
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15 CAC - B iochemis ry E duca ion Department of iochemistry...

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