5-423-08CACRegGlyoxStudent

5-423-08CACRegGlyoxStudent - CITRIC ACID CYCLE, REGULATION...

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CITRIC ACID CYCLE, REGULATION OF CAC, GLYOXYLATE CYCLE Objectives Understand the overall reaction of the pyruvate dehydrogenase complex. Where is it located? What coenzymes are integral to this complex? 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 enzymes and cofactors involved in all reactions of the citric acid cycle Know which reactions in the citric acid cycle are regulated, which molecules regulate these reactions, and understand how these regulators integrate the reactions of citric acid cycle with demands for the products of the citric acid cycle. Know which other metabolic pathways are fed by the citric acid cycle. What does anaplerotic mean? Understand the significance of the pyruvate carboxylase reaction. Understand the function and know the sub-cellular locations of the enzymes of the glyoxylate cycle. This cycle is important for what types of organisms? Outline I. Big picture Citric acid cycle = CAC = tricarboxylic acid cycle = TCA cycle = Kreb's cycle A. Overview: Final common pathway for the oxidation of organic molecules. CAC cycle is the central metabolic process. All catabolic pathways feed into it, usually through acetyl-CoA. Also all biosynthetic pathways begin with intermediates from the CAC cycle. In eukaryotes, CAC located in the mitochondria. Pyruvate, the product of glycolysis, enters the mitochondria from the cytosol which is the location of the glycolytic process. Pyruvate is oxidatively decarboxylated to acetyl-CoA and CO2 by the pyruvate dehydrogenase complex, with generation of an NADH B. Brief outline of the cycle itself: 1. Acetyl CoA condenses with a four-C cpd oxaloacetate to form citric acid, a 6-C tricarboxylic acid. 2. The citric acid undergoes oxidative decarboxylation to produce a 5-C cpd
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alpha-ketoglutarate, CO2, and NADH. 3. The 5-C cpd undergoes another oxidative decarboxylation to produce a 4-C cpd, succinate, another CO2, an A(G)TP by substrate level phosphorylation, and another NADH. 4. Succinate is rearranged into oxaloacetate (4-C), generates another NADH, and an FADH2. 5. Overall, two C atoms enter cycle as an acetyl group and exit as CO2 which requires four oxidation steps that generate 3 NADH and 1 FADH2 The electron carriers are regenerated by donating their electrons to the ETS from which 11 ATP are generated - 3 from each NADH and 2 from FADH2. Also have one GTP by substrate-level phosphorylation. NET REACTION Acetyl CoA + 3 NAD+ + FAD + GDP + Pi + 2 HOH ========> 2 CO2 + 3 NADH + FADH2 + GTP + 3 H+ + CoA Notice! No net formation or use of any of the 4,5,6-C intermediates; it is a cycle! The point? To generate ATP, NADH, metabolic intermediates
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5-423-08CACRegGlyoxStudent - CITRIC ACID CYCLE, REGULATION...

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