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BB 451
Citric acid cycle
| Question | Answer |
|---|---|
| Step 1 CAC | Citrate synthase, oxalcetate (OAA) and acetyl CoA join by aldol condensation at OAA C2 (carbonyl group); subsequent cleavage of citryl CoA thioester bond drives reaction. citrate synthase reaction example of ordered substrate binding |
| Step 2 CAC | aconitase isomerizes citrate to isocitrate, the C-3 moves to C-2 position |
| Step 3 CAC | isocitrate DH oxidatively decarboxylates isocitrate. two electrons removed to form NADH+ and H+, caboxyl leaves as CO2 |
| step 4 CAC | a-ketoglutarate DH oxidatively decarboxylates a-KG. NADH+ and H+ is produced and a 4-C succinyl group is generated, reaction scheme is identical to pyruvate DH |
| step 5 CAC | succinyl CoA synthetase produces succinate and GTP. a substrate level phosphorylation is coupled to cleavage if succinyl-CoA thioester bond. involves a phosphohistidine intermediate |
| step 6 CAC | succinate is oxydized to fumarate by succinate dehydrogenase. electrons captured by FAD rather than NAD. enzyme is anchored to matrix face of inner mitochondrial membrane. part of electron transport system |
| Step 7 CAC | Fumarase catalyzes the stereospecific hydration of the C2 and C3 double bond of Fumarate formung L-Malate |
| Step 8 CAC | Malate DH oxidizes malate. NADH + H+ is produced and oxaloacetate is regenerated. energetically unfavorable under standard conditions, but occurs in vivo because of exergonic upstream and downstream rxns |
| symmetric molecules acted on asymmetrically | citrate, aconitase moves OH specifically to C2, fumarate, fumarase adds water such that only L-malate is formed |
Created by:
adam87
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