The Tricarboxylic Acid Cycle
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15 terms
Terms | Definitions |
|---|---|
 1. What is the role of the TCA cycle | central position in intermediary metabolism - Amphibolic - both catabolic and anabolic - cyclic - Catabolic oxidation of acetyl CoA and anabolic in the fact that its intermediates are used for synthesis of amino acids, heme and glucose. |
| 2. Know the intermediates and enzymes of the TCA cycle and the order in which they are produced or function | Draw it! |
| Citrate synthase | primary step in TCA cycle - irreversible - turns oxaloacetate, Acetyl CoA and water into Citrate and CoASH |
| Aconitase | turns citrate into cis-aconitate into isocitrate irreversibly |
| Isocitrate dehydrogenase | important rate limiting step of TCA cycle - isocitrate and NAD become oxalosuccinate and NADH - add an H+ and release a CO2 (spontaneously and irreversibly) to become alpha-ketoglutarate |
| Alpha-ketoglutarate dehydrogenase complex | turns alpha ketoglutarate, NAD+ and CoASH into Succinyl CoA, NADH and CO2 (irreversible) |
| Succinyl CoA synthetase (succinate thiokinase) | Turns Succinyl CoA, Pi and GDP into Succinate, GTP and CoASH reversibly |
| Succinate Dehydrogenase | turns Succinate and FAD into fumarate and FADH2 |
| Fumarase | turns fumarate and H2O into Malate |
| Malate Dehydrogenase | turns Malate and NAD into oxaloacetate and NADH |
| 3. What does fluorocitrate inhibit? | inhibits aconitase - fluorine binds to Fe2+ in active site of enzyme - fluoroacetate is in some toxic plants - can be activated to fluoroacetyl-CoA and converted to fluorocitrate by citrate synthase |
| Malonate | is a structural analogue of succinate but acts as a competitive inhibitor of succinate dehydrogenase - binds to the enzyme but it cannot react |
| 4. Energetics of the TCA cycle | 3NADH (7.5) + 1 FADH2 (1.5) + GTP (1) = 10 ATP/ acetyl CoA molecule that is oxidized - completely dependent on oxygen |
| 5. Why is aerobic metabolism of glucose using the TCA cycle more efficient than anaerobic glycolysis | anaerobic = 2 ATP, aerobic = 34 ATP (using the malate aspartate shuttle, less if you take into consideration transporting ADP, ATP and pyruvate across the inner mitochondrial membrane |
| 6. Where are the 4 major control sites for the TCA cycle | 3 irreversible steps - 1. Citrate synthase reaction by citrate (-) and oxaloacetate (+), competitively binding for citrate synthase - pyruvate can become oxaloacetate to push the reaction forward. 2. Isocitrate Dehydrogenase - by ADP (+) and ATP (-), NADH (-), Ca+ ions (+) - provide immediate stimulus for muscle contraction - increase need of ATP 3. Alpha Ketoglutarate dehydrogenase - Succinyl CoA (-), NADH (-), and Ca+ (+). 4. Oxygen availability - NAD is limited, needs O2 to oxidize NADH - TCA rate is limited because of shortage of NAD+ |
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