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USMLE
New FA Biochem 5
| Question | Answer |
|---|---|
| What are the net reactants and products in glycolysis. | Reactants: 1. Glucose 2. 2 Phosphates 3. 2 ADP 4. 2 NAD Products: 1. 2 Pyruvate 2. 2 ATP 3. 2 NADH 4. 2 H+ 5. 2 H20 |
| What are the rate limiting steps of glycolysis? | 1. Hexokinase (Glucose to Glucose-6-P) 2. *Phosphofructokinase-1 (Fructose-6-P to Fructose-1,6-BP) 3. Pyruvate kinase (Phosphoenolpyruvate to Pyruvate)4. Pyruvate dehydrogenase (Pyruvate to Acetyl-CoA) |
| Phosphofructokinase-1: What does it do, and what stimulates and inhibits it? | PFK-1 1-phosphorylates fructose-6-phosphate to produce Fructose-1,6-BP. Inhibited by: 1. ATP (plenty of me) 2. Citrate (my cycle's going well) Stimulated by: 1. AMP (more ATP please) 2. Fructose-2,6-BP (making me means there's tons of glucose already) |
| Pyruvate kinase: What does it do, and what stimulates and inhibits it? | Pyruvate kinase converts phosphoenolpyruvate to pyruvate, producing 2 ATP. Inhibited by: 1. ATP (plenty of me) 2. Alanine (I came from pyruvate, plenty of me.)Stimulated by: 1. Fructose-1,6-BP(I heard we needed more ATP, get the line moving!) |
| Pyruvate dehydrogenase: What does it do, and what stimulates and inhibits it? | Pyruvate dehydrogenase converts pyruvate to acetyl-coA, producing NADH & CO2. Stimulated by: excess pyruvate? Inhibited by: 1. NADH (plenty. Besides, you produce NADH, soon there'll be even more of me) 3. Acetyl-CoA (Enough of me, save your pyrvuate.) |
| What disease state is glycolytic enzyme deficiency generally associated with? | Hemolytic anemia |
| What is the mechanism of hemolytic anemia in someone with glycolytic enzyme deficiency? | 1. Lack of glycolysis leads to lack of ATP in RBCs. 2. Lack of ATP leads to inactivity of Na, K-ATPase pump. 3. Lack of the pump leads to sodium influx. 4. Water follows sodium into the cell. 5. The cell swells and bursts. |
| What are the two most common glycolytic enzyme deficiencies? | Pyruvate kinase (95% of cases) followed by glucose phosphate isomerase (4% of cases) |
| What are the 5 cofactors necessary for pyrvuate dehydrogenase? | Lipoic acid plus the first four B vitamins in their active forms: 1. B1: TPP 2. B2: FAD 3. B3: NAD 4. B5: CoA |
| What are the 5 cofactors necessary for alpha-ketoglutarate dehydrogenase? | Lipoic acid plus the first four B vitamins in their active forms: 1. B1: TPP 2. B2: FAD 3. B3: NAD 4. B5: CoA |
| What are the net reactants and products in the reaction that Pyruvate Dehydrogenase catalyzes? | Reactants: 1. Pyruvate 2. CoA 3. NAD Products: 1. Acetyl CoA 2. CO2 3. NADH |
| What activates and what inhibits pyruvate dehydrogenase? | Activated by exercise, which stimulates: 1. Increased NAD/NADH ratio (need more NADH) 2. Increased ADP (need more ATP) 3. Ca2+ (I tell PDH in mito we need more ATP) Inhibited by: 1. NADH (plenty of me) 2. ATP (ditto) 3. Acetyl CoA (ditto) |
| Lipoamide or lipoate: Which carries aldehydes? | Lipoamide |
| Lipoamide or lipoate: Which is a cofactor for pyruvate dehydrogenase? | Lipoate (Lipoic acid) |
| What toxin inhibits lipoic acid? | Arsenic |
| What is the presentation of arsenic toxicity? | 1. Vomiting 2. Rice water stools 3. Garlic breath |
| Pyruvate dehydrogenase deficiency: Mechanism | Backup of pyruvate and alanine leads to lactic acidosis. |
| Pyruvate dehydrogenase deficiency: Congenital or Acquired | Both. Acquired cases happen in cases of B1 deficiency (such as in alcoholics.) |
| Pyruvate dehydrogenase deficiency: Presentation | Lactic acidosis and neurologic defects |
| Pyruvate dehydrogenase deficiency: Treatment | Increased intake of ketogenic nutrients (such as high fat content or increased lysine and leucine) |
| What are the miscellaneous fates of pyruvate, and what are the end products used for? | 1. Alanine: Carries amino groups to the liver from muscle 2. Oxaloacetate: Replenishes TCA cycle or is used gluconeogenesis 3. Acetyl-CoA: Used in TCA cycle 4. Lactate: No good use |
| Which tissues and organs primarily convert pyruvate into lactate? | 1. RBCs and WBCs 2. Lens and cornea 3. Renal medulla 4. Testes |
| What enzymes and cofactors are used in conversion of pyruvate to alanine? | Enzyme: Alanine Transaminase (ALT) Cofactors: None |
| What enzymes and cofactors are used in conversion of pyruvate to oxaloacetate? | Enzyme: Pyruvate Carboxylase (contains biotin and magnesium) Cofactors: CO2 and ATP |
| What are the reactants and products in the reaction catalyzed by pyruvate carboxylase? | Reactant: Pyruvate (with CO2 and ATP) Product: Oxaloacetate |
| What are the reactants and products in the reaction catalyzed by lactate dehydrogenase? | This reaction is reversible, so the products can switch with the reactants. Reactants: 1. Pyruvate 2. NADH (rehydrogenates in this direction) 3. H+ Products: 1. Lactate 2. NAD |
| Where do the various pyruvate transformation reactions happen? | Cytosol: 1. ALT (Alanine to/from pyruvate) 2. LDH (Lactate to/from pyruvate) Mitochondria: 1. Pyruvate carboxylase (pyruvate to oxaloacetate) 2. Pyruvate dehydrogenase (pyruvate to acetyl-CoA) |
| Where does the Cori Cycle happen? | In the liver and muscle/RBCs Liver: Pyruvate converts to glucose Muscle/RBCs: Glucose converts to Pyruvate |
| What is the purpose of the Cori cycle? | Transfers excess reducing equivalents from RBCs and the muscle to liver so they can function anaerobically |
| What reaction does citrate synthase catalyze? | Oxaloacetate and acetyl coA combine to yield citrate. |
| What is the order of the citric acid cycle beginning at citrate? | “CAn I Keep Selling Sex For Money, Officer?” 1. Citrate 2. cis-Aconitate 3. Isocitrate 4. alpha-Ketoglutarate 5. Succinyl CoA 6. Succinate 7. Fumarate 8. Malate 9. Oxaloacetate |
| What stimulates and inhibits citrate synthase? | Stimulate: Nothing Inhibit: ATP |
| What stimulates and inhibits isocitrate dehydrogenase? | Stimulate: ADP Inhibit: 1. ATP 2. NADH |
| What stimulates and inhibits alpha-ketoglutarate dehydrogenase? | Stimulate: Nothing Inhibit: 1. ATP 2. NADH 3. Succinyl CoA |
| Which steps in the citric acid cycle produce CO2? | The steps where carbons are lost, the two structures after isocitrate each have one less carbon than the last. 1. Isocitrate to alpha-ketoglutarate 2. alpha-ketoglutarate to succinyl coA |
| Which steps in the citric acid cycle produce reducing equivalents? | The only step that produces FADH2 is the only one that also yields an F product. 1. Isocitrate to alpha ketoglutarate (1 NADH) 2. alpha-ketoglutarate to succinyl coA (1 NADH) 3. Succinate to Fumarate (1 FADH2) 4. Malate to Oxaloacetate (1 NADH) |
| Which steps in the citric acid cycle produce ATP? | None, however 1 GTP is produced from the conversion of Succinyl CoA to Succinate. |
| How much ATP is produced by the citric acid cycle per molecule of acetyl coA? | 12 ATP. 3 NADH x 3 ATP/NADH= 9 ATP 1 FADH2 x 2 ATP/FADH2 = 2 ATP 1 GTP x 1 ATP/GTP = 1 ATP |
| How much ATP is produced by the citric acid cycle per molecule of glucose? | 24 ATP. 1 cycle: 3 ATP/NADH= 9 ATP 1 FADH2 x 2 ATP/FADH2 = 2 ATP 1 GTP x 1 ATP/GTP = 1 ATP The total is 12 ATP per acetyl coA. However, there are 2 acetyl coA molecules produced per glucose molecule. Thus the total is 24. |
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Asclepius
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