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26 Cards in this Set
- Front
- Back
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enzymes and cofactors involved in pyruvate dehydrogenase complex
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-pyruvate dehydrogenase (E1)
-dihydrolipoyl transacetylase (E2) -dihydrolipoyl dehyrdogenase (E3) -thiamine pyrophosphate -lipoic acid -FAD -coenzyme A -NAD+ |
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4 steps of conversion of pyruvate to acetyl CoA
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1) pyruvate combines with thiamine pyrophosphate and is decarboxylated by E1
2) hydroxyethyl group is oxidized to form acetyl group and is trasnferred to lipoamide 3) acetyl group is transferred to CoA by E2 4) dihydrolipoyl dehydrogenase (E3) oxidizes lipoamide to begin cycle again |
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net reaction of pyruvate dehyrdogenase complex
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pyruvate + CoA + NAD+--->acetyl CoA + CO2 + NADH + H+
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8 enzymes of TCA cycle
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citrate synthase
aconitase isocitrate dehyrdogenase alpha-ketoglutarate dehydrogenase succinyl CoA synthase succinate dehydrogenase fumarase malate dehydrogenase |
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citrate synthase
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-OAA + acetyl CoA --> citryl CoA --> citrate
-involves large conformational change that prescribes the order of addition -OAA binding induces structural change leading to creation of binding site for acetyl CoA |
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citryl CoA
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high energy thioester intermediate that drives the reaction of OAA + acetyl CoA toward citrate
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aconitase
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-citrate --> cis-aconitate --> isocitrate
-consists of dehyrdation then hydration reaction -tertiary hydroxyl group is not properly locate in citrate molecule for next steps, so aconitase moves it |
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isocitrate dehydrogenase
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-isocitrate-->oxalosuccinate-->alpha-ketoglutarate
-the rate of this step is important in determining rate of cycle -generates NADH and CO2 |
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alpha ketoglutarate dehydrogenase
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-alpha-ketoglutarate + NAD+ + CoA --> succinyl CoA + CO2 + NADH
-complex employs cofactors/rxns homologous to pyruvate dehydrogenase complex -alpha-ketoglutarate dehydrogenase (E2) and transsuccinylase (E1) are different but homologous to PDC -dihydrolipoyl dehydrogenase (E3)=identical |
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succinyl CoA synthetase
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-succinyl CoA + Pi + GDP --> succinate + CoA + GTP
-succinyl CoA is a high-energy thioester compound--cleavage of thioester bond is coupled to phosphorylation of GDP -has His in active site |
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succinate dehydrogenase
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-succinate-->fumarate
-includes conversion of FAD to FADH2 and hydration reaction |
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malate dehydrogenase
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-malate-->oxaloacetate
-includes NAD+-->NADH +H+ |
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for each acetyl CoA unit, TCA cycle generates...
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-3 NADH
-1 GTP -1FADH2 |
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1 NADH=approximately ____
1 FADH2=approximately ____ |
2.5 ATP
1.5 ATP |
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overall TCA cycle reaction
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acetyl CoA + 3NAD+ + FAD + GDP + Pi + 2H2O===>2CO2 + 3 NADH + FADH2 + GTP + 2H + CoA
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regulation of pyruvate dehydrogenase complex
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allosterically: acetyl CoA inhibits E2 transacetylase and NADH inhibits E3
-reversible phosophorilation: increasing NADH/NAD+, acetyl CoA/CoA or ATP/ADP ratio promotes phosphorylation of E2 |
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mechanism of key regulator of pyruvate dehydrogenase complex
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-when energy levels are high, kinase phosphorylates PDH (makes it inactive) using ATP
-when energy levels are low, phosphatase dephosphorylates PDH -ADP and pyruvate inhibit PDH kinase, Ca2+ stimulates PDH phosphatase |
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regulation of TCA cycle
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-isocitrate dehydrogenase is allosterically stimulated by ADP (increasing affinity for substrate), NADH and ATP are inhibitory
-alpha-ketoglutarate dehydrogenase is inhibited by succinyl CoA + NADH (its products), also inhibited by ATP |
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citrate can be made into
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fatty acids, sterols
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how is oxaloacetate replenished?
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-pyruvate carboxylase (biotin-dependent) carboxylates pyruvate using CO2 to yield oxaloacetate
-also regenerated by generation of intermediates |
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alpha-ketoglutarate can be made into
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glutamate, other amino acids, purines
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succinyl CoA can be made into
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hemes, porphyrins, chlorophyll
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oxaloacetate can be made into
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aspartate, other amino acids, pyrimidines, purines
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at which steps in the TCA cycle is NADH produced?
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isocitrate-->alpha ketoglutarate
alpha-ketoglutarate-->succinyl CoA malate-->OAA |
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at which step in the TCA cycle is GTP produced?
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succinyl CoA-->succinate
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major regulatory points of TCA cycle
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pyruvate-->acetyl CoA (ATP, acetyl CoA and NADH negatively, ADP and pyruvate positively)
isocitrate--> alpha-keto alpha-keto-->succinyl CoA |
