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60 Cards in this Set
- Front
- Back
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what is the main function of the TCA cycle?
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allows oxidation of metabolic intermediates to CO2 and H20 in a manner that allows the energy released by the oxidation to be captured in NADH, FADH2, and GTP
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main substrate consumed by the TCA cycle?
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Acetyl CoA from Pyruvate
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how many carbons are released as C02 in one full turn of the TCA cycle?
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2
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what does it mean for Citrate to be prochiral?
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enzymes CAN tell the two different sides even though a mirror could not distinguish the two sides of a molecule
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where do the carbons that are released as CO2 come from?
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OAA
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Citrate Synthase
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Acetyl CoA + OAA -> Citrate
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where does cleavage of thiolester bond (high energy) occur?
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Citrate Synthase step
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what enzyme can distinguish the un-equivalent groups of Citrate?
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Aconitase
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Aconitase
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catalyzes DEHYRDATIION of Citrate to Cis-ACONITATE......also REHYDRATES this molecule back to ISOCITRATE
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what is the purpose of Aconitase Dehydrating and then Rehydrating the Citrate molecule?
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move the OH group of Citrate to a position where it can be oxidized to a ketone
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active site of Aconitase
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Iron-Sulfur Center
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Purpose of Iron Sulfur Centers
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help position substrates in the active site
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Isocitrate Dehydrogenase converts Isocitrate to.....?
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alpha-ketoglutarate....(2 steps..first oxidized to ketone)
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First step where NADH is released?
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Isocitrate Dehydrogenase (know because oxidation of alcohol to ketone has occured)
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where is first C02 lost and why?
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Isocitrate step- unstable B- Keto acid
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alpha-ketoglutarate step converts alpha ketoglutarate to ? Same as what other mechanism?
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Succinyl CoA
Pyruvate Dehydrogenase Complex mechanism |
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key differences in alpha ketoglutarate stop and Pyruvate Dehydrogenase Complex reaction?
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different substrate (alpha ketoglutarate)
NOT regulated by phosphorylation |
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cofactors used by Alpha Ketoglutarate Dehydrogenase
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TPP, lipoic acid, FAD
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where is the second high energy thioester bond found?
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Succinyl CoA
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Succinyl CoA Synthetase
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harvest energy of Succinyl CoA as GTP by converting it to Succinate
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where is substrate level phosphorylation in the TCA cycle?
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Succinyl CoA Synthetase
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where is plane of symmetry present and carbons can no longer be tracked?
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Succinate
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can be sure to say that in Succinate, one carboxylate and one methyl came from____?
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Acetyl CoA
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After what molecule are the steps just to get back to OAA?
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After Succinate
Fumarate Malate OAA |
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Succinate Dehydrogenase
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oxidizes Succinate to Fumarate
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what is released as Succinate is oxidized to Fumarate?
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FADH2
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what is the one enzyme that is not free floating in matrix, but it embedded in the Inner Mitochondrial Membrane?
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Succinate Dehydrogenase
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What two enzymes contain Iron Sulfur Centers?
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Aconitase
Succinate Dehydrogenase |
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What happens in Fumarase step
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Water is added to convert fumarate to malate
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which enzyme catalyzes step with an unfavorable equillibrium?
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Malate Dehydrogenase
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where is third NADP released in TCA cycle?
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Malate Dehydrogenase step
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how does Malate Dehydrogenase work even though has unfavorable equillibrium?
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OAA is depleted in TCA cycle so it drives this reaction forward.....In addition, NAD concentrations in the cell are much greater than NADH
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94% of energy is stored in TCA cycle...where is all of the energy stored?
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NADH, FADH2 and GTP
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where are the CO2 producing carbons of the TCA cycle? ones that come off?
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C1 and C4 of OAA
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after how many turns of the TCA cycle will the Carbonyl C of Acetyl CoA be removed?
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2 turns
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what are the key regulators of the TCA cycle?
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NAD/NADH, ATP/ADP, and Succinyl CoA
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What are the three major enzyme sites of regulation in the TCA Cycle
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1) Citrate Synthase
2) Isocitrate Dehydrogenase 3) alpha-Ketoglutarate Dehydrogenase |
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What is Citrate Synthase inhibited by?
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ATP, NADH and Succinyl CoA
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what makes Isocitrate more effective at lower concentrations?
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ADP
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what negatively modulates Isocitrate Dehydrogenase? positively?
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negatively- ATP, NADH
positively- ADP, NAD |
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what negatively modulates alpha Ketoglutarate Dehydrogenae?
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Succinly CoA and NADH (much like Pyruvate Dehydrogenase Complex)
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4 Sources of Acetyl CoA
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1) Pyruvate Dehydrogenase Complex
2) Fatty Acid Oxidation 3) Amino Acids- Isoleucine, Leucine, and Tryptophan |
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Amino Acids that can yield Acetyl CoA
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Leucine, Isoleucine, and Tryptophan
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steps in producing acetyl CoA from ethanol
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ethanol- acetaldehyde- acetic acid- acetyl CoA
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Three enzymes required for the production of acetyl CoA from ethanol?
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1) Alcohol Dehydrogenase
2) Aldehyde Dehydrogenase 3) Acetyl CoA Synthetase |
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what can inhibit gluconeogenesis?
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Ethanol
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How can gluconeogenesis use intermediates from the TCA cycle?
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OAA (actually must be converted to malate by reversal of the malate dehydrogenase reaction or else to aspartate before it can leave the matrix to go to the cytosol)
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How can lipids use intermediates of the TCA cycle?
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Citrate goes out into the cytosol and is converted to Acetyl CoA
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Enzyme that converts Citrate to Acetyl CoA in the cytosol?
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Citrate Lyase
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How can amino acid biosynthesis use intermediates of the TCA cycle?
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OAA ---> Aspartate
a-ketoglutarate---> Glutamate |
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What does the synthesis of porphyrin (heme) require?
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Succinyl CoA
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reactions that REPLENISH the intermediates of the TCA cycle are called?
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ANAPLEROTIC REACTIONS
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The main anaplerotic reaction?
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Pyruvate Carboxylase (Pyruvate--> OAA)
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what does Pyruvate Carboxylase require as a cofactor?
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Biotin
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what activates Pyruvate Carboxylase?
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the accumulation of Acetyl CoA
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If Acetyl CoA accumulates due to the lack of OAA, then ....
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more OAA is formed
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If Acetyl CoA accumulates for another reason besides depletion of OAA....
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OAA is still formed, but it is converted to Malate or Aspartate for GLUCONEOGENESIS
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Two fates of Pyruvate (list enzymes that coincide with both steps):
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1)Pyruvate Dehydrogenase Complex: can be converted to Acetyl CoA to go into Citric Acid Cycle to be used for energy
2) Pyruvate Carboxylase: can be converted to OAA, which is converted to Malate or Aspartate to be used in GLUCONEOGENESIS to make glucose |
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How can amino acids and fats replenish intermediates of the TCA cycle?
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can be degraded to intermediates of the cycle... (fats)- odd chain and branched fatty acids are degraded to propionyl-CoA which is metabolized to Succinyl- CoA
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How does the purine nucleotide Cycle contribute to intermediates of the TCA cycle?
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conversion of Aspartate--> Fumarate
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