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61 Cards in this Set
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- Back
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in all cells functioning aerobically, pyruvate is oxidized to what?
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Acetyl-CoA
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What serves as the interface between stage II and stage III metabolism?
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pyruvate dehydrogenase
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PDH is what type of a subunit complex?
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a multisubunit complex
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What happens to pyruvate in PDH1?
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pyruvate dehydrogenase accepts pyruvate and decarboxylates it to form a hydroxyethyl derivative bound to the reactive carbon of thiamine(Vit. B1) pryophosphate, the coenzyme of pyruvate decarboxylase.it is then transferred to PDH II
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vitamins are precursors of cofactors in what type of reactions?
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energy yielding reactions
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What is PDH II also called?
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dihydrolippoyl transacetylase
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what does PDH II have covalently attached to the core protein?
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lipoic acid
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What happens to the hydroxyethyl intermediate at PDH II?
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*it is oxidized by transfer to the disulfide form of lipoic acid covalently bound to dihydrolipoyl transacetylase.
*the acetyl group bound as a thioester to the side chain of lipoic acid is transferred to CoA, releasing acetyl-CoA to the medium. |
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B/c lippoic acid carries the hydroxyethyl group as a thio-ester and transfers it to CoA, another thiol, it is called what type of transfer?
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transthioesterification
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What does PDH III do to PDH II?
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*it recycles it so that it can serve as a hydroxyethyl acceptor again
*it reoxidizes the lippoic acid by FAD-dependent dihydrolipoyl dehydrogenase and ultimately uses NAD+ as an electron and a proton acceptor. *entire complex releases acetyl-CoA - molecule having a high group transfer potential for Acetate into the matrix of the mitochondria |
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what is PDH III called?
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dihydrolippoyl dehydrogenase
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mitochondrial catabolic pathways produce what?
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acetyl-CoA
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How is acetyl-CoA formed in the mitochondrial catabolic pathways?
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*oxidation of fatty acids
*oxidation of ketone bodies *oxidation of AA carbon skeletons |
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the PDH complex is important in regulating the flux of what?
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carbohydrate derived material into the mitochondria
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how does PDH serve as a fuel selector valve?
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it restricts the amount of carbohydrates used in the presence of other fuels
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what are preferred energy sources of PDH?
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fatty acids and ketone bodies
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how is PDH inhibited?
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1. PDH is covalently modified by phosphorylation and inhibited in the presence of elevated ATP
2. PDH I allosterically blocked by high levels of acetyl-CoA and NADH 3. PDH II inhibited by high levels of acetyl-CoA 4. PDH III inhibited by high levels of NADH |
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the inhibition by ATP allows the PDH complex to block what?
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carbohydrate used when the cell is not in need of energy
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the inhibition by acetyl-CoA allows the PDH complex to what?
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slow down when other fuels are producing adequate acetyl-CoA
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the inhibition by NADH allows the PDH complex to what?
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slow down when coupled NADH-utilizing pathways are swamped
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what 3 fates may pyruvate suffer?
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1. reduction to lactate in animals and bacteria
2. oxidation to acetyl-CoA in all aerobic organisms 3. decarboxylation and reduction to ethanol in yeast *all 3 reactions regenerate NAD+ |
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when pyruvate is converted to ethanol, the pathway is dependent on what?
where does this pathway take place? |
thiamine pyrophosphate
cytosol |
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pyruvate is converted to lactate in what type of cells?
where does this pathway take place? |
cells with few or no mitochondria - RBC, WBC, and in skeletal muscle during intense exercise.
cytosol |
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the formation of lactate from pyruvate can be reversed in what type of tissues?
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tissues with a low NADH/NAD+, ex. liver and heart muscle
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PDH complex is located where?
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mitochondria
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What are the coenzymes in the PDH complex?
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Thiamine-PP, lipoic acid, FAD,NAD+, and CoA
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PDH is a source of acetyl-CoA for what?
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TCA and fatty acid synthesis
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are the reactions of pyruvate carboxylase and PDH reversible or irreversible?
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irreversible
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pyruvate carboxylase is localized where?
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mitochondria
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pyruvate carboxylase replensishes intermediates for the ______ cycle and provides substrates for ______
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TCA ; gluconeogenesis
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pyruvate carboxylase is activated by ________ and _______ serves as a prosthetic group
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acetyl-CoA ; biotin
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in anaerobic metabolism what happens to pyruvate?
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it is reduced to lactate by lactate dehydrogenase:
pyruvate + NADH goes to lactate + NADH+ + H+ |
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in hypoxic muscles there is pain why?
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b/c lactate accumulates lowering the pH
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Lactate dehydrogenase allows glycolysis to proceed anaerobically by producing what?
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NAD+ for G3PDH
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in severe alcohol intoxification, patients develop what?
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lactic acidosis
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what are the 2 isoenzymic forms of lactate dehydrogenase?
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1. H4- found in heart and RBCs, has low Km for lactate and allows heart to utilize lactate as fuel
2. M4- predominates in skeletal muscle, readily converts pyruvate to lactate under hypoxic conditions |
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LD is released as a result of damage to what?
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tissue
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what is the basic building block of citrate?
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oxaloacetate
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how is citrate formed?
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why does citrate synthesis need to be regulated? what is it regulated by?
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b/c it has a highly neg. change in G ; allosterically inhibited by NADH and Succinyl-CoA
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Can citrate cross the mitochondrial membrane? What does citrate inhibit?
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Yes ; glycolysis
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How is citrate isomerized to isocitrate?
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*aconitase removes water and then re-adds it to move a hydroxyl group from C-2 to C-3
*aconitase is an equilibrium controlled enzyme *cis-Aconitic Acid is an intermediate *an iron-sulfur center is important |
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what happens to isocitrate?
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it is oxidatively decarboxylated to alpha-ketoglutarate and yields NADH. isocitrate dehydrogenase mediates a highly neg. change in G and serves as the primary control of the cycle process
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How is ICDH regualted?
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1. covalently inhibited by ATP
2. allosterically inhibited by NADH 3. inactive without ADP 4. NAD+ limitiation reduces activity *similar to PDH regulation |
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ICDH has a structure similar to what?
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PDH
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alpha-ketoglutarate dehydrogenase has a similar structure to PDH but is what?
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poorly organized
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how is succinyl CoA formed?
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succinyl-CoA has a high group transfer potential for what?
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succinate
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what reduces the amount of energy released by the reaction forming succinyl-CoA?
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formation of NADH - has a high group transfer potential for electrons and protons
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how is succinate formed from succinyl-CoA?
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succinyl-CoA is cleaved to form succinate, the energy released is used to phosphorylate GDP to GTP.Not quite enough energy to make NADH.succinyl-CoA synthase caries out substrate level phosphorylation
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Why is GTP compartmentalized to a different set of enzymes than ATP?
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b/c the enzyme recognition site is different
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succinyl-CoA synthase is similar to phosphoglyceryl kinase of glycolysis why?
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b/c it also forms a triphospahte - in this case GTP
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the rate GTP is formed by succinyl-CoA synthase is controlled how?
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equilibrium controlled
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Succinate Dehydrogenase
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*a flavoprotein
*oxidizes succinate to fumarate *located in inner mitochondrial membrane *identical to complex II of ETS *complex is sometimes called succinate-CoQ reductase *electrons are captured by FAD to form FADH2 *FADH2 reduces Fe-S centers, Fe-S center reduce Coenzyme Q |
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How is fumarate converted to malate and then malate converted to oxaloacetate?
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*fumarate is hydrated to malate by fumarase, an equilibrium controlled enzyme
*malate is oxidized to oxaloacetate releasing a NADH into the matrix *malate dehydrogenase catalyzes a highly endergonic reaction |
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How does the malate shuttle bring NADH into the mitochondria?
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malate crosses the inner mitochondrial membrane and is oxidized to form OAA, releasing a NADH into the matrix
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OAA can be produced where?
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inside and outside the mitochondria - OAA levels inside the mitochondria are generally low
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the TCA cycle extracts how much energy from glucose?
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3% - very little
acetyl-CoA + 3NAD+ + FAD + GDP + Pi +2H2O = 2CO2 + 3NADH + 3H+ + FADH2 + GTP + CoASH |
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the TCA cycle is called a ______ or _______ cycle
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filling up or anaplerotic
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T or F the TCA cycle utilizes and makes many intermediates used in other pathways
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T
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The TCA cycle finishes the convergence of pathways to one pathway and makes one important product which is what?
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NADH
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