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29 Cards in this Set
- Front
- Back
What are the molecules in the Creb cycle from AcCoA to Oxaloacetate?
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-AcCoA
-Citrate -Isocitrate -α-ketoglutarate -Succinyl CoA -Succinate -Fumarate -Malate -Oxaloacetate |
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Do α or beta decarboxylations happen easily?
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Beta decarboxylations happen easily and spontaneously.
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What 3 enzymes are encompassed in the pyruvate dehydrogenase complex (PDC)?
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E1, pyruvate decarboxylase (contains TPP)
E2, transacetylase (contains lipoic acid) E3, dihydrolipoyl dehydrogenase (contains FAD) |
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What is the net reaction for PDH complex? Easily reversible?
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Pyruvate- + NAD+ + CoASH (yields) acetyl-CoA + CO2 + NADH
(This reaction is kinetically and thermodynamically irreversible) |
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What is the most common vitamin deficiency in alcoholics? What is this needed for?
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Thiamine- necessary to accomplish difficult α-decarboxylation reactions.
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How is PDC (pyruvate dehydrogenase complex) regulated? What is active?
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Regulated by phosphorylation/dephosphorylation. Phosphorylated PDC is inactive, dephosphorylated PDC is active.
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What increases the dephosphorylation (activation) of PDC (pyruvate dehydrogenase complex)? What decreases the phosphorylation (inactivation) of PDC?
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-Ca2+
-ADP and pyruvate |
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What increases the phosphorylation (inactivation) of PDC (pyruvate dehydrogenase complex)?
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-NADH, AcCoA (recall that these are the products of pyruvate-->AcCoA)
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Where is pyruvate converted to AcCoA?
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In the mitochondria
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What is Leigh syndrome? What is a sign of it?
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-There is a defect in the PDC (pyruvate dehydrogenase complex). This prevents pyruvate from being converted to AcCoA, therefore all metabolism is anaerobic.
-First presents in neural tissue because it can't oxidize fatty acids. -Lactic acid/pyruvate in urine, CSF, and blood |
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How does thiamine pyrophosphate (found in pyruvate decarboxylase, E1 in PDC) get around the problem of pyruvate being a α-keto acid?
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-Thiamine loses a proton (pulled off by a base on the enzyme), creating a reactive carbon.
-The carbanion attacks the carbonyl carbon of pyruvate forming a covalent intermediate. -This covalent intermediate looks more like a beta-keto acid, therefore the carboxyl group comes right off. -E2 and E3 will do the rest of the reaction. :-) |
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What is the net yield from Steps 1-8 of the Creb cycle?
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3NADH
1GTP 1FADH |
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What does the structure of citrate look like?
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6 carbons structure with 3 carboxylic acids together.
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What one enzyme in the Citric acid cycle is not found in the mito matrix?
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Succinate dehydrogenase
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What keeps the cycle turning? (3 things)
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-NADH is being used up by muscles, pulling along.
-All intermediates available, pushing through. -Energy of the reactions are favorable moving ahead. (MTF) |
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What 3 steps in the citric acid cycle release a large amount of free energy?
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Step 1, creating citrate.
Step 3, creating alpha-ketoglutarate. Step 4, creating succinyl CoA. These are also the steps that regulation occurs. |
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What kind of enzyme is used if the reaction releases either NADH or FADH?
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Dehydrogenase
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What kind of enzyme is used if ATP or GTP is created or used?
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A kinase.
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What is the significance of transforming citrate to isocitrate?
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Makes it a beta-ketone so CO2 comes right off. (Beta-decarboxylation)
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What stimulates Step 3 of Creb cycle, forming alpha-ketoglutarate from isocitrate? What inhibits it?
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-ADP, Ca2+ stimulates
-NADH inhibits |
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What does it mean that the TCA cycle is an amphibolic hub?
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This means that the TCA cycle is involved in anabolic and catabolic processes. Within the cycle itself, it fluxuates between a 6C and a 4C molecule and it also sends intermediates to other anabolic pathways.
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Besides continuing through the TCA cycle, where else can citrate go?
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To fatty acid synthesis in the cytoplasm.
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Besides continuing through the TCA cycle, where else can alphaketoglutarate go?
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-Amino acid synthesis
-Produce neurotransmitters (GABA!) |
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Besides continuing through the TCA cycle, where else can succinyl CoA go?
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To heme synthesis
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Besides continuing through the TCA cycle, where else can malate go?
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To gluconeogenesis in the liver.
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Besides continuing through the TCA cycle, where else can oxaloaccetate go?
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To amino acid synthesis
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What is an anaplerotic reaction?
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An anaplerotic reaction forms intermediates in the TCA cycle. The most important anaplerotic reaction is the conversion of pyruvate to oxaloacetate catalyzed by biotin-dependent pyruvate carboxylase. This provides oxaloacetate to react with AcCoA (normal pathway from pyruvate) to jumpstart the TCA cycle.
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Once you've formed pyruvate through glycolysis, what two directions can it go into the TCA cycle?
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It can either be converted to AcCoA by the PDC complex -or- it can be converted to oxaloacetate by biotin-dependent pyruvate carboxylase.
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Besides pyruvate, what else can contribute AcCoA to the TCA cycle?
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-Carbs
-Fatty acids -Amino acids |