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29 Cards in this Set
- Front
- Back
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Most of the energy contained in metabolic fuels is conserved in the chemical bonds (electrons) of?
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Acetyl-CoA
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Thermodynamic variables: G, H, S, T, R, F
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G = free energy (energy available to do work)
H = enthalpy (heat content of a compound) S = entropy (randomness of a system) T = absolute temperature (measured in degrees Kelvin) R = gas constant (1.987 cal/mol(degree)) F = Faraday's constant (23 kcal/volt(mol)) |
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a) If deltaG is less that 0 = ?
b) If deltaG is greater than 0 = ? c) If deltaG = 0? |
a) spontaneous rxn (exergonic)
b) nonspontaneous rxn (endergonic) c) @ equilibrium (forward and reverse rxns are equal) (deltaG = the energy difference between the products and reactants --> Gprod. - Greact.) |
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Substrate-level phosphorylation
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The conversion of ADP to ATP by the use of high-energy phosphate metabolites (those with higher phosphate bond energy than ATP)
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What are the only 3 phosphorylated intermediates in cells with sufficient energy to participate in substrate-level phosphorylation?
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-PEP (phosphoenolpyruvate)
-1,3-Bisphosphoglycerate -Creatine phosphate *top two = intermediates in glycolysis; creatine phosphate = energy reservoir in muscle |
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Compounds with MORE NEGATIVE reduction potentials have a tendency to?
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REDUCE (donate eelectrons to) compounds with less negative reduction potentials.
More positive (+) = more likely to be the electron acceptor More negative (-) = more likely to be the electron donor |
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If the reduction potential is given, how do you determine the oxidation potential?
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Reverse the sign from - to +
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For a reaction to be exergonic, the reduction potential (E) must be?
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positive (+)
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3 major electron carriers?
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NAD+, FAD, NADPH
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What is NAD+?
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The electron acceptor in rxns involving oxidation of hydroxylated carbon atoms. It accepts a hydride ion (H-) to form NADH and the hydroxyl group is oxidized to a carbonyl group.
* H-C-OH + NAD+ --> C=O +NADH + H+ |
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What is FAD?
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Electron acceptor in rxns involving the oxidation of two adjacent carbons, resulting in the formation of a C=C bond. A hydrogen atom is removed from each C atom and is transferred to FAD to form FADH2.
*C-C +FAD --> C=C +FADH2 |
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What is NADPH?
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The major source of reducing power for biosynthetic pathways. Unlike NADH, which is generated and used primarily in mitochondria, NADPH is formed and used in extramitochondrial rxns.
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In the CAC, each acetyl-CoA generated from pyruvate is used to produce?
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-3 NADH
-1 FADH2 -1 GTP |
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What is the major catabolic function of the CAC?
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To transfer electron pairs (potential energy) from acetyl-CoA to NADH and FADH2. For every turn of the cycle, two C's enter as acetyl-coA, two carbons leave as CO2, and the four pairs of electrons in the C-H and C-C bonds are transferred to NADH and FADH2.
One high-energy phosphate bond (GTP) is produced by substrate-level phosphorylation. Assuming adequate O2 is available, subsequent oxidation of NADH and FADH2 will result in the synthesis of 11 molecules of ATP by ox-phos. Therefore the complete oxidation of one acetyl-coA yields 12 ATP equivalents. |
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What is the major anabolic function of the CAC?
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Production of:
-citrate (substrate for FA synthesis) -oxaloacetate (first intermediate in gluconeogenesis) -succinyl-coA (required for the synthesis of heme) -oxaloacetate and alpha-ketoglutarate (substrates for AA synthesis) |
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All of the enzymes involved in the CAC are located in the mitochondrial matrix, except for -----------, which is located -----------?
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succinate dehydrogenase; inner mitochondrial membrane
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CAC intermediates mnemonic:
Citric Acid Is Kreb's Starting Substrate For Mitochondrial Oxidation. |
Citrate
cis-Aconitate Isocitrate alpha-Ketoglutarate Succinyl-coA Fumarate Malate Oxaloacetate |
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What are the 4 key enzymes in the CAC? Why are they important?
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The 4 dehydrogenases:
-isocitrate dehydrogenase -alpha-ketoglutarate dehydrogenase -succinate dehydrogenase -malate dehydrogenase They are important b/c they all catalyze oxidation reactions (catabolic) that create the NADH's and the FADH2. |
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What is the function of pyruvate dehydrogenase? What inhibits and activates it?
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It converts pyruvate to acetyl-coA.
Inhibitors: ATP, acetyl-coA, NADH Activators: ADP, CoASH, NAD+, Ca++, insulin |
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What is pyruvate carboxylase and why is it important?
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It converts pyruvate (3C) to oxaloacetate (4C). It is important b/c it is responsible for the rxn that replenishes the CAC of intermediates that have been removed for synthetic purposes. Acetyl-coA cannot be oxidized without a continuous supply of oxaloacetate.
*this is called an "anaplerotic" reaction *the reaction requires biotin and bicarbonate *also requires acetyl-coA as an allosteric activator of pyruvate carboxylase (i.e. if acetyl-coA builds up, it triggers this rxn) |
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Where do NADH and FADH2 enter the ETC?
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NADH = complex I
FADH2 = CoQ (betweem complexes I and II) |
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How do NADH electrons produced in the cytosol enter the mitochodria?
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Through the malate and the alpha-glycerol phosphate shuttles. NADH's do not actually cross over - only the electrons they're carrying.
Malate shuttle = incorporate electrons into mitochondrial NADH alpha-glycerol phosphate shuttle = incorporates electrons into mitochondrial FADH2 |
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What is the P/O ratio and what are the P/O values for NADH and FADH2, respectively?
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P/O ratio = the number of ATP molecules produced per O atom reduced.
NADH = 3 FADH2 = 2 |
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Why do they say that the efficiency of oxidative phosphorylation (ox-phos) is only 40%?
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Because the oxidation of NADH by the ETC releases a total of 53 kcal of energy, the synthesis of ATP requires 7.3 kcal, yet only 3 moles of ATP are produced per mole of NADH.
It should produce more like 7 moles of ATP. |
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Which is the only ETC complex that does NOT pump protons?
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Complex II
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What is the chemiosmotic hypothesis?
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It asserts that the protomotive force associated with the proton gradient drives the synthesis of ATP.
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Which complex is known as ATP synthase?
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Complex V
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What are the two subunits of ATP synthase?
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Fo = spans the membrane, creating a proton channel that allows protons to move back into the matrix.
F1 = protrudes into the matrix and, in the presence of a proton gradient, catalyzes the condensation of ADP and Pi to form ATP. |
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What happens to the ETC and, thus, the CAC if oxygen is low?
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Ox-phos decreases and NADH and FADH2 begin to accumulate, thereby inhibiting the CAC. This coordination is known as "respiratory control".
If adequate O2 is available, then it all depends on the availability of ADP. |
