Chem4711(NoteSet9)

Chem4711(NoteSet9) - Citric acid cycle/Ox-Phos Three stages...

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Citric acid cycle/Ox-Phos Acetyl CoA as the common entry point into the citric acid cycle Three stages of cellular respiration: -make acetyl CoA -make reducing equivalents -ox-phos
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Citric Acid Cycle Primary role is to strip e - from acetyl CoA. CH 3 CO 2 H + 2 H 2 O = 4 H 2 + 2 CO 2 4 H 2 = 8 H + + 8 e - Citric acid cycle produces little energy itself BUT – feeds e - into Ox-Phos – makes lots of energy
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` Acetyl CoA: -a carrier of acetyl and other acyl groups -a “high-energy” compound -(activated acetate) -energy stored in thioester bond -about the same energy as ATP
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Pyruvate dehydrogenase Three active sites in one enzyme: E1: pyruvate dehydrogenase E2: dihydrolipoyl transacetylase E3: dihydrolipoyl dehydrogenase
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Pyruvate dehydrogenase structure
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Reaction cycle Co-enzyme menagerie -TPP -Lipoic acid -CoA -FAD -NAD
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Pyruvate dehydrogenase Picture 3
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1. Collapse of charge-transfer complex and formation of covalent adduct. 2. Nucleophilic attack by Cys43 to form disulfide and reduced flavin. 3. Rapid transfer of hydride to C4 of NAD + (not shown).
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Why a multienzyme complex? Coordinate regulaton – control the series of reactions at one locus. Channeling of intermediates – they can go directly from one E to the next without encountering solvent, other E’s, etc.(avoid side rxn problem) Increase rate at which intermediates go from one E to the next Glycosomes(parasite has it, solid mass of protein, little salt and wa Has all the enzyme of glycosis, jammed into one small organelle. Effectively multi-enzyme complex, unique type of channeling.
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Regulation of PDH 1. NADH competes with NAD + 2. Acetyl-CoA competes with CoA 1. Kinase inactivates PDC (and is itself regulated) 2. Phosphatase activates PDC (and is itself regulated)
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What happens in cell going from high to low energy? Low energy – want to make more ATP, turn on citric acid cycle. Need to increase oxaloacetate Primary sources of OAA are glucose, amino acids and odd chain fatty acids. Two acetates CANNOT be used to generate OAA! High energy – want to turn off ATP production “Siphon off” OAA and other intermediates Can convert them to sugars, amino acids, or fat.
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Very active cell ATP drops, glycolysis increases Rate of citric acid cycle and OxPhos increases BUT – OxPhos becomes rate limiting Now NADH increases – decreases flow through citric acid cycle and pyruvate builds up. Strain of excess pyruvate releaved by oxidizing NADH to NAD + and reducing pyruvate to lactate. Acidification releases more O 2 . Excess acidification becomes painful.
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Why are blockages in blood vessels bad for the heart? - O 2 drops, can’t make ATP via Ox-Phos - Glycolysis increases, citric acid stops - Cells produce lactate to keep glycolysis going, become acidic - ATP levels drop rapidly - Ion pumps slow down, normal ion gradients decrease. - Cells swell, become more acidic.
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This note was uploaded on 02/23/2011 for the course CHEM 4711 at Colorado.

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Chem4711(NoteSet9) - Citric acid cycle/Ox-Phos Three stages...

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