TCA - CITRIC ACID CYCLE = TCA CYCLE = KREBS CYCLE TCA =...

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CITRIC ACID CYCLE CITRIC ACID CYCLE = TCA CYCLE = KREBS CYCLE = TCA CYCLE = KREBS CYCLE TCA = tricarboxylic acid cycle Definition: -- Acetate in the form of acetyl-CoA, is derived from pyruvate and other metabolites, and is oxidized to CO 2 in the citric acid cycle.
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************************************************************ c One high energy compound is produced for each cycle. d The electrons from the TCA cycle are made available to an electron transport chainin the form of three NADH and one FADH 2 and ultimately energy is provided for oxidative phosphorylation. ************************************************************
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± The citric acid cycle is central to all respiratory oxidation, oxidizing acetyl-CoA from glucose, lipid and protein catabolism in aerobic respiration to maximize energy gain. ± The cycle also supplies some precursorsfor biosynthesis. ± All enzymes are in the mitochondrial matrix or inner mitochondrial membrane **************************************************
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The three stages three stagesof cellular respiration: Stage 1. Acetyl CoA production --from glucose, fatty acids and amino acids Stage 2. Acetyl CoA oxidation = TCA Cycle = yielding reduced electron carriers Stage 3. Electron transport and oxidative phosphorylation -- oxidation of these carriers and production of ATP ***************************************************
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Many catabolic pathways yield Many catabolic pathways yield acetyl CoA for the TCA cycle acetyl CoA for the TCA cycle glycogen Ð glucose lactate pyruvate fatty acids Ð amino acids Î Acetyl-CoA TCA TCA (Note: aa more than one entry point)
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Acetyl CoA Acetyl CoA HS-CoA Space filled Acetyl
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0- Conversion of pyruvate to acetyl-CoA -- A major Stage 1 setup Enzyme = pyruvate dehydrogenase complex pyruvate dehydrogenase complex Location = mitochondrial matrix CH 3 CH 3 C=O + NAD + + HS-CoA ¼ C=O + NADH+CO 2 COO - S-CoA Pyruvate Acetyl-CoA
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$ Irreversible -- irreversible means acetyl-CoA cannot be converted backward to pyruvate; hence “fat cannot be converted to carbohydrate”
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± Complex of 2.5 x 10 6 Da, including multiple copies of three enzymes ± pyruvate dehydrogenase (=E 1 ) has coenzyme = thiamine pyrophosphate(TPP) -- TPP is coenzyme for all decarboxylations of α -keto acids. -- lack of thiamine = beriberi ± dihydrolipoyl transacetylase (=E 2 ) has coenzymes lipoate and CoA
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± dihydrolipoyl dehydrogenase (= E 3 ) has coenzymes FAD and NAD + S-- S-- TPP FAD  E 1 E 2 E 3 N A D +
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thiamine pyrophosphate (TPP) lipoic acid aka lipoamide
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Partial reactions of PDH: c introduction of pyruvate onto TPP in E 1 hydroxyethyl-TPP HH O O CO 2 O - O-C-C-CH 3 H-CCH 3 TPP E 1 E 1
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d Transfer to lipoamide of E 2 hydroxyethyl hydroxyethyl - - TPP TPP + + O CH 3 + TPP S C S SH S E 2 E 2 lipoamide-E 2 acetyl-lipoamide-E 2 (disulfide,oxidized) (reduced) ± Note concurrent oxidation to acetyl and reduction of S
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e E 2 then transfers acetyl to CoA; acetyl-CoA leaves. f E 3 uses its bound coenzyme FAD to oxidizelipoamide back to disulfide and generating FADH 2 .
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TCA - CITRIC ACID CYCLE = TCA CYCLE = KREBS CYCLE TCA =...

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