citric acid cycle / tca cycle
TRANSCRIPT
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Citric acid cycle / TCA Citric acid cycle / TCA cyclecycle
Citric acid cycle / TCA Citric acid cycle / TCA cyclecycle
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Citric acid cycle
• Krebs cycle,tricarboxylic acid.• A series of reactions in mitochondria oxidize
acetyl Co-A reduced coenzymes reoxidation in respiratory chain
• Functions:-The final common pathway for aerobic oxidation of carbohydrate, lipid, protein-A central role :
1. gluconeogenesis2. lipogenesis 3. interconversion of amino acids
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Citric acid cycle
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Citric acid cycle• Started with condensation of acetyl coA
with oxaloacetate to form citrate two molecules of CO2 released and oxaloacetate regenerated
• Oxaloacetate catalytic role• Enzymes: citrate synthase, aconitase,
isocitrate D-ase, ketoglutarate D-ase complex, succinate thiokinase, succinate D-ase, fumarase and malate D-ase
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Citric acid cycle
• Acetyl coA + Oxaloacetate + H2OCitrate + coA + H+.
• Citrate ↔ Cis aconitate + H2O• Cis aconitate + H2O ↔ Isositrate
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• Isositrate + NAD+ ↔ αKetoglutarate + CO2 + NADH
• α-Ketoglutarate + NAD+ + CoA ↔Succinyl coA + CO2+NADH
• Succinyl coA + Pi + GDP ↔ Succinate + GTP + coA.
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• Succinate + FAD ↔ Fumarate + FADH2.
• Fumarate + H2O ↔ Malate• Malate + NAD+ ↔ Oxaloacetate +
NADH + H+
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Citric acid cycle• Result of oxidations: 3 NADH and FADH2
in one turn of cycle• 1 ATP or GTP formed by substrate level
phosphorylation• B vitamins involved:
- riboflavin- niacin - thiamin - pantothenic acid
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• Riboflavinto form FAD cofactor in the α-ketoglutarat deh. Complex & Succinate deh.
• Niacinto form NADcoenzyme for isocitrate deh.,α-ketoglutarat deh.,malate deh.
• ThiaminThiamin diphosphate coenzyme for decarboxylation in the α-ketoglutarat deh.
• Panthothenic acid as part of coA, cofactor attached to active carboxylic acid residues (acetyl coA, Succinyl coA)
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Roles in matabolism• Amphibolic oxidative and synthesis
processes1. Gluconeogenesis: all intermediates
potentially glucogenic (give rise to OA production of glucose)
• Substrates for gluconeogenesis:- lactate- glycerol- glucogenic amino acids- propionate
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Roles in matabolism2. Transamination by aminotransferase:
a source of carbon skeletons for synthesis of some amino acids reversible form some intermediates from these amino acids:-aspartate + pyruvate OA + alanine-glutamate + pyruvate keto glut + alanine
3. Acetyl coA is the major building block for long chain fatty acid synthesis
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Citric Acid Regulating• Depends on : NAD+,FAD, ADP• Key enzimes :
Citrate synthaseisocitrate dehydrogenase,α ketoglutarat dehydrogenase