The citric acid cycle (TCA: Trucarvixylic cycle)
14 important questions on The citric acid cycle (TCA: Trucarvixylic cycle)
What is pyruvate dehydrogenase (PDH)?
- Links glycolysis to the TCA cycle via pyruvate dehydrogenase complex
- reaction is irreversible (regulation)
- converts pyruvate to acetyl-CoA (oxidative decarboxylation, CO2 out!)
- Most important point since it is the entry of substrates into the TCA cycle
Where/When does the citric acid cycle/TCA happen?
- Mitochondira
- it is the final pathway of oxidation of fuels (carbohydrate, fatty acids, amino acids) which release stored energy
What is the overal reaction input/output?
- 1 Acetyl-CoA (C2)
output
- 3 NADH
- 1 FADH2
- 1 GTP
- (2 CO2)
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What is the pathway to get ATP?
Glycolysis (aerobic), TCA cycle, beta-oxidation (fatty acids)
- Resulting in reduced co-enzymes (NADH, FADH2)
- Respiratory chain, ATP synthase (oxidative phosphorylation)
- uses O2
What is TCA cycle?
- Coupling to respiration
- is a series of oxidation/reductions
- oxidation of 1 Acetyl group (C2) to 2x CO2
- Harvesting "high-energy" electrons
- Which are used for ATP synthesis
Explain the anaerobic glycolysis, how is the TCA cycle involved in it?
- Coupling to Lactate dehydrogenase (LDH) where pyruvate is converted to lactate, where NAD+ produced by it is used to form ATP
Where in the TCA cycle does the condensation and the 2 oxidative decarboxylation take place?
- Acety-CoA to citrate citrate synthase
Oxidative decarboxylation (CO2 out!)
- Isocitrate to alfa-ketoglutarate Isocitrate dehydrogenase
- alfa-ketoglutarate to succinyl-CoA alfa-ketoglutarate dehydrogenase complex
What are the control points in TCA?
- Pyruvat dehydrogenase
inhibition: ATP, acetyl CoA, NADH
- activation: ADP, pyruvate
- Isocitrate dehydrogenase
- inhibition: ATP, NADH
- Activation: ADP
- alfa-ketoglutarate dehydrogenase
- inhibition: ATP, succinyl CoA, NADH
What an anapleurotic reaction?
- When one of the TCA cycle intermediates is added into the cycle that have been extracted from biosynthesis (E, in exemple)
- Pyruvate carboxylase could carboxylate pyruvate to oxaloacetate, giving the cycle more C4 compounds to condense with incoming C2 compounds
What is an catapleurotic reaction?
- When you use/steal C4 intermediates from the TCA for biosynthesis
- Aspartate biosynthesis also requires oxaloacetate, so when aspartate is synthesized the result is less net oxaloacetate. So when a catapleurotic reaction occur, there is less oxaloacetate to condens with acetyl CoA
- when there is not enough oxaloacetate, anapleurotic or filling-up reations are necessary
Which are the glucogenic amino acids forming oxaloacetate?
Which are the glucogenic amino acids forming Pyruvate?
- Alanine
- Cysteine
- Glycine
- Serine
- Threonine
- Tryptophan
Which are the glucogenic amino acids forming alfa-ketoglutarate?
- Arginine
- Glutamine
- Histidine
- Proline
Which are the glucogenic amino acids forming Succinyl CoA?
- Isoleucine
- Methionine
- Threonine
- Valine
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