The Citric Acid Cycle Flashcards
Where does TCA cycle occur?
Occurs in the mitochondrial matrix
Traffic circle analogy
- catabolism of amino acids generate cycle intermediates
- intermediates provide building blocks for amino acid synthesis
- intermediates also function in formation of glucose from a.a
Conversion of Pyruvate to Acetyl-CoA
- Under aerobic conditions pyruvate produced by glycolysis
- transported to mito. matrix and converted to acetyl-CoA
- enzyme called pyruvate dehydrogenase complex
PDH is a key regulatory step
Rxn is irreversible
- Commiting pyruvate to 1 of 2 fates
(CO2/fatty acid)
Pyruvate Dehydrogenase Rxn
Pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate
Allosteric Regulation of PDH complex
High energy change- increased conc. of NADH, Acetyl CoA, ATP
Low enerdy change- increased conc. of pyruvate, ADP
Covalent regulation of PDH complex
- kinase makes active PDH, inactive
- phosphatase makes inactive PDH, active
PDH activity stimulated when energy is low
- Phosphatase activity is stimulated by Ca 2+
- Kinase activity is inhibited by molecules indicating low energy
- ADP
- Pyruvate
PDH is switched off when energy is high
Kinase is activated by molecules indicating a hgih energy charge
- NADH
- ATP
- Acetyl-CoA
Phase 1 of TCA
- 2 C atoms are ox. and energy rich electrons are gathered as NADH
Phase 2 of TCA
Regenerates oxaloacetate and harvests more energy rich e-
Regulation of TCA
- Pyruvate dehydrogenase complex (PDH)
- Citrate Synthase
- Isocitrate dehydrogenase
- a-ketoglutarate dehydrogenase complex
(activated by low energy, inhibited by high energy)
Net production from TCA
- 2 C’s enter as acetyl-CoA and leave as CO2
- All other intermediates are recycles
Primary regulation of TCA
ATP and NADH conc.
TCA intermediates need to be replenished
- Pyruvate carboxylase regenerates oxaloacetate from pyruvate
- Active in presence of Acetyl CoA
