TCA Cycle Flashcards
Where does the Tricarboxylic Acid (TCA) Cycle occur?
In the mitochondrial matrix
The TCA cycle is a part of
Cellular respiration (aerobic process)
The TCA consists of a series of ______ reactions that results in ________ to ___________
REDOX, oxidation of acetyl-CoA, 2 molecules of CO2
4C (OA) + 2C (acetyl) –>
6C (citrate)
Isomer of citrate is “oxidatively decarboxylated” to give
5C compound (alpha-Ketoglutarate)
5C compound (alpha-Ketoglutarate) –>
4C (succinate) via oxidative decarboxylation
OA is regenerated from
succinate (the cycle repeats)
Label
Properties of the TCA cycle:
- Aerobic
- Source of biosynthetic precursors
- Its activity depend of tissue type: Most active in brain, heart, kidney cortex, and liver
- Subcellular location: Enzymes within mitochondrial matrix except succinate dehydrogenase, which is located on the mitochondrial inner membrane.
- Compartmentalization - Inner mitochondrial membrane is impermeable to NADH, Acetyl CoA, Oxaloacetate; separate mitochondrial & cytosolic pools of each.
Enzymes of the TCA Cycle
- Citrate synthase
- Aconitase
- Isocitrate dehydrogenase
- Alpha-ketoglutarate dehydrogenase complex
- Succinyl-CoA synthetase
- Succinate dehydrogenase
- Fumarase
- Malate dehydrogenase
Pyruvate Dehydrogenase Complex (in mitochondrial matrix; not part of TCA cycle) consists of :
E1, pyruvate dehydrogenase (decarboxylation, TPP)
E2, dihydrolipoyl transacetylase (lipoamide, CoA)
E3, dihydrolipoyl dehydrogenase (FAD, NAD+)
Other components (regulatory): PDH kinase, protein phosphatase
Last 3 steps that constitute a common “metabolic motif”
Oxidation→hydration→oxidation
TCA Cycle is regulated:
- By energy charge: ATP, ADP
- By end product of the cycle: mitochondrial NADH
- At irreversible steps
Irreversible steps cataylized by
–citrate synthase
–isocitrate dehydrogenase (major)
–alpha-ketoglutarate dehydrogenase
Citrate synthase is allosterically regulated by
–NADH, succinyl-CoA, citrate, and ATP (inhibitors)
–ADP (activator)
