Enzymes of the Cycle
This enzyme catalyzes the isomerization of citrate to isocitrate.
What is aconitase?
This molecule condenses with oxaloacetate to form citrate, beginning the cycle.
What is acetyl‑CoA?
This high‑energy electron carrier is produced at three different steps in the cycle.
What is NADH?
This molecule must be transported from the cytosol into the mitochondrion before entering the cycle.
What is pyruvate?
This enzyme converts isocitrate into α‑ketoglutarate while reducing NAD⁺.
What is isocitrate dehydrogenase?
This intermediate is a six‑carbon molecule formed immediately after acetyl‑CoA enters the cycle.
What is citrate?
This enzyme is strongly inhibited by ATP and NADH, slowing the cycle during high‑energy states.
What is isocitrate dehydrogenase?
This cofactor is required by both pyruvate dehydrogenase and α‑ketoglutarate dehydrogenase.
What is thiamine pyrophosphate (TPP)?
This enzyme catalyzes the oxidative decarboxylation of α‑ketoglutarate.
What is α‑ketoglutarate dehydrogenase?
This step of the cycle produces the first molecule of CO₂.
What is the isocitrate → α‑ketoglutarate step?
This intermediate accumulates when the cycle backs up due to high NADH levels, often signaling a shift toward fatty acid synthesis.
What is citrate?
This molecule links glycolysis to the citric acid cycle but is not technically part of the cycle itself.
What is pyruvate?
This enzyme produces FADH₂ instead of NADH.
What is succinate dehydrogenase?
This intermediate is formed when succinyl‑CoA loses CoA and generates GTP.
What is succinate?
This is the total number of NADH molecules produced per turn of the cycle.
What is three?
This enzyme is embedded in the inner mitochondrial membrane and also functions in the electron transport chain.
What is succinate dehydrogenase?
This enzyme hydrates fumarate to form malate.
What is fumarase (fumarate hydratase)?
This intermediate is the immediate precursor to malate.
What is fumarate?
This high‑energy molecule inhibits citrate synthase, slowing the entry of acetyl‑CoA into the cycle during energy‑rich states.
What is ATP?
This amino acid can be transaminated to form oxaloacetate, allowing anaplerotic replenishment of the cycle.
What is aspartate?