The citric acid is a stage of catabolism that oxidizes acetate into carbon dioxide and generates energy. There are eight enzymes involved in the citric acid cycle.
1. Which enzymes produce NADH as a product?
a. alpha-ketoglutarate dehydrogenase
b. succinate dehydrogenase
c. malate dehydrogenase
d. isocitrate dehydrogenase
2. Which enzymes produce carbon dioxide as a product? Select all that apply.
a. malate dehydrogenase
b. isocitrate dehydrogenase
c. succinate dehydrogenase
d. alpha-ketoglutarate dehydrogenase
3. Which enzymes produce coenzyme A as a product? Select all that apply.
a. fumarase
b. citrate synthase
c. succinyl-CoA synthesase
d. citraste synthase
4. Which enzymes have an alpha-keto acid substrate? Select all that apply.
a. fumarase
b. alpha-ketoglutarate dehydrogenase
c. citrate synthase
d. malate dehydrogenase
5. Which enzyme catalyzes a hydration reaction?
a. aconitase
b. fumarase
c. citrate synthase

The citric acid cycle is responsible for the oxidation of acetyl-CoA produced from pyruvate from glycolysis. The citric acid cycle has eight steps requiring nine enzymatic reactions involving eight enzymes.

The enzymes in the citric acid cycle are: citrate synthase , aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase , succinyl-CoA synthesase, succinate dehydrogenase , fumarase , and malate dehydrogenase .

1. The dehydrogenation reactions of isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase , and malate dehydrogenase produces NADH from isocitrate, alpha-ketoglutarate and malate respectively.

2. Oxidative decorboxylation (removal of carbon as CO₂) also occurs in the reactions of isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase to produce alpha-ketoglutarate and succinyl-CoA respectively.

3. Coenzyme-A (CoA-SH) is produced in the reactions of citrate synthase and succinyl-CoA sythetase to produce citrate and succinate respectively.

4. The enzymes alpha-ketoglutarate dehydrogenase has alpha-ketoglutarate as substrate , whereas citrate synthase and malate dehydrogenase has oxaloacetate as substrate. These substrates are alpha-keto acids.

5. Aconitase catalyzes the conversion of citrate to isocitrate by first a dehydration and then a hydration reaction.