Question

The citric acid cycle is a stage of catabolism that oxidizes acetate into carbon dioxide and generates energy. There are eight enzymes involved in the citric acid cycle. Which enzymes produce NADH as a product? succinate dehydrogenase isocitrate dehydrogenase malate dehydrogenase α‑ketoglutarate dehydrogenase Which enzymes produce carbon dioxide as a product? α‑ketoglutarate dehydrogenase malate dehydrogenase succinate dehydrogenase isocitrate dehydrogenase Which enzymes produce coenzyme A as a product? succinyl‑CoA synthetase citrate synthase succinic dehydrogenase fumarase Which enzymes have an α‑keto acid substrate? malate dehydrogenase citrate synthase fumarase α‑ketoglutarate dehydrogenase Which enzyme catalyzes an isomerization?

Answer 1

Answer:

1. isocitrate dehydrogenase,  malate dehydrogenase,  α‑ketoglutarate dehydrogenase

2. α-ketoglutarate dehydrogenase and Isocitrate dehydrogenase

3. Succinyl coenzyme A synthetase

4. α‑ketoglutarate dehydrogenase

5. aconitase

Explanation:

The citric acid cycle is a stage of catabolism in which the oxidation of acetyl-CoA takes place which releases stored energy. it takes place in the matrix of the mitochondria (in eukaryotes) or in cytoplasm (in prokaryotes).

1. All the  dehydrogenase produces NADH in citric acid cycle except succinate dehydrogenase as it inhibit other dehydrogenase enzymes activity. so, Isocitrate dehydrogenase (in second step),  α‑ketoglutarate dehydrogenase (in third step) , and malate dehydrogenase (in eigthth step or final step)  are responsible to produces a coenzyme, NADH.

2.  Isocitrate dehydrogenase (in third step) form one carbon dioxide and one NADH and α-ketoglutarate dehydrogenase (in fourth step) form four-carbon succinyl CoA. hence both the enzymes  produces carbon dioxide in the citric acid cycle.

3. Succinyl coenzyme A synthetase catalyzes the formation of coenzyme-A and succinate.

4. α‑ketoglutarate dehydrogenase have an α‑keto acid substrate which is converted into into a four-carbon succinyl CoA in the fourth step of citric acid cycle.

5. Aconitase catalyzes the isomerization of citrate to isocitrate.

Hence, the correct answer is:

1. isocitrate dehydrogenase,  malate dehydrogenase,  α‑ketoglutarate dehydrogenase

2. α-ketoglutarate dehydrogenase and Isocitrate dehydrogenase

3. Succinyl coenzyme A synthetase

4. α‑ketoglutarate dehydrogenase

5. aconitase