Question

Which of the following enzymes do not catalyze a reaction in the citrate cycle that produces CO2 as a product?

Choose one or more:
A. isocitrate dehydrogenase
B. fumarase
C. succinate dehydrogenase
D. succinyl-CoA synthetase

Answer 1

Fumarase and succinate dehydrogenase are the enzymes in the citrate cycle that do not catalyze reactions resulting in the production of CO2. C. succinate dehydrogenase

Step-by-step explanation:

The enzymes in the citrate cycle which do not catalyze a reaction that produces CO2 as a product are fumarase and succinate dehydrogenase. Fumarase catalyzes the hydration of fumarate to L-malate and does not involve the release of CO2.

Similarly, succinate dehydrogenase catalyzes the oxidation of succinate to fumarate without releasing CO2. On the other hand, isocitrate dehydrogenase catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate, which does result in CO2 release, and therefore is not an enzyme that fits the criteria of the question. Succinyl-CoA synthetase converts succinyl-CoA into succinate, but this reaction also does not produce CO2.

Answer 2

In the citrate cycle, fumarase, succinate dehydrogenase, and succinyl-CoA synthetase are enzymes that do not catalyze reactions that produce CO2. Isocitrate dehydrogenase is the only enzyme among the options listed that does produce CO2 as one of its reaction products. So, the correct options that do not catalyze a reaction producing CO2 in the citrate cycle are options B (fumarase), C (succinate dehydrogenase), and D (succinyl-CoA synthetase).

Step-by-step explanation:

The student's question inquires about which enzymes in the citrate cycle do not produce CO2 as a product. The citrate cycle, also known as the Krebs cycle or TCA (tricarboxylic acid) cycle, is a series of enzymatic reactions that play a central role in cellular respiration. During the cycle, compounds are oxidized and decarboxylated, and energy is produced in the form of ATP, NADH, and FADH2.

Enzymes like isocitrate dehydrogenase catalyze reactions that do generate CO2 by converting isocitrate into alpha-ketoglutarate, while others such as aconitase and succinyl-CoA synthetase are involved in reactions that do not directly release CO2. Specifically, aconitase catalyzes the conversion of citrate to isocitrate, and succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate without the release of CO2. However, succinate dehydrogenase oxidizes succinate to fumarate without releasing CO2. Additionally, fumarase hydrates fumarate to malate, also without releasing CO2. Given this information, the correct options that do not catalyze a reaction producing CO2 in the citrate cycle are options B (fumarase), C (succinate dehydrogenase), and D (succinyl-CoA synthetase). In contrast, isocitrate dehydrogenase (option A) does produce CO2 and is not an answer to this question.