Question

What is cyclic about the reactions that make up the Krebs cycle?

A. The molecules that start the reaction are circular.

B. The molecules that end the reaction are circular.

C. The first reactant and last product are the same.

D. The reactions start without any outside energy.

Answer 1

In the Kreb cycle, energy is needed so D is wrong. The first reactant and last product are the same which causes it to be cyclic so the answer is C

Answer 2

The correct answer would be C. The first reactant and last product are the same.

Cyclic reactions are the reactions in which the reactant is regenerated at the end of process in order to repeat the reaction again.

For example, in Krebs cycle oxaloacetate is the reactant used in the first step of the cycle. It accepts acetyl group of acetyl-CoA to form citrate. Citrate then undergoes various steps to produce carbon dioxide (waste product), NADH, and GTP.

Oxaloacetate is then regenerated at the last step of the cycle where malate is dehydrogenated to form oxaloacetate with the help of malate dehydrogenase. It also results in the formation of NADH + H⁺ from NAD⁺.