1. Coenzyme A is one of the five coenzymes are used to facilitate the flow of ca
ID: 215444 • Letter: 1
Question
1. Coenzyme A is one of the five coenzymes are used to facilitate the flow of carbon from glycolysis to the citric acid cycle. Which of the following accurately describes how Coenzyme A is used?
a. Coenzyme A is required for the step that decarboxylates pyruvate.
b. Coenzyme A oxidizes hydroxyethyl TPP.
c. Coenzyme A is used to regenerate TPP.
d. Coenzyme A the carrier for the two carbons that enter the TCA cycle.
e. Coenzyme A reoxidizes lipoamide.
In part, the regulation of the enzyme pyruvate dehydrogenase is accomplished via post-translational modification (phosphorylation) via an enzyme called pyruvate dehydrogenase kinase. Under which condition listed below would you expect that pyruvate dehydrogenase would be phosphorylated?
a. High levels of NADH.
b. Low levels of ATP
c. High levels of ADP
d. High levels of Pyruvate
e. Low levels of acetyl-CoA
Explanation / Answer
1) Option D is the correct answer.
The statement, "Coenzyme A the carrier for the two carbons that enter the TCA cycle." best describes how coenzyme A is used. The citric acid cycle — also known as the tricarboxylic acid cycle (TCA cycle)is a series of enzyme-catalysed chemical reactions, which is of central importance in all living cells that use oxygen as part of cellular respiration. Most fuel molecules enter the cycle as acetyl coenzyme A.
2) Option A is the correct answer.
High Levels of NADH will stimulate pyruvate dehydrogenase kinase which will inactivate Pyruvate dehydrogenase by phosphorylation with ATP. The pyruvate dehydrogenase complex is regulated by covalent modification through the action of a specific kinase and phosphatase; the kinase and phosphatase are regulated by changes in NADH, acetyl-CoA, pyruvate, and insulin. PDH kinase is stimulated by NADH and acetyl-CoA. It is inhibited by pyruvate.
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