chapter 19 Citric Acid Cycle

Flashcards about the Citric Acid Cycle.

What is the primary catabolic purpose of the citric acid cycle?

To harvest high-energy electrons from carbon fuels.

What is oxidized in the citric acid cycle?

The acetyl fragment of acetyl CoA.

What are the products of the citric acid cycle?

CO2, NADH, FADH2, and ATP.

What two molecules combine to initiate the citric acid cycle?

Acetyl CoA and oxaloacetate.

What enzyme catalyzes the first step of the citric acid cycle?

Citrate synthase.

What six-carbon compound is formed in the first step of the citric acid cycle?

Citrate.

What is regenerated in the second stage of the citric acid cycle?

Oxaloacetate.

What is the role of high-energy electrons generated in the citric acid cycle?

To power the synthesis of ATP in oxidative phosphorylation.

What reaction is catalyzed by citrate synthase?

The condensation of acetyl CoA and oxaloacetate to form citrate.

What is the function of the enzyme aconitase?

Catalyzes the formation of isocitrate from citrate.

What products are created by Isocitrate dehydrogenase?

α-ketoglutarate and NADH.

What enzyme catalyzes the synthesis of succinyl CoA from α-ketoglutarate?

α-Ketoglutarate dehydrogenase complex

What high-energy molecule is formed from Succinyl CoA?

ATP

What kind of phosphorylation is the formation of ATP by succinyl coenzyme A synthetase?

Substrate-level phosphorylation.

What series of enzymes regenerate oxaloacetate?

Succinate dehydrogenase, fumarase, and malate dehydrogenase.

What are the products in the regeneration of oxaloacetate?

FADH2 and NADH

How many ATP are synthesized from electrons from NADH?

2.5

How many ATP are synthesized from electrons from FADH2?

1.5

What are the key control points in the citric acid cycle?

Reactions catalyzed by isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.

What is the role of citrate in biosynthesis?

Synthesis of fatty acids and sterols.

What is the role of α-ketoglutarate biosynthesis?

Synthesis of amino acids like glutamate.

What is the role of succinyl-CoA biosynthesis?

Synthesis of porphyrins used in hemoglobin.

What are reactions to replenish components of the citric acid cycle called?

Anaplerotic reactions.

What enzyme synthesizes oxaloacetate by carboxylation of pyruvate?

Pyruvate carboxylase.

What activates pyruvate carboxylase?

Acetyl CoA.

What is the role of pyruvate carboxylase?

Conversion of pyruvate to oxaloacetate, a crucial step in gluconeogenesis.

How does the glyoxylate cycle enable plants and bacteria to convert fats into carbohydrates?

It bypasses the two decarboxylation steps.

What is the product of the glyoxylate cycle?

Succinate

Animals lack what two enzymes necessary for the glyoxylate pathway?

Isocitrate lyase and malate synthase.

What does isocitrate lyase catalyze?

The conversion of isocitrate into succinate and glyoxylate.

Problem: Fluoroacetate inhibits the citric acid cycle. What step is inhibited?

The aconitase reaction.

What is a suicide substrate?

A compound that is not toxic per se, but is metabolically activated to a toxic product.

What is induced fit in enzymes?

A change in enzyme structure on substrate binding.

What two carbon atoms are oxidized in stage one of the citric acid cycle?

Two carbon atoms are oxidized to generate two molecules of CO2

What kind of structural changes does oxaloacetate binding cause?

Structural changes that lead to the formation of the acetyl CoA binding site.

What effect would fluorocitrate have on the reactions following the aconitase-catalyzed step?

All reactions would continue with the isocitrate formed before the introduction of fluoroacetate. No new isocitrate could be generated.

What process generates a proton gradient?

The reduction of O2.

What is the fate of oxaloacetate?

It would react with fluoroacetyl CoA until all citric acid cycle components were converted into fluorocitrate.

What molecule is a competitive inhibitor of succinate dehydrogenase?

Malonate

What enzyme catalyzes the conversion of malate to oxaloacetate?

Malate dehydrogenase