Uark Biochem Chapter 19: The Citric Acid Cycle: Exam 3

Key control points in the citric acid cycle

• The reactions catalyzed by isocitrate dehydrogenase and a-ketoglutarate dehydrogenase

Step 1

Reactants: Acetyl CoA, Oxaloacetate, and H2O

Products: Citrate, CoA, and H+

Enzyme: Citrate synthase

Step 2

Reactants: Citrate

Product: Isocitrate

Enzyme: Aconitase

Step 3

Reactant: Isocitrate and NAD+

Product: a-ketoglutarate, CO2, NADH

Enzyme: Isocitrate dehydrogenase

Step 4

Reactant: a-ketoglutarate, NAD+, CoA

Product: Succinyl CoA, CO2, NADH

Enzyme: a-ketoglutarate dehydrogenase complex

Step 5

Reactant: Succinyl CoA, Pi, ADP

Product: Succinate, ATP, CoA

Enzyme: Succinyl CoA sythetase

Step 6

Reactants: Succinate and FAD

Products: Fumarate and FADH2

Enzyme: Succinate dehydrogenase

Step 7

Reactant: Fumarate and H2O

Product: L-malate

Enzyme: Fumarase

Step 8

Reactant: L-malate and NAD+

Product: Oxaloacetate, NADH, H+

Enzyme: Malate dehydrogenase

Citric Acid Cycle Net Reaction

What is not a component of the citric acid cycle?

Propionyl CoA

The complete oxidation of one molecule of acetyl CoA by the citric acid cycle results in…

Generation of two molecules of CO2

Pyrivate dehydrogenase complex

Converts pyruvate into acetyl CoA

Citrate synthase

Condenses oxaloacetate and acetyl CoA

Aconitase

Catalyzes the formation of isocitrate

Isocitrate dehydrogenase

Catalyzes the formation of a-ketoglutarate

a-ketoglutarate dehydrogenase

Synthesizes succinyl CoA

Succinyl CoA synthetase

Generates ATP

Succinate dehydrogenase

Synthesizes fumarate

Fumarase

Generates malate

Malate dehydrogenase

Catalyzes the formation of oxaloacetate

Pyruvate carboxylase

Converts pyrivate into oxaloacetate

What reaction in the citric acid cycle results in the direct formation of a molecule of ATP?

• The reaction catalyzed by succinyl CoA synthetase

  • Succinyl CoA + Pi + ADP → Succinate + CoA + ATP

Which enzymes are the key regulatory enzymes of the citric acid cycle itself?

Isocitrate dehydrogenase and a-ketoglutarate dehydrogenase