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The Citric Acid Cycle

Problems

The Reactions of the Citric Acid Cycle

How to Cite This SparkNote

Problem : What is the name of the enzyme that catalyzes the reaction that joins a molecule of acetyl-CoA and oxaloacetate?

Citrate synthase.

Problem : From which position on citrate to which position is the –OH group transferred in the second step of the citric acid cycle by the enzyme acontinase?

Citrate has an –OH group on its 3' carbon. The enzyme acontinase moves the –OH to the 4' position.

Problem : What two types of reactions are catalyzed by the enzyme isocitrate dehydrogenase in the third reaction of the citric acid cycle?

The first reaction is an oxidation and the second is a loss of carbon dioxide, or a decarboxylation.

Problem : In which of the first five steps of the citric acid cycle is NADH produced?

NADH is produced in the third and fourth reactions of the citric acid cycle by the enzymes isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Problem : What citric acid cycle enzyme is responsible for catalyzing the reaction that produces GTP?

Succinyl-CoA synthetase.

Problem : Fill in the blanks with the appropriate choice. FAD is the __________ (oxidized/reduced) form of flavin adenine dinucleotide while FADH is the __________ (oxidized/reduced) form.

Oxidized. Reduced.

Problem : What is the product when succinate is oxidized by the removal of two hydrogens by the enzyme succinate dehydrogenase?

Fumarate.

Problem : Which molecule, NAD or FAD, would likely oxidize the following molecule?

Figure %: Oxidation of an alcohol to an aldehyde.

Because methanol contains a carbon-oxygen bond, NAD would likely oxidize it. FAD usually oxidizes carbon-carbon bonds.

Problem : Name the enzyme that converts fumarate to L-malate.

Fumarase.

Problem : Name the "final product" of the citric acid cycle. Why is this product not really the final product?

Oxaloacetate is the product of the final enzymatic reaction of the citric acid cycle. It is not really the final product because it is used over again in first reaction of the cycle with acetyl-CoA. In this way, it is also a starting material in the cycle.

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