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Identify the two steps in glycolysis in which ATP is produced.

Write mechanisms for step 2 of the citric acid cycle, the dehydration of citrate and the addition of water to \(c i s\) -aconitate.

Write a mechanism for step 6 of gluconeogenesis, the reduction of 1,3 -bisphosphoglycerate with \(\mathrm{NADH} / \mathrm{H}^{+}\) to yield glyceraldehyde 3 -phosphate.

What coenzyme is typically associated with each of the following transformations? (a) The phosphorylation of an alcohol to give a phosphate (b) The oxidative decarboxylation of an \(\alpha\) -keto acid to give a thioester (c) The carboxylation of a ketone to give a \(\beta\) -keto acid

Lactate, a product of glucose catabolism in oxygen-starved muscles, can be converted into pyruvate by oxidation. What coenzyme do you think is needed? Write the equation in the usual biochemical format using a curved arrow.

Plants, but not animals, are able to synthesize glucose from acetyl CoA by a pathway that begins with the glyoxalate cycle. One of the steps in the cycle is the conversion of isocitrate to glyoxalate plus succinate, a process catalyzed by isocitrate lyase. Propose a mechanism for the reaction.

Propose a mechanism for the conversion of 6-phosphogluconate to 2-keto-3-deoxy-6-phosphogluconate, a step in the Entner-Douderoff bacterial pathway for glucose catabolism.

Galactose, one of the eight essential monosaccharides (Section \(21-7\) ), is biosynthesized from UDP-glucose by galactose 4 -epimerase, where UDP \(=\) uridylyl diphosphate. The enzyme requires \(\mathrm{NAD}^{+}\) for activity, but it is not a stoichiometric reactant and NADH is not a final reaction product. Propose a mechanism.

L-Fucose, one of the eight essential monosaccharides (Section \(21-7\) ), is biosynthesized from GDP-D-mannose by the following three-step reaction sequence: (a) Step 1 involves an oxidation, a dehydration, and a reduction. The step requires NADP \(^{+}\), but no NADPH is formed as a final reaction product. Propose a mechanism. (b) Step 2 accomplishes two epimerizations and utilizes acidic and basic sites in the enzyme but does not require a coenzyme. Propose a mechanism. (c) Step 3 requires NADPH as coenzyme. Show the mechanism.