Concept explainers
REFLECT AND APPLY Comment on the fact that the reduction of pyruvate to lactate, catalyzed by lactate dehydrogenase, is strongly exergonic (recall this from Chapter 15), even though the standard free-energy change for the half reaction
is positive
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Chapter 20 Solutions
Biochemistry
- REFLECT AND APPLY Suggest a reason why a different reducing agent (NADPH) is used in anabolic reactions rather than NADH, which plays a role in catabolic ones.arrow_forwardREFLECT AND APPLY Why does the degradation of palmitic acid (see Question 12) to eight molecules of acetyl-CoA require seven, rather than eight, rounds of the -oxidation process?arrow_forwardREFLECT AND APPLY The malate-aspartate shuttle yields about 2.5 moles of ATP for each mole of cytosolic NADH. Why does nature use the glycerol-phosphate shuttle, which yields only about 1.5 moles of ATP?arrow_forward
- REFLECT AND APPLY There is a reaction in carbohydrate meta- bolism in which glucose-6-phosphate reacts with NADP+ to give 6-phosphoglucono- -lactone and NADPH. In this reaction, which substance is oxidized, and which is reduced? Which substance is the oxidizing agent, and which is the reducing agent?arrow_forwardREFLECT AND APPLY Does the net gain of ATP in glycolysis differ when glycogen, rather than glucose, is the starting material? If so, what is the change?arrow_forwardREFLECT AND APPLY Why is it useful to plot rate data for enzymatic reactions as a straight line rather than as a curve?arrow_forward
- REFLECT AND APPLY Explain how glycogen phosphorylase is controlled allosterically and by covalent modification.arrow_forwardREFLECT AND APPLY What are some of the difficulties in determining the exact number of protons pumped across the inner mitochondrial membrane by the respiratory complexes?arrow_forwardREFLECT AND APPLY The following half reactions play important roles in metabolism. 1/2O2+2H++2eH2ONADH+H+NAD++2H++2e Which of these two is a half reaction of oxidation? Which one is a half reaction of reduction? Write the equation for the overall re- action. Which reagent is the oxidizing agent (electron acceptor)? Which reagent is the reducing agent (electron donor)?arrow_forward
- REFLECT AND APPLY Noncompetitive inhibition is a limiting case in which the effect of binding inhibitor has no effect on the affinity for the substrate and vice versa. Suggest what a LineweaverBurk plot would look like for an inhibitor that had a reaction scheme similar to that on page 159 (noncompetitive inhibition reaction), but where binding inhibitor lowered the affinity of EI for the substrate.arrow_forwardREFLECT AND APPLY How does an increase in the ADP/ATP ratio affect the activity of isocitrate dehydrogenase?arrow_forwardREFLECT AND APPLY Why is it reasonable to expect that glucose- 6-phosphate will be oxidized to a lactone (see Question 52) rather than to an open-chain compound?arrow_forward
- BiochemistryBiochemistryISBN:9781305961135Author:Mary K. Campbell, Shawn O. Farrell, Owen M. McDougalPublisher:Cengage Learning