Chapter 14

What are the chemical and functional differences between NADH and NADPH?

What are the three metabolic conditions that determine metabolic flux through the pentose phosphate pathway?

What is the primary mechanism by which metabolic flux is regulated in the pentose phosphate pathway?

Why are reduced glutathione levels in red blood cells dependent on the activity of the enzyme glucose-6-phosphate dehydrogenase? Why are individuals with a glucose-6-phosphate dehydrogenase deficiency sensitive to prophylactic antimalarials such as primaquine, but at the same time more resistant to developing malaria even without primaquine treatment?

The conversion of pyruvate to phosphoenolpyruvate in the gluconeogenic pathway requires phosphoryl transfer energy in reactions catalyzed by the enzymes pyruvate carboxylase (ATP dependent) and phosphoenolpyruvate carboxykinase (GTP dependent). Why is this pair of reactions counted as a cost of 4 ATP equivalents to convert pyruvate to phosphoenolpyruvate when counting up the number of ATP needed to generate one molecule of glucose?

Pyruvate carboxylase is often considered a gluconeogenic enzyme; however, it also plays an important role in an energy-converting pathway under conditions of low energy charge and high acetyl-CoA levels in mitochondria. What is the name of this pathway?

What is the metabolic logic of reciprocal regulation of the glycolytic and gluconeogenic pathways by citrate?

Is phosphofructokinase-2/fructose-2,6-bisphosphatase one protein with two catalytic activities or two protein subunits each encoding a single catalytic activity? What regulates the two catalytic activities of phosphofructokinase-2/fructose-2,6-bisphosphatase?

Explain why the Cori cycle has a net cost of \(4 \mathrm{ATP}\) equivalents per glucose to the organism.

Glycogen contains an \(\alpha-1,6\) -glycosidic bond about once every 10 glucose residues, thereby creating a branch point and a corresponding non reducing end for the removal and addition of glucose molecules. If a glycogen particle contains a total of 50,000 glucose residues, how many nonreducing ends are most likely to be found: \(\sim 25,000\) ends, \(\sim 2,500\) ends, or \(\sim 250\) ends? Explain your answer.

The \(\Delta G^{\circ \prime}\) of the glycogen phosphorylase reaction is \(+3.1 \mathrm{kJ} / \mathrm{mol},\) whereas the \(\Delta G\) under physiologic conditions is \(-6 \mathrm{kJ} / \mathrm{mol} .\) What is likely to account for this difference of \(\sim 9 \mathrm{kJ} / \mathrm{mol}\) between the \(\Delta G^{\circ \prime}\) and \(\Delta G\) values?

What is the function of glucosc-6-phosphatasc in liver and muscle cells?

The product of the glycogen phosphorylase reaction is glucose-1-P. Is there a difference in glycolytic ATP yield comparing the yield from the metabolism of glucose-1-P derived from glycogen degradation with the yield from the metabolism of dietary glucose? Explain.

Explain the metabolic logic of glucagon and insulin regulation of glycogen metabolism.

Defects in essentially every enzyme required for human glycogen metabolism have been identified and are collectively called glycogen storage diseases. Explain why Andersen disease, caused by a defect in glycogen branching enzyme, is fatal, whereas Cori disease, caused by a defect in glycogen debranching enzyme, only manifests in mild hypoglycemia.