Chapter 12: Problem 2
What important products of the citric acid cycle are required for gluconeogenesis from pyruvate?
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The pentose phosphate pathway and the glycolytic pathway are interdependent, since they have in common several metabolites whose concentrations affect the rates of enzymes in both pathways. Which metabolites are common to both pathways?
Individuals with a total deficiency of muscle glycogen phosphorylase (McArdle's disease) cannot exercise strenuously due to muscular cramping. Exertion in these patients leads to a much greater than normal increase in cellular ADP and \(\mathrm{P}_{\mathrm{i}}\). Furthermore, lactic acid does not accumulate in the muscles of these patients, as it does in normal individuals. Explain the chemical imbalances in McArdle’s disease.
The polypeptide hormone glucagon is released from the pancreas in response to low blood glucose levels. In liver cells, glucagon plays a major role in regulating the rates of the opposing glycolysis and gluconeogenesis pathways by influencing the concentrations of fructose 2,6 bisphosphate (F2,6 BP). If glucagon causes a decrease in the concentrations of F2,6 BP, how does this result in an increase in blood glucose levels?
Glycogen storage diseases (GSDs) due to specific enzyme deficiencies can affect the balance between glycogen stores and blood glucose. Given the following diseases, predict the effects of each on (1) the amount of liver glycogen stored and (2) blood glucose levels. (a) Von Gierke disease (GSD-1a), defective enzyme: glucose 6-phosphatase. (b) Cori's disease (GSD III), defective enzyme: amylo1,6 glucosidase (debranching enzyme). (c) Hers's disease (GSD VI), defective enzyme: liver phosphorylase
(a) In muscle cells, insulin stimulates a protein kinase that catalyzes phosphorylation of protein phosphatase-1, thereby activating it. How does this affect glycogen synthesis and degradation in muscle cells? (b) Why does glucagon selectively regulate enzymes in the liver but not in other tissues? (c) How does glucose regulate the synthesis and degradation of liver glycogen via protein phosphatase-1?
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