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Chapter 12: Problem 6

When the concentration of glucagon rises in the blood, which of the following enzyme activities is decreased? Explain. Adenylyl cyclase Protein kinase A PFK-2 (kinase activity) Fructose 1, 6-bisphosphatase

Short Answer

Expert verified
The activity of PFK-2 (kinase activity) likely decreases when the concentration of glucagon rises in the blood.

Step by step solution

01

Understand the role of glucagon

Glucagon is a hormone produced by the pancreas that works to prevent blood glucose levels from dropping too low. It does this by stimulating processes like glycogenolysis and gluconeogenesis, leading to the production of glucose and thus an increase in blood glucose concentrations. This basic contextual understanding helps in evaluating the impact on enzyme activities.
02

Evaluate each enzyme activity

Evaluate each enzyme one by one in the context of glucagon's role. Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP, and protein kinase A is an enzyme that is activated by cyclic AMP. When glucagon levels rise, it actually stimulates adenylyl cyclase and therefore Protein Kinase A as well. However, PFK-2, or Phosphofructokinase 2, and Fructose 1, 6-bisphosphatase operate on the opposite pathway that glucagon actives, meaning their activity would likely decrease when glucagon levels rise.
03

Identify the enzyme with decreased activity

Since adenylyl cyclase and protein kinase A are stimulated when glucagon levels rise, they are not the correct answer. Fructose 1, 6-bisphosphatase is an enzyme used in gluconeogenesis and would likely not decrease. However, PFK-2, or phosphofructokinase 2 (kinase activity), is used in glycolysis, an effect opposed by the actions of glucagon. Therefore, the activity of PFK-2 would logically decrease as glucagon concentrations increase.

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Most popular questions from this chapter

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?

(a) Draw the structures of the reactants and products for the second reaction catalyzed by transketolase in the pentose phosphate pathway. Show which carbons are transferred. (b) When \(2-\left[{ }^{14} \mathrm{C}\right]\)-glucose 6-phosphate enters the pathway, which atom of fructose 6-phosphate produced by the reaction in Part (a) is labeled? (c) When \(2-\left[{ }^{14} \mathrm{C}\right]\)-glucose 6-phosphate enters the pathway, which atom of fructose 6-phosphate produced by the transaldolase reaction is labeled?

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?

(a) How does the glucose-alanine cycle allow muscle pyruvate to be used for liver gluconeogenesis and subsequently returned to muscles as glucose? (b) Does the glucose-alanine cycle ultimately provide more energy for muscles than the Cori cycle does?

a) Is the energy required to synthesize glycogen from glucose 6-phosphate greater than the energy obtained when glycogen is degraded to glucose 6-phosphate? (b) During exercise, glycogen in both muscle and liver cells can be converted to glucose metabolites for ATP generation in the muscles. Do liver glycogen and muscle glycogen supply the same amount of ATP to the muscles?
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