A strain of mice has been developed that lack the enzyme...

Name: Problem 14, Chapter 21: Biochemistry
Uploaded: 2021-01-22T01:50:36-08:00
Duration: 1 min 6 s
Channel: Prashant Bana
Description: A strain of mice has been developed that lack the enzyme phosphorylase kinase. Yet, after strenuous exercise, the glycogen stores of a mouse of this strain are depleted. Explain how this depletion is possible.

A strain of mice has been developed that lack the enzyme phosphorylase kinase. Yet, after strenuous exercise, the glycogen stores of a mouse of this strain are depleted. Explain how this depletion is possible.

Key Concepts

Glycogenolysis

Glycogenolysis is the metabolic pathway in which glycogen is broken down into glucose-1-phosphate, ultimately providing an important source of energy during periods of increased demand. This process is tightly regulated to ensure that energy is available when needed, such as during exercise, through several enzyme-mediated steps and regulatory signals.

Glycogen Phosphorylase

Glycogen phosphorylase is the key enzyme that catalyzes the first step in glycogenolysis by cleaving glycogen to produce glucose-1-phosphate. Its activity is regulated both by covalent modification (phosphorylation) and by allosteric interactions with various metabolites, allowing the enzyme to respond quickly to changes in energy requirements.

Phosphorylase Kinase

Phosphorylase kinase is an enzyme that normally activates glycogen phosphorylase by phosphorylating it, converting the less active form to a more active form during conditions such as stress or exercise. Although this enzyme plays a significant role in regulation, alternative mechanisms can compensate for its absence to ensure glycogen stores are utilized when needed.

Allosteric Regulation

Allosteric regulation involves the modulation of an enzyme's activity through the binding of effectors at sites other than the active site. In the context of glycogen metabolism, metabolites such as AMP can bind to glycogen phosphorylase, enhancing its activity even in the absence of phosphorylation by phosphorylase kinase. This allows the enzyme to adjust its activity in response to the energy status of the cell.

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