Question

Compare and contrast glycogen metabolism in the liver during fasting to glycogen metabolism in the skeletal muscle during exercise. What is unique about muscle glycogen metabolism

Answer 1

Answer: Glycogen regulation takes place in both liver and skeletal muscle cells as the glycogen is stored here in significant amount.

In glycogen synthesis the most important regulatory enzyme is Glycogen Synthase wheres Glygogen Phosphorylase is glycogen degradation enzyme.

In the liver cells the positive allosteric modulator is glucose 6 phosphate whereas glycogen phosphorylase negative modulator are glucose 6 phosphate, ATP and glucose.

In the skeletal muscle cells the glycogen phosphorylase is negatively regulated glucose 6 phosphate, ATP and glucose in liver where as in skeletal muscle cell it is only glucose 6 phosphate and ATP(no glucose) which are negative modulator.

In skeletal muscle cell AMP is acting as positive modulator of glycogen phosphorylase.

All other regulation process is same for both liver and skeletal muscle cell but the uniqueness of skeletal muscle is that the glucagon do not act on skeletal muscle simply because glucagon skeletal muscle cell do not have glucagon receptors.