The binding of epinephrine to the adrenergic receptor on skeletal muscle cells l

Question

The binding of epinephrine to the adrenergic receptor on skeletal muscle cells leads to the breakdown of glycogen leading to lower amounts of glycogen in the cell. Given what you know about this signaling pathway, explain what would happen if skeletal muscle cells were treated with epinephrine and had the following defects. In other words, would the glycogen levels be higher or lower than in normal cells treated with adrenaline? Remember to explain your answers.

a. Cells that had a defective adenylyl cyclase

b. Cells that had a defective G protein-coupled receptor

c. Cells that had a defective cAMP phosphodiesterase

d. Cells that had a phosphorylase kinase that could not be phosphorylated

Explanation / Answer

Cells treated with adrenaline usually have lower glucose levels than normal cells because adrenaline promotes cells to release and utilise glucose as energy source.

A.Cells with defective Adenyl cyclase will not be able to convert ATP into cAMP and pyrophosphate which in turn will make CAMP binding proteins inactive due to lack of regulatory signal in the form of CAMP.

B. Cells that have defective Gprotein coupled receptor will not be able to to receive signals from the their external environment and activate inside signal transduction pathway.

C.phosphodiestrase is an enzyme that breaks phosphodiester bond in the second messenger molecule CAMP and GMP and regulates second messenger pathway within the cell. Inactive form of this enzyme will interrupt in the localization, duration and signalling within the subcellular domains.

D. Phosphorylase kinase is a protein kinase which activates glycogen phosphorylase which releases glucose 1 phosphate from glycogen. The protein is made of 4 subunits alpha beta gamma and epsilon. Gamma subunit has catalytic activity while as other three subunits have regulatory function. alpha and beta subunits reduce the catalytic activity of enzyme but phosphorylation of these two of units reduce their inhibitory activities and activates the enzyme. Thus unphosphorylated phosphorylase kinase will remain inactive.

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