2 Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase the enzyme that breaks down glycogen to release glucose as depicted in the figure below A Provide a step by step explanation of the signaling pathway that communicates the extracellular signal into the cell and eventually triggers glycogen adrenergic receptor breakdown activated GPCR You do not need to write complete sentences Bullet points are encouraged B Identify all the steps in this pathway where the signal is amplified C Based on the signaling pathway shown on the previous page indicate whether the following statements are true or false Explain why the false statements are incorrect adrenaline Wil 1 A mutant form of the G protein a subunit that cannot bind GTP will increase the activation of PKA inactive phosphorylase kinase 2 A mutant form of GPCR that is always active in skeletal muscle cells would increase the amount of phosphorylated glycogen phosphorylase activated adenylyl cyclase inactive PKA ATP CAMP 10 ADP activated a subunit of stimulatory G protein G active PKA inactive glycogen phosphorylase GTP P ATP cyclic AMP ATP ADP active CYTOSOL phosphorylase kinase active glycogen phosphorylase GLYCOGEN BREAKDOWN 3 A mutant form of PKA that is always active in skeletal muscle cells would lead to a decrease in the amount of glucose available 4 A Compound B is a molecule with a very high affinity for cyclic AMP it binds tightly to any cyclic AMP available in the cell preventing it from interacting with other substrates Addition of Compound B to skeletal muscle cells leads to an excess in the amount of glycogen available