Final answer:
In muscle cells lacking adenylyl cyclase, glycogen levels would be higher in the presence of adrenaline, as the signaling pathway for glycogen breakdown and inhibition of synthesis cannot be activated.
Step-by-step explanation:
When adrenaline, also known as epinephrine, binds to its receptor on muscle cells, a series of events is triggered that leads to the breakdown of glycogen into glucose. Adenylyl cyclase is an enzyme that converts ATP to cyclic AMP (cAMP). cAMP acts as a second messenger, activating protein kinase A (PKA), which then phosphorylates enzymes related to glycogen metabolism. The activation of glycogen phosphorylase leads to glycogenolysis, breaking down glycogen into glucose, while the phosphorylation of glycogen synthase inhibits glycogenesis, preventing the formation of new glycogen.
In muscle cells lacking adenylyl cyclase, this cascade cannot happen because the cAMP levels required to activate PKA and hence glycogen phosphorylase and inhibit glycogen synthase cannot be raised. Therefore, in the presence of adrenaline, glycogen levels in muscle cells that lack adenylyl cyclase would be higher, as breakdown is impaired and synthesis continues as normal.