adrenaline 1. You discover a signal transduction pathway that regulates glycogen
ID: 133678 • Letter: A
Question
adrenaline 1. You discover a signal transduction pathway that regulates glycogen breakdown. Adrenaline is the ligand, which binds to and activates a G-protein coupled receptor. Activation of this receptor leads to the activation of adenylyl cyclase that utilizes ATP to produce cyclic AMP (CAMP). CAMP activates PKA which then phosphorylates the phosphorylase kinase. Phosphorylase kinase phosphorylates glycogen phosphorylase which stimulates glycogen breakdown. This signal transduction pathway is diagramed in the figure CYTOSOL adenylyl cyclase PKA eyclic AMP CAMP phosphorylase ATP ADP glycogen For each of the situations below, indicatekinase whether you predict glycogen breakdown will increase, decrease, or stay the same compared to normal cells that are grown in the presence of adrenaline. (18 points total; 3 points each) ATP ADP glycogen phosphorylase GLYCOGEN BREAKDOWN a. The adrenaline binding site no longer binds adrenaline b. Constitutively active PKA instead of normal PKA. c. T765 on glycogen phosphorylase is changed to A765 which can't be phosphorylated. Dacyease d. The alpha subunit of the G-protein can no longer exchange or hydrolyze GTP into e. Phosphorylase kinase can no longer utilize ATP. (hint: think of what kinases utilize f. Constitutively active glycogen phosphorylase instead of normal glycogern GDP (hint: think of what it means for the G-protein to now always be GTP bound) ATP for) phosphorylase.Explanation / Answer
A) When adrenaline binding site no longer binds adrenaline, the entire downstream mechanism gets blocked and therefore glycogen breakdown decreases.
B) When the PKA is constitutively active, glycogen breakdown increases.
C) When glycogen phosphorylase can't be phosphorylated, glycogen breakdown doesn't occur. So, glycogen breakdown decreases.
D) When GTP cannot be hydrolysed to GDP, cyclic AMP cannot be formed. So, glycogen breakdown decreases.
E) Phosphorylase kinase phosphorylates glycogen phosphorylase. So, glycogen breakdown decreases.
F) When glycogen phosphorylase is constitutively active, glycogen breakdown increases.
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