Multiple Choice
What could be the result of a mutation in the R subunits of cAMP-dependent protein kinase A (PKA) that inhibits formation of the R2C2 protein complex?
12. Biosignaling
cAMP & PKA
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The image below is a schematic representation of PKA activation from epinephrine binding. Based on the provided numbers in the diagram, how many subunits of catalytically active PKA will there be?
A
1,000 molecules.
B
200 molecules.
C
100 molecules.
D
50 molecules.
E
400 molecules.
Verified step by step guidance1
Identify the initial step in the pathway: Epinephrine binds to its receptor, forming an epinephrine-receptor complex. According to the diagram, this involves 1 molecule of epinephrine.
Observe the next step: The epinephrine-receptor complex activates the Gs protein, which is shown to involve 10 molecules in the diagram.
Note the subsequent step: The activated Gs protein stimulates adenylyl cyclase, which converts ATP to cyclic AMP (cAMP). The diagram indicates that this results in the production of 200 molecules of cAMP.
Understand the role of cAMP: cAMP acts as a secondary messenger that activates Protein Kinase A (PKA). Each PKA is composed of two regulatory and two catalytic subunits. cAMP binds to the regulatory subunits, releasing the catalytic subunits.
Calculate the number of active PKA subunits: Since each PKA molecule requires 4 cAMP molecules to become fully active, divide the total number of cAMP molecules (200) by 4 to determine the number of catalytically active PKA subunits.
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