Question

Assume that the binding of one molecule of epinephrine to a seven‑transmembrane helix (7TM) receptor (also called the G protein‑coupled receptor, or GPCR) results in the activation of 360 Gα360 Gα subunits. In addition, suppose that each activated adenylyl cyclase catalyzes the conversion of 30 ATP30 ATP molecules to cAMP per second. Assume that each G protein activates a single unique adenylyl cyclase.

Calculate the number of moles of cAMP that are produced per second. Enter your answer to two significant figures.

Answer 1

Number of activated adenylyl cyclases = Number of G_alpha subunits released = 360

Number of cAMP molecules produced per second =

Number of ATP to cAMP reactions catalyzed by adenylyl cyclase x Number of activated adenylyl cyclases

= 30 x 360 = 1080 molecules per second

Molar mass of cAMP = 329.2  hence one mole of cAMP = 329.2 grams

One mole of cAMP contains N₀ molecules (N₀ = Avogadro's number = 6.022 x 10²²)

So 6.022 x 10²² molecules of cAMP = One mole of cAMP

Hence 1080 molecules of cAMP = 1080 / (6.022 x 10²²) = 1.79 x 10^-20 moles of cAMP

Therefore number of moles of cAMP produced per second = 1.79 x 10^-20 moles per second