Assume that the binding of one molecule of epinephrine to a seven-transmembrane

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 260 G_a subunits. In addition, suppose that each activated adenylyl cyclase catalyzes the conversion of 20 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 at least two significant figures. Note that these numbers are used for illustrative purposes only. The actual rates are different (and laraer), and vary depending on type of receptor and regulatory proteins that increase or decrease the rate of the GTPase activity of the subunit.

Explanation / Answer

Given that each Ga subunit activates one unit of adenyl cyclase,

No. of cAMP molecules produced per second = 30 * 420 = 12600 molecules/s

No. of moles per second = 12600/(6.022 * 1023) = 2092.32 * 10-23 mol/s = 2.1 * 10-20 mol/s

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