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 240 Ga 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 Number mol cAMP/s Note that these numbers are used for illustrative purposes only. The actual rates are different (and larger) and vary depending on type of receptor and regulatory proteins that increase or decrease the rate of the GTPase activity of the Ga subunit. Previous ? Give Up & View Solution Check Answer 0 Next Exit

Explanation / Answer

ans)

As stated in the question:

No. of activated G? subunits= 240

Each molecule of activated G? subunits activates single adenylyl cyclase.

Therefore, total no. of adenylyl cyclase activated by G? subunits =240

One activated adenylyl cyclase catalyses the conversion of 20 ATP molecules to cAMP per second. This implies, 1 molecule of adenylyl cyclase produces 20 molecules of cAMP are per second.

Therefore, 240 molecules activated adenylyl cyclase will produce 240*20 =4800 molecules of cAMP. One mole of cAMP contains 6*1023 molecules of cAMP. Therefore, 4800 cAMP molecules are equivalent to

4800/6*1023 = 8 *10-21 moles. or 0.8*10^-20 moles

Hence, 8*10-21 moles of cAMP are produced per second.

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