5. (20 points) Receptor Signaling Suppose that the circulating concentration of

Question

5. (20 points) Receptor Signaling Suppose that the circulating concentration of dopamine in your bloodstream is 1010 M and the Ka for binding to the dopamine D2 receptor is 10s M. (a.) What fraction of Dz receptors in your cells will have dopamine bound? (b) If a meaningful physiological response occurs when 50% of the D2 receptors have bound a dopamine molecule, how much will the concentration of dopamine have to rise to elicit a response? (c) In reality, there are 5 different dopamine receptors in humans (D·Da D, D, and D and dopamine is known to bind to each of these receptors with a different affinity (Kd) Propose a reason why cells have evolved 5 different receptors to bind dopamine hint: s) hin buth iae careetor. (d.) Dopamine receptors are involved in chronic depression, and therefore pharmaceutical companies have synthesized "dopamine-like" drugs like Zyprexa to interact with these receptors and alter their signaling. Briefly explain the challenges associated with designing drugs to be both selective and potent, and how drugs give rise to side effects.

Explanation / Answer

a)Theta (fraction)= L/L+Kd

1x 10-10/10-8 = 1/100

B) here, Theta is 50%

0.5 = L/L + Kd

L = (L+Kd) 0.5= 0.5Kd/1-0.5 = (0.5)10-8/0.5= 10-8M

That is at 10-8 M the ligand will be bound 50% to the receptor

c) differences affinity of the receptor are responsible for initiating different responses in respective cells. This is why cells in different tissues respond differently to dopamine due to various responses initiated as the basis of their affinity tondopamine

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