Suppose a cell population has two kinds of receptors for a hormone. One receptor

Question

Suppose a cell population has two kinds of receptors for a hormone. One receptor has a Binding constant of 10^-6M, and causes the cell to release a yellow pigment. The other receptor has a binding constant of 10^-8M, and causes the cell to release ablue pigment. If you expose the cells to 10^-7M of the hormone, what color will the medium be? Assume that 50% of the hormone receptors must be bound for the cell to respond, and that when a cell responds, it always releases the same amount of pigment.
a. red
b. yellow
c. purple
d. blue
e. mostly yellow with about 1/4th blue.

Explanation / Answer

The binding constant for receptor 10-6 has high affinity for hormone . Hence the hormone binds instantly to the receptor 1 and the medium gets yellow colored.

Ka= [RH] / [R] [H]

ka for receptor 1 = [RH] / 10-6 *10-7 = [RH]/ 10-13

ka for receptor 2 = [RH] / 10-8 *10-7 = [RH]/ 10-15

From the above values it is clear that receptor 1 has greater affinity and when the receptor 1 gets filled half way or more the hormones attaches to the receptor 2.

hence after 50% filling of receptors the medium will be yellow.

Hence option b.

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