16. A researcher wants to measure the binding affinity of estrogen to the estrogen receptor in a test tube. The concentration of the purified receptor is 10nM, while that of the ligand estrogen is 5nM. The KD value has been measured tobe 3nM. a) calculate the fractional saturation of estrogen receptor with estrogen under these conditions. b) calculate the free energy change upon binding under these conditions at 298K c) assuming an IC 50 of 15nM for progesterone, calculate the inhibition constant, Kl, of progesterone for inhibiting binding of estrogen to the estrogen receptor