Which of the following would not be expected to diffuse thro

Which of the following would not be expected to diffuse through a lipid bilayer membrane?

a. tryptophan at pH 11

b. tryptophan at pH 11 with a methyl ester blocking the carboxyl group

Solution

Since the pH > pKa of Tryptophan, which means that the base form is more abundant than the acidic form, hence, Tryptophan at pH 11 will not be able to pass through the lipd bilayer membrane since positively charged tryptophan has more permeability through the lipid bilayer membrane.

If the carbboxyl group is blocked with a methyl ester then the positive charge prevails so the modified Tryptophan easily diffuses through the lipid bilayer.

hence the correct answer is a.