Replacing the hydroxyl group of a small organic molecule with a methyl group often changes how that molecule behaves in a cell. Which statement best explains this sensitivity?

Core Concept

Functional groups are the reactive sites of organic molecules. A hydroxyl group is polar and hydrogen bonds readily, so it raises solubility and provides a site for reactions such as ester formation. Replacing it with a nonpolar methyl group removes the electronegative oxygen, so the molecule loses a hydrogen-bonding site and gains hydrophobic character. Because cellular chemistry occurs mostly in aqueous solution, changes in polarity alter reactivity, membrane permeability, and binding to proteins. Small changes in functional groups therefore produce large differences in biological behavior.