Many proteins are soluble in water, yet they contain amino acid R groups that are hydrocarbon-like. For example, look at the structures of leucine (leu), isoleucine (ile), valine (val), or phenylalanine (phe). What is the likely explanation for how this is possible?
a. The hydrocarbon-like parts of the molecule become water-soluble when they are attached to the amide part of the amino acid residue.
b. Proteins fold up so that the hydrocarbon parts are inside surrounded by parts of the protein that contain more water soluble hydrogen bonding groups on the outside (much like the way soaps and dispersants work).
c. Water soluble proteins do not contain amino acids with hydrocarbon R-groups.
d. The hydrocarbon chains on these amino acid R-groups aren't long enough to make them not soluble in water.