Scientists examined the folded structure of a purified protein resuspended in water and found that amino acids with nonpolar R groups were primarily buried in the middle of the protein, whereas amino acids with polar R groups were primarily on the surface of the protein. Which of the following best explains the location of the amino acids in the folded protein?
a. Polar R groups on the surface of the protein can form ionic bonds with the charged ends of the water molecules.
b. Polar R groups are too bulky to fit in the middle of the protein and are pushed towards the protein's surface.
c. Nonpolar R groups that cannot form hydrogen bonds with water are pushed into the middle of the protein.
d. Nonpolar R groups from different parts of the protein form covalent bonds with each other to maintain the protein's structure.