Final answer:
Fully folded proteins typically have a polar side chain on their surfaces to interact with the surrounding environment and facilitate protein-protein interactions. The interior of the protein is made up of nonpolar amino acids to maintain the stability of the folded structure.
Step-by-step explanation:
Fully folded proteins typically have a polar side chain on their surfaces because it allows them to interact with the surrounding aqueous environment. The polar side chains contain hydrophilic amino acids that can form hydrogen bonds with water molecules, increasing the solubility of the protein.
These polar side chains on the surface also play a role in protein-protein interactions. They can form hydrogen bonds and electrostatic interactions with other molecules, facilitating binding and signaling processes.
However, the interior of the protein is made up of nonpolar amino acids with hydrophobic side chains. These hydrophobic amino acids are important for maintaining the stability of the protein's folded structure by forming hydrophobic interactions with each other.