Many plasma proteins found in an aqueous environment are globular in shape. Which amino acid side chains would you expect to find on the surface of a globular protein and in contact with the aqueous environment? Which would you expect to find inside, shielded from the aqueous environment? Explain. (a) Leu (b) Arg (c) Ser (d) Lys (e) Phe

Hydrophobic amino acids have non-polar side chains, which means they do not interact well with water. They tend to be found in the interior of globular proteins to minimize their contact with water. Hydrophilic amino acids have polar or charged side chains, allowing them to form favorable interactions (like hydrogen bonds) with water. These amino acids usually reside on the surface of globular proteins, exposed to the aqueous environment.

Based on the given amino acids, we can classify them as follows: (a) Leu (Leucine) - Hydrophobic, non-polar aliphatic side chain (b) Arg (Arginine) - Hydrophilic, positively charged side chain (c) Ser (Serine) - Hydrophilic, polar side chain with a hydroxyl group (d) Lys (Lysine) - Hydrophilic, positively charged side chain (e) Phe (Phenylalanine) - Hydrophobic, aromatic side chain

Based on the properties of each amino acid, we can now determine their location in a globular protein. (a) Leu: Inside the protein, shielded from the aqueous environment (hydrophobic) (b) Arg: On the surface of the protein, in contact with the aqueous environment (hydrophilic) (c) Ser: On the surface of the protein, in contact with the aqueous environment (hydrophilic) (d) Lys: On the surface of the protein, in contact with the aqueous environment (hydrophilic) (e) Phe: Inside the protein, shielded from the aqueous environment (hydrophobic) So, we can expect amino acids with hydrophilic side chains (Arg, Ser, and Lys) to be on the surface of a globular protein and in contact with water, while amino acids with hydrophobic side chains (Leu and Phe) will be found inside the protein, shielded from the aqueous environment.