What types of interactions can occur between the side chains of the following amino acids that would help maintain the tertiary structure of a protein? a. cysteine and cysteine b. glutamine and serine c. glutamic acid and lysine d. proline and leucine

For each pair of amino acids given, we need to examine their side chains and determine which interactions might occur. a. Cysteine (Cys) has a side chain containing a sulfhydryl group (-SH). When two cysteine residues are in close proximity, they can form a covalent bond known as a disulfide bond (-S-S-). b. Glutamine (Gln) has a side chain with an amide group (-CONH₂), and Serine (Ser) has a side chain with a hydroxyl group (-OH). Both groups are polar and can participate in hydrogen bonding. c. Glutamic acid (Glu) has a side chain with a carboxyl group (-COOH), which can release a proton (H⁺) to become negatively charged (-COO⁻). Lysine (Lys) has a side chain with an amino group (-NH₂), which can accept a proton (H⁺) to become positively charged (-NH₃⁺). This means they can form a salt bridge (an ionic interaction between oppositely charged groups). d. Proline (Pro) has an unusually constrained cyclic side chain, and Leucine (Leu) has a hydrophobic nonpolar side chain. They can interact through hydrophobic interactions.

Now we can identify the types of interactions that can occur between the side chains of the given amino acid pairs: a. Cysteine and cysteine: Disulfide bond. b. Glutamine and serine: Hydrogen bond. c. Glutamic acid and lysine: Salt bridge. d. Proline and leucine: Hydrophobic interaction.