Collagen contains an amino acid that is a modified form of the naturally occurring amino acid.

a. Name the natural amino acid.

Interactions of amino acids on the interior of proteins are key to the shapes of proteins. In group (a), which pairs of amino acids form hydrophobic interactions? In group (b), which pairs form ionic interactions? Which pairs in group (c) form hydrogen bonds?

a. 1 Pro . . . Phe

   2 Lys . . . Ser

   3 Thr . . . Leu

   4 Ala . . . Gly

What kind of bond would you expect between the side chains of the following amino acids?

c. Aspartic acid and asparagine

What kind of bond would you expect between the side chains of the following amino acids?

b. Alanine and leucine

For each amino acid listed, tell whether its influence on tertiary structure is largely through hydrophobic interactions, hydrogen bonding, formation of salt bridges, covalent bonding, or some combination of these effects.

a. Tyrosine

What type of R group interaction is the most likely between the alanine and isoleucine residues?

Oxytocin is a small peptide that is used to induce labor by causing contractions in uterine walls. It has the primary structure Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gln. This peptide is held in a cyclic configuration by a disulfide bridge. Draw a diagram of oxytocin, showing the disulfide bridge.

How do the following noncovalent interactions help to stabilize the tertiary and quaternary structure of a protein? Give an example of a pair of amino acids that could give rise to each interaction.

a. Hydrophobic interactions