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

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

Which of the following amino acid pairs are the most likely to form hydrogen bonds?

Which of the following amino acid pairs can form a salt bridge?

Both α-keratin and tropocollagen have helical secondary structure. How do these molecules differ in (a) amino acid composition and (b) three-dimensional structure?

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

Is the bond formed between each pair in Problem 18.76 covalent or noncovalent?

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