18. Amino Acids and Proteins

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

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

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?

Identify the amino acids and type of interaction that occurs between the following R groups in tertiary protein structures: (16.1, 16.3)

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Identify the amino acids and type of interaction that occurs between the following R groups in tertiary protein structures: (16.1, 16.3)

c. —CH₂—SH and HS—CH₂—

What type of interaction would you expect between the following in a tertiary structure? (16.1, 16.3)

a. threonine and glutamine

 If glutamate were replaced by proline in a protein, how might the tertiary structure be affected? (16.1, 16.3)

Consider the amino acids histidine, phenylalanine, and serine in an enzyme. State which of these amino acids have R groups that would: (16.1, 16.3)

d. form salt bridges

What type of interaction would you expect between the R groups of the following amino acids in a tertiary structure?

c. serine and aspartate

In myoglobin, about one-half of the 153 amino acids have nonpolar R groups.

a. Where would you expect those amino acids to be located in the tertiary structure?

In myoglobin, about one-half of the 153 amino acids have nonpolar R groups.

b. Where would you expect the polar R groups to be in the tertiary structure?

When a protein folds into its tertiary structure, does the primary structure change? Explain.

What type of interaction would you expect between the side chains of each of the following pairs of amino acids in the tertiary structure of a protein?

b. alanine and valine

"What type of interaction would you expect between the side chains of each of the following pairs of amino acids in the tertiary structure of a protein?

a. lysine and glutamate"

What type of interaction would you expect between the side chains of each of the following pairs of amino acids in the tertiary structure of a protein?

b. leucine and isoleucine

What type of interaction would you expect between the side chains of each of the following pairs of amino acids in the tertiary structure of a protein?

d. glutamine and arginine

Myoglobin is a protein containing 153 amino acids. Approximately half of the amino acids in myoglobin have polar side chains.

a. Where would you expect these amino acid side chains to be located in the tertiary structure of the protein?

Myoglobin is a protein containing 153 amino acids. Approximately half of the amino acids in myoglobin have polar side chains.

b. Where would you expect the nonpolar side chains to be?

b. Would you expect to find this segment at the center or on the surface of a globular protein? Why?

Name the covalent bond that helps to stabilize the tertiary structure of a protein.

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

a. Name the natural amino acid.