18. Amino Acids and Proteins

Give the three-letter and one-letter abbreviations and identify the functional group in the side chain for each amino acid in Problem 10.1.

a. alanine

b. lysine

c. tryptophan

d. aspartate

Draw the structure for each of the following amino acids and put an asterisk (*) next to any chiral carbon centers in your structure:

c. methionine

Classify each amino acid in Problem 10.4 as polar (neutral, acidic, or basic) or nonpolar and as hydrophobic or hydrophilic.

a. leucine

b. glutamate

c. methionine

d. threonine

Isoleucine has the zwitterion structure shown. Draw the structure and give the net charge of isoleucine that will predominate at the indicated pH values (pI = 6.0).

b. pH 6.0

Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).

b. pH 12.0

Consult Table 18.3 and draw alanine. Label the functional groups and give the three-letter abbreviation and the one-letter abbreviation. What group does the side chain fall into?

Draw the structure of glutamic acid at low pH, at high pH, and at the two forms that exist between low pH and high pH. Which of these structures represents the zwitterion?

Name and draw the structures of the amino acids that fit the following descriptions:

a. Contains an isopropyl group

Name and draw the structures of the amino acids that fit the following descriptions:

a. Contains a thiol group

At neutral pH, which of the following amino acids has a net positive charge, which has a net negative charge, and which is neutral? (Hint: Draw the various charged forms of each amino acid before deciding.)

a. Asparagine

b. Lysine

c. Proline

Which of the following forms of aspartic acid would you expect to predominate at low pH, neutral pH, and high pH?

a.

b.

c.

Which form of aspartic acid in Problem 18.54 is the zwitterion? What is the pI for the zwitterion?

a.

b.

c.