Practice Problem 1

Use the structures of the following amino acids in the table of standard amino acids to classify these compounds as either nonpolar/hydrophobic, polar/hydrophilic, negatively charged/hydrophilic, or positively charged/hydrophilic.

(a) Valine: R = -CH(CH₃)₂

(b) Serine: R = -CH₂OH

(c) Aspartic acid: R = -CH₂CO₂^-

(d) Lysine: R = -(CH₂)₄NH₃⁺

Solution

(a) Valine is a nonpolar, hydrophobic amino acid.

(b) Serine is a polar, hydrophilic amino acid.

(c) Aspartic acid is a hydrophilic amino acid with a negatively charged R group.

(d) Lysine is a hydrophilic amino acid with a positively charged R group.