Classify each amino acid as polar, nonpolar, acidic, or basic.
a) Glu
b) Val
c) Pro
d) Lys
e) Gln
f) Arg 

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.

Provide one letter codes for amino acids with neutral hydrophilic R groups that participate in H bonding.

Valine is an amino acid with a nonpolar side chain and serine is one with a polar side chain. Draw the two amino acids.

a. Why is the side chain for valine nonpolar, whereas the side chain for serine is polar?

Which amino acid is hydrophilic (dissolves in aqueous solutions)? Why?

a. isoleucine

b. phenylalanine

c. aspartic acid

Cell membranes are studded with proteins. Some of these proteins, involved in the transport of molecules across the membrane into the cell, span the entire membrane and are called transmembrane proteins. The interior of the cell membrane is hydrophobic and nonpolar, whereas both the extracellular and intracellular fluids are water-based.

a. List three amino acids you would expect to find in the part of a transmembrane protein that lies within the cell membrane.