Table 1. Five categories of 20 amino acids.

Category	Amino Acids a
Amino Acids with Positive Charged Side Chains	R, H, K
Amino Acids with Negative Charged Side Chains	D, E
Amino Acids with Polar Uncharged Side Chains	S, T, N, Q
Amino Acids with Hydrophobic Side Chains	A, I, L, M, F, W, Y, V
Special Cases	C, G, P

^a Standard abbreviations are used for all amino acids.