Download Aromatic Amino Acids

Aromatic Amino Acids
Aromatic amino acids are relatively nonpolar. To different degrees, all aromatic amino acids absorb ultraviolet
light. Tyrosine and tryptophan absorb more than do phenylalanine; tryptophan is responsible for most of the
absorbance of ultraviolet light (ca. 280 nm) by proteins. Tyrosine is the only one of the aromatic amino acids with
an ionizable side chain. Tyrosine is one of three hydroxyl containing amino acids.
Least hydrophobic
Very hydrophobic
Aliphatic Amino Acids
Aliphatic R groups are nonpolar and hydrophobic. Hydrophobicity increases with increasing number of C atoms in the hydrocarbon
chain. Although these amino acids prefer to remain inside protein molecules, alanine and glycine are ambivalent, meaning that they can be
inside or outside the protein molecule. Glycine has such a small side chain that it does not have much effect on the hydrophobic
interactions.
The structures below are shown in the ionization state that predominates at pH 7.
Less hydrophobic
More hydrophobic