Biochemistry, Vol. 1 - A. Lehninger 1985

Biomolecules
Water
Eight amino acids contain nonpolar R groups

The R groups of this Class of Amino Acids are Hydrocarbons and, consequently, they are hydrophobic (Fig. 5-6). This class includes Five amino acids with aliphatic R groups (Alanine, valine, leucine, isoleucine, and Proline), Two amino acids with aromatic rings (phenylalanine and Tryptophan), and one sulfur-containing amino acid (Methionine). Proline deserves special mention because its $\alpha$-amino group is not free, but substituted by part of the R group, resulting in a cyclic molecular Structure (Fig. 5-6).



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