What's the difference between i.e. and e.g.?
phenylalanine phen·yl·al·a·nine (fěn'əl-āl'ə-nēn', fē'nəl-)
An essential amino acid that occurs as a constituent of many proteins and is normally converted to tyrosine in the body.
An essential amino acid. Chemical formula: C9H11NO2. See more at amino acid.