Tryptophan*
–CH2
N
H
Trp
W
19 Histidine*
His
H
20 Proline
Pro
P
* essential amino acid, a = entire structure
Amino acids are classified as acidic, basic or neutral depending upon
the relative number of amino and carboxyl groups in their molecule Equal number of amino and carboxyl groups makes it neutral; more
number of amino than carboxyl groups makes it basic and more
carboxyl groups as compared to amino groups makes it acidic