The end of a polypeptide chain with the unattached amino group (-NH2 group). Each amino acid in the chain has an amino group on one side (which is attached to the carboxyl group (a -COOH group) of the previous amino acid) and a carboxyl group on the other side (which is attached to the amino group of the next amino acid). The other end of the polypeptide chain is called the carboxyl terminal.