Since all 20 amino acids have a a carboxylic acid group and an amino group, biochemists refer to amino end of a polypeptide sequence as the “N-terminal”, whereas the Carboxyl group is referred to as the “C-terminal”.
Suppose alanine (above) joins with gylcine. The amino group of gylcine would attach to the carboxyl group after a condensation reaction occurs forming a dipeptide.
The amino group of alanine would be referred to as the N-terminus. The carboxyl group would be referred to as the C-terminus.
Note: All amino acid sequences are read from N-terminus to C-terminus.