N-terminus
![A tetrapeptide (example: Val-Gly-Ser-Ala) with green highlighted N-terminal α-amino acid (example: L-valine) and blue marked C-terminal α-amino acid (example: L-alanine). This tetrapeptide could be encoded by the mRNA sequence 5'-GUUGGUAGUGCU-3'.](/Images/godic/202501/30/Tetrapeptide_structural_formulae_v.13345.png")
The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or amine-terminus) refers to the start of a protein or polypeptide terminated by an amino acid with a free amine group (-NH2). By convention, peptide sequences are written N-terminus to C-terminus, left to right in LTR languages. This correlates the translation direction to the text direction (because when a protein is translated from messenger RNA, it is created from N-terminus to C-terminus - amino acids are added to the carbonyl end).