Explanation

Amino acids have a central four valence carbon atom, called the alpha $(\alpha)$ carbon to which are attached (i) an amino group $( - NH_{2})$ on one side, (ii) a carboxyl groups $( - COOH)$ on the other side, (iii) a hydrogen atom (H) on the third side and (iv) a variable group symbolised by $R$ on the fourth side. Out of them, $NH_{2}$ and COOH are involved in peptide bond formation