Define the following terms related to proteins: $(i)$ Peptide linkage,$(ii)$ Primary structure,$(iii)$ Denaturation.

(N/A) $(i)$ Peptide linkage: The amide bond formed between the $-COOH$ group of one amino acid molecule and the $-NH_2$ group of another amino acid molecule by the elimination of a water molecule is called a peptide linkage. For example,the reaction between Valine and Alanine forms a dipeptide with a peptide linkage.
$(ii)$ Primary structure: The primary structure of a protein refers to the specific sequence in which various amino acids are linked together in a polypeptide chain. Each protein has a unique sequence of amino acids,and any change in this sequence results in a different protein.
$(iii)$ Denaturation: In a biological system,a protein exists in a unique $3-D$ structure with specific biological activity,known as a native protein. When this native protein is subjected to physical changes (like temperature change) or chemical changes (like $pH$ change),its hydrogen bonds are disturbed. This causes the globules to unfold and the helix to uncoil,leading to the loss of biological activity. This process is called denaturation. During denaturation,the secondary and tertiary structures are destroyed,but the primary structure remains intact. An example is the coagulation of egg white upon boiling.