14.20 Define the following as related to proteins (i) Peptide linkage (ii) Primary structure (iii) Denaturation.

<p><strong>14.20&nbsp;</strong></p><p>When two molecule of –amino acids similar or different combine in this way that the amino group of one molecule with carboxy group of the other molecule, this result in the elimination of water molecule and the formation of new bond-CO NH- .</p><p>This type of bond is called peptide bond or peptide linkage. The product of reaction is called dipeptide. For example, COOH group of valine combine with NH₂ group of alanine, we get dipeptide Valylalanine (Val-Ala) as final product, as shown below:-</p><p><picture><img src="https://images.shiksha.com/mediadata/images/articles/1686816443phpGlrXZ1.jpeg" alt="" width="260" height="153"></picture></p><p><strong>2-</strong> Proteins may have one or more polypeptide chains. Each polypeptide in a protein has amino acids linked with each other in a specific sequence and due to this sequence of amino acids the structure of proteins is said to be primary structure.</p><p>Any change in this sequence of amino acids creates different proteins. In other words, the sequence in which various amino acids are arranged in a protein is called primary structure. The amino acid sequence of a protein determines its function and it’s critical of its biological activity.</p><p><strong>3-</strong> Each protein in the biological system has a unique 3-D structure and has specific biological This is called native form of a protein. When a protein in its native form is subjected to physical changes such as change in temperature, pH, etc.</p><p>hydrogen bonds are broken. Due to cleavage of hydrogen bonds, unfolding of protein molecule occurs and the protein loses its biological activity. This loss of biological activity is called denaturation. During denaturation, 2- degree and 3-degree structures of proteins are destroyed but 1-degree structure remains intact.</p><p>As a result of denaturation, globular proteins are converted into fibrous proteins. In other words, denaturation leads to coagulation. That is why coagulated proteins are also called denaturated proteins.</p>

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