The $\alpha$-amino acids are the building blocks of proteins. All $\alpha$-amino acids exist as zwitter ion due to which they show amphoteric behaviour. All amino acids are joined through peptide bond. Proteins are broadly classified as globular proteins and fibrous proteins. Globular proteins are water soluble, whereas fibrous proteins are not. The complete structure of protein is discussed at four different levels i.e. primary, secondary, tertiary and quaternary structures. Protein loses its biological activity in denatured form. (a) Define the following : (i) Peptide linkage (ii) Denatured protein (b) Why do amino acids show amphoteric behaviour ? (c) (i) How can you differentiate between Fibrous protein and Globular protein ? OR (c) (ii) Write the names of two different secondary structures of proteins.