Primary Structure: The specific sequence in which the various α-amino acids present in a protein are linked to one another is called its primary structure. Any change in the primary structure creates a different protein.
Secondary Structure: The conformation which the polypeptide chain assumes as a result of hydrogen bonding is known as secondary structure. The two types of secondary structures are α-helix and β -pleated sheet structure. In α-helix structure, the polypeptide chain forms all the possible hydrogen bonds by twisting into a right handed screw (helix) with the —NH groups of each amino acid residue hydrogen bonded to the 
groups of an adjacent turn of the helix. In b-pleated structure, all peptide chains are stretched out nearly to maximum extension and then laid side by side which are held together by hydrogen bonds.
