Describe the structure of proteins

Proteins are polymers of Aminoacids. Aminoacids are joined in condensation reactions (water is eliminated) by peptide bonds. The primary structure is the order of aminoacids in the protein, while the secondary structure is the folding of the polypeptide chain into alpha helix and beta pleated sheets which are held together by hydrogen bonds. The tertiary structure is the 3D shape of the polypeptide chain due to hydrogen and ionic bonds. The folding of 2 or more polypeptide chains represents the quaternary structure of a protein.