Elastic fibres contains the fibrous protein elastin.Elastic fibres are found in the walls of blood vessels, in the walls of the alveoli in the lungs.Elastic fibres are flexible and can stretch and recoil to accommodate larger volumes of blood or air without breaking.Elastin has a quaternary structure. It is made form many stretchy molecules called tropoelastin.Many soluble tropoelastin fibres are cross-linked to make a large, insoluble and stable structure.The tropoelastin contains alternate hydrophobic and lysine rich areas. Lysine residues are able to form covalent cross-links.The hydrophobic regions interact with hydrophobic regions of other tropoelastin molecules.Skin and other tissues in the body contain elastin for strength and elasticity.