A quaternary structure is a protein that has two or more coils of peptide chains. Different types of bonds bind the chains into a specific shape, forming one of the two types of quaternary proteins: fibrous and globular.
Keratins are fibrous proteins that are held together by coiled amino acid chains. Keratins are contained in hair, skin, wool, fur, wool, nails, beaks and feathers. They are also found in muscle tissue and are needed for blood to clot. Globular proteins consist of clusters of different types of structures that form round bundles. Globular proteins are present in insulin, most enzymes and hemoglobin, a substance found in red blood cells.