How does the protein structure of fibrous and globular proteins differ, and how does this affect their function?

When we answer this question we need to focus on the differences in interactions that create the tertiary and quaternary structure of fibrous and globular proteins. For example, fibrous proteins are characterised by long polypeptide chains that are closely linked, hence making the protein insoluble and strong, whilst globular proteins are characterised by a hydrophilic, spherical shape formed by differing polypeptide chains. The primary structure of fibrous proteins involves many repeating chains of amino acids, whilst their tertiary and quaternary structure involves a lot of hydrogen bonding, as well as disulfide bridges and ionic bonds, to form connected, parallel chains. In comparison, the primary structure of globular proteins is more varied, whilst the tertiary and quaternary structure involves hydrophobic/hydrophilic interactions so that the hydrophobic R groups fold into the inside, creating the spherical structure. Additionally, globular proteins are often associated with prosthetic groups, which are inorganic components that are attached to the quaternary structure of the protein.These characteristics determines the general function of fibrous globular proteins. Fibrous proteins are mainly used as structural proteins due to their insolubility and strength, meaning they are formidable against damage and create water-tight seals, as well as their long polypeptide chains being ideal for large biological structures. An example of a fibrous protein is collagen, which consists of three polypeptide chains wound around each other and connected by strong hydrogen bonding, making it ideal for its function as the structural unit of bones, cartilage, and connective tissue. In comparison, globular proteins mainly have metabolic functions (e.g. enzymes), due to their solubility, allowing them to travel in the blood, whilst the more varied amino acid makeup and prosthetic groups allows the protein to interact with the necessary molecules. An example of a globular protein is haemoglobin, which is made up of two alpha polypeptide, and two beta polypeptide chains, all of which have a prosthetic haem group which binds to oxygen molecules.