Types of proteins

Beyond their chemical composition (the sequence of amino-acid residues, discussed from section 14.3.4a onward), proteins can also be classified more simply by the overall molecular SHAPE their polypeptide chain(s) fold or coil into. On this basis, proteins fall into two broad structural types: globular proteins, whose molecules are folded into a compact, roughly spherical shape, and fibrous proteins, whose molecules are held in an elongated, rod-like shape. These two shape-classes correlate strongly with solubility and biological role -- globular proteins tend to be soluble, mobile, functional molecules (enzymes, transport proteins, hormones), while fibrous proteins tend to be insoluble, structural molecules …