Most important basic building block of a cell. Proteins are a class of macromolecules that give the cell its structure, interconvert chemical substances, receive signals, are messenger substances, or act as antibodies as part of the immune defense. Proteins are made up of amino acids that are arranged like pearls on a string. This string coils and folds upon itself until it gives rise to the shape the protein needs to be able to fulfil its function in the body. The information about the amino acid sequence in a protein is encoded by the corresponding gene.