Proteins have many biological functions, including facilitating transportation, delivering key nutrients and acting as storage facilities. The role that proteins play varies on their shape, size and orientation as well as the type of cell that they inhabit.
Proteins play important roles in plants by storing nutrients in their seeds. In some animal cells and tissues, proteins store iron and other nutrients. Contractile proteins help cells and organisms move by facilitating muscle contraction. Transport proteins are found in all living species: they bring substances such as blood, water and glucose from one destination to the next and reside in plasma and intracellular membranes.