Small molecules of the average cell Varieties: (1) precursors (building blocks) of macromolecules; (2) metabolic intermediates; (3) enzyme cofactors; (4) polyamines bound to DNA Approximate number of kinds of small molecules: (1) 120 amino acids, their precursors and derivatives; (2) 100 nucleotides, their precursors and derivatives; (3) 50 fatty acids and their precursors; (4) 250 sugars, carbohydrates, and their precursors; (5) 300 quinones, polyisoprenoids, prophyrins, vitamins, other coenzymes and prosthetic groups, and their precursors