The living cell is the smallest DNA-based molecular computer in existence.This conjecture was based on the similarities found between the cell and the computer at 15-20 levels of organization.A molecular computer can be defined as a molecular system capable of utilizing chemical free energy to convert input signals (e.g.,neurotransmitters,hormones,cytokines) to output processes (e.g.,depolarization,hyperpolarization,cell growth,migration,differentiation,secretion,shape changes,mitosis,apoptosis,etc.),following a set of molecular instructions encoded in biopolymers (DNA,RNA,proteins).Just as machine computing requires hardware,software and electricity,so cell computing depends on physicochemical structures of biopolymers as hardware,the genetic information encoded in biopolymers as software,and exergonic chemical reactions catalyzed by enzymes as the source of free energy.