The Thermodynamic Point of View of Aging

– Entropy As The Driving Force

Living organism is an open system (non-isolated system) with mass, and energy flow into and out of the system, i.e.. mass and energy exchange with its “surrounding. Non-equilibrium thermodynamics is a branch of thermodynamics concerned with studying time-dependent thermodynamic systems, irreversible transformations and open systems. Living organisms are non-equilibrium open systems until life goes into dead to reach equilibrium and max entropy. The second law of thermodynamics is an expression of the universal principle of increasing entropy of the universe. Of the many different expressions or  versions of the second law, they all explain the same phenomenon of irreversibility in nature and predict the direction of spontaneously occurred process (e.g.. biochemical reactions). To prevent entropy from increasing in a system  and to maintain “order”, energy has to inflow into the “system” from its “surrounding”. The entropy increasing is a form of energy dispersal.

There is a huge body of knowledge supporting the belief that age changes are characterized by increasing entropy, which results in the random loss of molecular fidelity, and accumulates to slowly overwhelm maintenance systems. The common denominator that underlies all modern theories of biological aging is change in molecular structure and, hence, function. These changes are the result of entropic changes, which is now supported by the recent reinterpretation of the Second Law of Thermodynamics, where the belief that it only applies to closed systems has been overturned.

Dr. Hayflick states: “Entropy is the tendency for concentrated energy to disperse when unhindered regardless of whether the system is open or closed. The hindrance of entropic change resides in the relative strength of chemical bonds in a molecule. The prevention of chemical bond breakage, among other structural changes, is absolutely essential for life. Through evolution, natural selection has favored energy states capable of maintaining functionality in most molecules until reproductive maturation, after which there is no species survival for those energy states to be maintained indefinitely. The dispersal of energy may result in a biologically inactive or malfunctioning molecule. Energy dispersal is never entirely eliminated but it can be circumvented for varying time periods by repair or replacement processes. From the standpoint of a physicist, a lowered energy state is not necessarily disorder, because it simply results in the identical molecule with a lowered energy state. The fact that such a molecule might be biologically inactive may not concern the physicist, but it definitely does concern the biologist and, especially, the biogerontologist. The aging process occurs because the changed energy states of biomolecules renders them inactive or malfunctioning. Identical events also occur before the aging phenotype appears, but repair and replacement processes are capable of maintaining the balance in favor of functioning molecules; otherwise, the species would vanish. After reproductive maturation, this balance slowly shifts to one in which molecules that lose their biologically active energy states are less likely to be replaced or repaired. The diminution of repair and replacement capability is further exacerbated, because the enormously complex biomolecules that compose the repair and replacement systems also suffer the same fate as their substrate biomolecules.”