Biological thermodynamics

In thermodynamics, biological thermodynamics (Greek: bios = life and logikos = reason + Greek: thermos = heat and dynamics = power) or bioenergetics is the study of energy transformation in the biological sciences. More definitively, biological thermodynamics may be defined as the quantitative study of the energy transductions that occur in and between living organisms, structures, and cells and of the nature and function of the chemical processes underlying these transductions. Biological thermodynamics may address the question of whether the benefit associated with any particular phenotypic trait is worth the energy investment it requires.

History
German-British medical doctor and biochemist Hans Krebs' 1957 book Energy Transformations in Living Matter (written with Hans Kornberg) was the first major publication on the thermodynamics of biochemical reactions. In addition, the appendix contained the first-ever published thermodynamic tables, written by K. Burton, to contain equilibrium constants and Gibbs free energy of formations for chemical species, able to calculate biochemical reactions that had not yet occurred.

Bioenergetics
Growth, development and metabolism are some of the central phenomena in the study of biological organisms. Living cells and organisms must perform work to stay alive, to grow, and to reproduce themselves. The energy concept is useful to explain such biological processes. The ability to harness energy from a variety of metabolic pathways and channellize it into activities of organism is a fundamental property of all living organisms. Sustenance of life is critically dependent on energy transformations; living organisms survive because of exchange of energy within and without.

In a living organism chemical bonds are constantly broken and made to make the exchange and transformation of energy possible. These chemical bonds are most often bonds in carbohydrates, including sugars. Other chemical bonds include bonds in chemical compounds that are important for metabolism, for example, those in a molecule of ATP or fats and oils. These molecules, along with oxygen, are common stores of concentrated energy for the biological processes. One can therefore assert that transformation of energy from a more to a less concentrated form is the driving force of all biological processes or chemical processes that are responsible for the life of a biological organism. Molecular biology and biochemistry are in fact scientific studies concerning the making and breaking of chemical bonds in the molecules found in biological organisms.

Non-equilibrium thermodynamics has been applied for explaining how biological organisms can develop from disorder. Even with the application of Onsager reciprocal relations the classical principles of equilibrium thermodynamics show that systems close to equilibrium always develop into states of disorder which are stable to perturbations and cannot explain the occurrence of ordered structures.

Ilya Prigogine developed the methods for the thermodynamic treatment of such systems, he called these systems dissipative systems, because they are formed and maintained by the dissipative processes which take place because of the exchange of energy between the system and its environment and because they disappear if that exchange ceases. They may be said to live in symbiosis with their environment. Energy transformations in biology are primarily due to the chemical synthesis and decompositions that are brought about by the energy absorbed by organisms from sunlight through insolation and photosynthesis. The total energy captured by photosynthesis in green plants from the solar radiation is about 2 x 10 23 joules of energy per year. Annual energy captured by photosynthesis in green plants is about 4% of the total sunlight energy which reaches Earth. The energy transformations in biological communities surrounding hydrothermal vents are exceptions. They oxidize sulfur, obtaining their energy via chemosynthesis rather than photosynthesis. The oxygen used to do this is photosynthetically derived, but the sulfur in the thermodynamically unstable, non-oxidized state exists due to geothermal energy.

Food, ingested by an organism contains several chemical substances and hence has chemical energy. Not all metabolizable energy is available for the production of ATP. Some energy is utilized during the metabolic processes associated with digestion, absorption and intermediary metabolism of food and can be measured as heat production; this is referred to as dietary-induced thermogenesis (DIT), or thermic effect of food, and varies with the type of food ingested. The predator-prey relationships, food chains, are in effect energy transformations within ecosystems.

The focus of thermodynamics in biology
The field of biological thermodynamics is focussed on thermodynamic applications of the principles of chemical thermodynamics in biology and biochemistry. Principles covered include the first law of thermodynamics, the second law of thermodynamics, Gibbs free energy, statistical thermodynamics, reaction kinetics, and on hypotheses of the origin of life. Presently, biological thermodynamics concerns itself with the study of internal biochemical dynamics as: ATP hydrolysis, protein stability, DNA binding, membrane diffusion, enzyme kinetics, and other such essential energy controlled pathways. Thermodynamically, the amount of energy capable of doing work during a chemical reaction is measured quantitatively by the change in the Gibbs free energy. The physical biologist Alfred Lotka attempted to unify the change in the Gibbs free energy with evolutionary theory.