Bioenergetics

Overview
Bioenergetics is the subject of a field of biochemistry that concerns energy flow through living systems. This is an active area of biological research that includes the study of thousands of different cellular processes such as cellular respiration and the many other metabolic processes that can lead to production and utilization of energy in forms such as ATP molecules. All biological processes including the chemical reactions of bioenergetics obey the "laws" of thermodynamics.

Growth, development and metabolism are some of the central phenomena in the study of biological organisms. The role of energy is fundamental to such biological processes. The ability to harness energy from a variety of metabolic pathways is a property of all living organisms. Life is dependent on energy transformations; living organisms survive because of exchange of energy within and without.

In a living organism chemical bonds are broken and made as part of the exchange and transformation of energy. The chemical bonds in carbohydrates, including sugars, are important for the storage of energy. Other chemical bonds that are important for metabolism include the terminal phosphate bonds of ATP and the energy-rich bonds of fats and oils. These molecules, along with oxygen, are important energy sources for many biological processes. Utilization of chemical energy from such molecules powers biological processes in every biological organism. Bioenergetics is the part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the molecules found in biological organisms.

Food molecules are sources of chemical energy for many organisms. 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 of food chains involve energy transformations within ecosystems and the term "bioenergetics" is also applied to such large-scale transformations of energy.

Chemiosmotic theory
One of the major triumphs of bioenergetics is Peter D. Mitchell's chemiosmotic theory of how protons in aqueous solution function in the production of ATP in cell organelles such as mitochondria. Other cellular sources of ATP such as glycolysis were understood first, but such processes for direct coupling of enzyme activity to ATP production are not the major source of useful chemical energy in most cells. Chemiosmotic coupling is the major energy producing process in most cells, being utilized in chloroplasts and many single celled organisms in addition to mitochondria.

Additional reading

 * "Bioenergetics: The Molecular Basis of Biological Energy Transformations (2nd Edition)" by Albert L. Lehninger. Publisher: Addison-Wesley (1971)
 * "Bioenergetics (3rd Edition)" by David G. Nicholls and Stuart J. Ferguson. Publisher: Academic Press (2002)
 * Universal energy principle of biological systems and the unity of bioenergetics by D E Green and H D Zande in Proceedings of the National Academy of Sciences U S A (1981) Volume 78 pages 5344–5347.