Bioenergetics

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 law of thermodynamics.

Thermodynamics

*First Law is the conservation of energy: energy can neither be created nor destroyed.

*Second Law states that the degree of disorder or entropy (S) of a closed system or of the universe as a whole can only increase. [ [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=388525 The Second Law of Thermodynamics in Bioenergetics] by Gabor Kemeny in Proceedings of the National Academy of Sciences U S A (1974) Volume 71 pages 2655–2657.]

Overview

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.

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. Energy is available for work (such as mechanical work) or for other processes (such as chemical synthesis and anabolic processes in growth, when weak bonds are broken and stronger bonds are made. The production of stronger bonds allows release of usable energy.

The chemical bonds in carbohydrates, including sugars, are important for the storage of energy, as are the bonds of fats and oils. These molecules, in combination with oxygen, are important energy sources for many biological processes. The bonds holding the molecules of carbohydrates and fats together, and the bonds holding molecules of free oxygen together, are all relatively weak compared with the chemical bonds which hold carbon dioxide and water together. Thus, "burning" of carbohydrates and fats with oxygen generates net energy from the formation of stronger bonds. This net energy may evolve as heat, or some of which may be used by the organism for other purposes, such as breaking other bonds to do chemistry.

Other chemical bonds that are important for metabolism include the terminal phosphate bonds of ATP. These bonds are again relatively week compared with the stronger bonds formed when ATP is broken down to adenosine monophosphate and phosphate, disolved in water. Here is it is the energy of hydration which results in energy release. This hydrolysis of ATP is used as a battery to store energy in cells, for intermediate metabolism.

Utilization of chemical energy from such molecular bond rearrangement powers biological processes in every biological organism.

Food molecules are sources of chemical energy for many organisms. Not all metabolizable energy is available for the production of ATP. [ [http://www.fao.org/docrep/006/Y5022E/y5022e04.htm CHAPTER 3: CALCULATION OF THE ENERGY CONTENT OF FOODS - ENERGY CONVERSION FACTORS ] ]

Types of Reactions

*Exergonic is a spontaneous reaction that releases energy. It is thermodynamically favored. On the course of a reaction, energy needs to be put in, this activation energy drives the reactants from a stable state to a highly energetic unstable configuration. These reactants are usually complex molecules that are broken into simpler products. The entire reaction is usually catabolic. The release of energy, also called free energy is a - ΔG because energy is lost from the bonds formed by the products.

*Endergonic is an anabolic reaction that consumes energy. It has a +ΔG because energy is required to break bonds.

The free energy ( ΔG) gained or lost in a reaction can be calculated: ΔG= ΔH - T ΔS.

Also, ΔG = ΔG˚' + 2.303RTlog( [P] / [R] ) where

**R is the gas constant, 1.987 cal/mol
**T is temperature in Kelvin K = 273 + ˚C
**P is Products
**R is the reactants

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 [cite journal | author=Peter Mitchell | title=Coupling of phosphorylation to electron and hydrogen transfer by a chemi-osmotic type of mechanism | journal=Nature | year=1961 | volume=191 | issue= | pages= 144–148 | url= | doi=10.1038/191144a0 Entrez Pubmed|13771349] . 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.

References

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)
* [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=348741 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.

See also

*Cellular respiration
*Photosynthesis
*ATP synthase
*Active transport
*Myosin

External links

*The Molecular & Cellular Bioenergetics Gordon Research Conference ( [http://www.grc.org/conferences.aspx?id=0000022 see] ).