OverviewBioenergetics is the part of biochemistry concerned with the energy involved in making and breaking of chemical bonds in the molecules found in biological organisms.
Cell growth|Growth, Developmental biology|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 anabolism|anabolic processes in growth), when weak bonds are broken and stronger bonds are made. The production of stronger bonds allows release of usable energy.
Living organisms obtain energy from organic and inorganic materials. For example, lithotrophs can oxidize minerals such as nitrates or forms of sulfur, such as elemental sulfur, sulfites, and hydrogen sulfide to produce ATP. In photosynthesis, autotrophs can produce ATP using light energy. Heterotrophs must consume organic compounds. These are mostly carbohydrates, fats, and proteins. The amount of energy actually obtained by the organism is lower than the Food energy|amount present in the food; there are losses in digestion, metabolism, and thermogenesis.*The materials are generally combined with oxygen to release energy, although some can also be oxidized anaerobically by various organisms. The bonds holding the molecules of nutrients together and the bonds holding molecules of free oxygen together are all relatively weak compared with the chemical bonds holding carbon dioxide and water together. The utilization of these materials is a form of slow combustion. That is why the energy content of food can be estimated with a bomb calorimeter. The materials are oxidized slowly enough that the organisms do not actually produce fire. The oxidation releases energy because stronger bonds have been formed. 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.
Living organisms produce ATP from energy sources via oxidative phosphorylation. The terminal phosphate bonds of ATP are relatively weak compared with the stronger bonds formed when ATP is broken down to adenosine monophosphate and phosphate and then dissolved in water. Here it is the energy of hydration that results in energy release. An organism's stockpile 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.
Types of reactions
The free energy (?G) gained or lost in a reaction can be calculated: ?G = ?H - T ?S.
Also, ?G = ?G░' + 2.303RT log([P]/[R]) where
CotransportIn August 1960, Robert K. Crane presented for the first time his discovery of the sodium-glucose Co-transport|cotransport as the mechanism for intestinal glucose absorption.* Robert K. Crane|Crane's discovery of Co-transport|cotransport was the first ever proposal of flux coupling in biology and was the most important event concerning carbohydrate absorption in the 20th century.*
Chemiosmotic theoryOne of the major triumphs of bioenergetics is Peter D. Mitchell's Chemiosmosis|chemiosmotic theory of how protons in aqueous solution function in the production of ATP in cell organelles such as Mitochondrion|mitochondria.* This work earned Mitchell the 1978áNobel Prize for Chemistry. 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 several Three-domain system|single celled organisms in addition to mitochondria.
Energy balanceEnergy balance (biology)|Energy balance is the Homeostasis#Biological|biological homeostasis of energy in living systems. It is measured with the following equation:
Energy intake = internal heat produced + external work + storage.