energy metabolism


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Energy metabolism

Energy metabolism, or bioenergetics, is the study of energy changes that accompany biochemical reactions. Energy sustains the work of biosynthesis of cellular and extracellular components, the transport of ions and organic chemicals against concentration gradients (osmotic work), the conduction of electrical impulses in the nervous system, and the movement of cells and the whole organism. Sunlight is the ultimate source of energy for life. Photosynthetic cells use light energy to produce chemical energy and reducing compounds, used to convert carbon dioxide into organic chemicals such as glucose. The energy from the oxidation of carbohydrates, fats, and proteins sustains the biochemical reactions required for life.

The main sources of chemical energy for most organisms are carbohydrates, fats, and protein. Energy content is expressed in calories or joules. The nutritional calorie, or kilocalorie (kcal), in foodstuffs is equivalent to 1000 calories. The energy content per gram of carbohydrate is 4 kcal (16 J); protein, 4 kcal (16 J); and fat, 9 kcal (36 J). The metabolism of foodstuffs yields chemical energy and heat.

Energy is defined as the ability to do work, and metabolism represents the biochemical reactions that a cell can perform to produce energy. The most important thermodynamic parameter in bioenergetics is the free energy change, ΔG, occurring at constant temperature and pressure (the usual conditions for chemical reactions inside the cell). The Gibbs free energy change is defined as the free energy content of the final state minus the free energy content of the initial state.

All feasible reactions occur with a negative free energy change; the final state has less free energy than the initial state; that is, ΔG < 0 (process is exergonic). If the free energy of the final state is more than that of the initial state, ΔG is positive and the reaction is not feasible without the input of energy; ΔG > 0 (process is endergonic). When the free energy change is zero, the reaction or process is at equilibrium; ΔG = 0 (process is isoergonic).

The complete oxidation of one mole of glucose to carbon dioxide and water is associated with the liberation of free energy. Energy is released in a stepwise fashion and is coupled to the biosynthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (Pi). The reaction of ATP with water to produce ADP and Pi results in the liberation of a large amount of energy (30 kJ, or 7 kcal per mole). Such compounds are said to be energy-rich and to possess a high-energy bond. Lipmann's law is the cornerstone of energy metabolism: ATP serves as the common currency of energy exchange in living systems (animals, plants, and bacteria). The ATP-ADP couple receives and distributes chemical energy in all living systems. Creatine phosphate is an energy-rich compound found in vertebrate muscle and brain; it is a storage form of chemical energy and can energize the regeneration of ATP from ADP. Such a reaction occurs in vigorously exercising skeletal muscle when ATP is expended to produce contraction. See Adenosine diphosphate (ADP), Adenosine triphosphate (ATP)

energy metabolism

[′en·ər·jē mə′tab·ə‚liz·əm]
(biochemistry)
The chemical reactions involved in energy transformations within cells.
References in periodicals archive ?
Many animals regulate energy metabolism by altering RMR in order to adapt to changing environment (Nagy and Pistole, 1988).
Researchers have circumvented this situation by measuring aerobic energy metabolism after intense exertion, a measure called EPOC (excess post-exercise oxygen consumption).
The simple layout contains nine chapters divided into three sections: energy yielding nutrients, estimation of energy requirements, and physiological aspects of energy metabolism.
Energy metabolism is also very important because it depends on reserves accumulated and on environmental conditions.
Coverage includes an historical overview of knowledge management and mathematical modeling in biology, the basic biological cellular network concepts in the context of cellular functioning, explanation of the Edinburgh Pathway Editor (EPE) software package for pathway visualization and illustration, construction and verification of kinetic models, the main features and user interface of DBSolve, modeling of individual enzymes and transporters, pathways kinetic modeling, modeling of mitochondrial energy metabolism, and application of the kinetic modeling approach to biotechnology and biomedicine.
Origin targets including mitochondria production of reactive oxygen species, antioxidant potentia, membrane potential, energy metabolism, mitochondrial respiratory enzymes activities and mitochondria swelling degree were evaluated.
Valle's team then compared activity levels of hundreds of proteins in the animals' livers, which help to regulate energy metabolism.
Valle's team then compared the activity levels of hundreds of proteins in the animals' livers, which help to regulate energy metabolism.
According to the document, "DVIC has concluded that the facts of this case meet the statutory criteria for demonstrating that the vaccinations [the child] received on July 19, 2000, significantly aggravated an underlying mitochondrial disorder, which predisposed her to deficits in cellular energy metabolism, and manifested as a regressive encephalopathy with features of autism spectrum disorder.
Bennett's research has been the investigation of inborn errors of mitochondrial energy metabolism with a special emphasis on disorders of fatty acid metabolism.
In view of the key role played by the enzymes, ATPase and Cytochrome-c-oxidase in energy metabolism, an attempt was made to study the activity levels in rat tissues under Dox stress.
Lipoic acid, a critical cofactor in three vital enzyme complexes that control energy metabolism, is synthesized in both plants and animals.

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