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 ?
Although SSYX at different drug concentrations was used in this study, due to the limited number of experimental groups, the optimal concentration of SSYX for regulating myocardial energy metabolism was not explored.
Effects of tannic acid food on energy metabolism in Brandt's voles (Lasiopodomys brandtii).
Cancer is a disease of defective cellular energy metabolism. Most genomic effects found in cancer arise as secondary downstream effects of defective energy metabolism (Seyfried et al, 2010).
A total of 13 metabolites were identified, involving energy metabolism (Cre, creatine; Suc, succinate; Ala, alanine; Lac, lactate), neurotransmitters (Asp, aspartate; Glu, glutamate; Gln, glutamine; GABA, y-aminobutyric acid; Gly, glycine), and membrane metabolism (Cho, choline; NAA, N-acetylaspartate) as well as osmoregulation (Myo, myoinositol; Tau, taurine).
Thus, it has been postulated that bone, energy metabolism, and reproduction may be interrelated [22, 23].
Vionica has been tested and proven to provide a boost of essential mineral complexes and two non-essential organic nutrients, increasing aerobic energy metabolism and resulting in better performance in the pool of female runners that have trialed the product.
A number of possible mechanisms of action are identified in the review by which gut microbiota are associated with DM, including through energy metabolism, inflammation, gut permeability, and the immune system.
"Among older women with diabetes for whom the glucose-based energy metabolism promoted by estrogen is already compromised, this downregulation of alternative energy sources may lead to increased atrophy of gray matter, which has a greater metabolic demand relative to white matter," Dr.
"The report by LeBleu and Kalluri described in this article now suggests that cancer cells that acquire the ability to metastasize appear to further co-opt cellular energy metabolism by augmenting mitochondrial respiration through over-expression of a transcription coactivator known as peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1a).
Roberts, director of the Energy Metabolism Laboratory and professor at the School of Nutrition Science and Policy at Tufts, who also is an adjunct professor of psychiatry.
They cover the sources, production, and microencapsulation of probiotics; sources and production of prebiotics; the analysis of probiotics and prebiotics; their regulation and guidelines; their role in infant and elderly nutrition, animal nutrition, immune system protection, pediatric diarrheal disorders, gastrointestinal diseases, infections, cancer prevention, allergy and asthma, Crohn's disease, genitourinary health, obesity, energy metabolism, and lipid metabolism; their interactions with minerals; the role of gut microbiota; effects on Heliobacter pylori infection; and genomics.
In mammals, for example, sleep-awake pattern, blood pressure and heart rate, hormone secretion, body temperature, and energy metabolism exhibit circadian oscillation.

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