ATP

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ATP (adenosine triphosphate) A nucleotide that is of fundamental importance as a carrier of chemical energy in all living organisms. It consists of adenine linked to D-ribose (i.e. adenosine); the D-ribose component bears three phosphate groups, linearly linked together by covalent bonds (see formula). These bonds can undergo hydrolysis to yield either a molecule of ADP (adenosine diphosphate) and inorganic phosphate or a molecule of AMP (adenosine monophosphate) and pyrophosphate (see ATPase). Both these reactions yield a large amount of energy (about 30.6 kJ mol–1) that is used to bring about such biological processes as muscle contraction, the active transport of ions and molecules across plasma membranes, and the synthesis of biomolecules. The reactions bringing about these processes often involve the enzyme-catalysed transfer of the phosphate group to intermediate substrates, for example by a kinase enzyme. Most ATP-mediated reactions require Mg2+ ions as cofactors.

ATP is regenerated by the rephosphorylation of AMP and ADP using the chemical energy obtained from the oxidation of food. This takes place during glycolysis and the Krebs cycle but, most significantly, is also a result of the reduction–oxidation reactions of the mitochondrial electron transport chain, which ultimately reduces molecular oxygen to water (oxidative phosphorylation). ATP is also formed by the light-dependent reactions of photosynthesis.

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ATP Adenosine triphosphate, the coenzyme that acts as an intermediate between energy‐yielding (catabolic) metabolism (the oxidation of metabolic fuels) and energy expenditure as physical work and in synthetic (anabolic) reactions. ADP (adenosine diphosphate) is phosphorylated to ATP linked to oxidation; in energy expenditure ATP is hydrolysed to ADP and phosphate ions.

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ATP (adenosine triphosphate) n. a compound that contains adenine, ribose, and three phosphate groups and occurs in cells. The chemical bonds of the phosphate groups store energy needed by the cell, for muscle contraction; this energy is released when ATP is split into ADP or AMP. ATP is formed from ADP or AMP using energy produced by the breakdown of carbohydrates or other food substances. See also mitochondrion.

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ATP Biochem. adenosine triphosphate
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ATP • abbr. Biochem. adenosine triphosphate.

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