a nucleoside composed of the pentose sugar d
-ribose and adenine. It is a structural subunit of ribonucleic acid
(RNA). Adenosine nucleotides are involved in the energy metabolism of all cells. Adenosine can be linked to a chain of one, two, or three phosphate groups to form adenosine monophosphate
(AMP), adenosine diphosphate
(ADP), or adenosine triphosphate
(ATP). The bond between the phosphate groups in ADP or the two bonds between phosphate groups in ATP are called high-energy bonds,
because hydrolysis of a high-energy bond provides a large amount of free energy that can be used to drive other processes that would not otherwise occur. The energy that is derived from the breakdown of carbohydrates, fats, or proteins is used to synthesize ATP. The energy stored in ATP is then used directly or indirectly to drive all other cellular processes that require energy, of which there are four major types: (1) the transport of molecules and ions across cell membranes against concentration gradients, which maintains the internal environment of the cell and produces the membrane potential for the conduction of nerve impulses; (2) the contraction of muscle fibers and other fibers producing the motion of cells; (3) the synthesis of chemical compounds; (4) the synthesis of other high-energy compounds.
a preparation of adenosine, which acts as a cardiac depressant of automaticity in the sinus node and conduction in the atrioventricular node and as a vasodilator
. It is used as an antiarrhythmic
and is also used to cause coronary vasodilation during myocardial perfusion imaging
in patients who cannot exercise adequately to perform an exercise stress test
, administered intravenously.
cyclic adenosine monophosphate a cyclic nucleotide, adenosine 3′,5′-cyclic monophosphate, involved in the action of many hormones, including catecholamines, ACTH, and vasopressin. The hormone binds to a specific receptor on the cell membrane of target cells. This activates an enzyme, adenylate cyclase, which produces cyclic AMP from ATP. Cyclic AMP acts as a second messenger activating other enzymes within the cell. Abbreviated 3′,5′-AMP, cAMP, and cyclic AMP.
(ADP) a nucleotide, adenosine 5′-pyrophosphate, produced by the hydrolysis of adenosine triphosphate (ATP). It is then converted back to ATP by the metabolic processes oxidative phosphorylation, glycolysis, and the tricarboxylic acid cycle
(AMP) a nucleotide, adenosine 5′-phosphate, involved in energy metabolism and nucleotide synthesis. Called also adenylic acid
adenosine triphosphatase (ATPase) a term used to refer to the enzymatic activity of certain intercellular processes that split ATP to form ADP and inorganic phosphate, when the energy released is not used for the synthesis of chemical compounds. Examples are the splitting of ATP in muscle contraction and the transport of ions across cell membranes.
adenosine triphosphate (ATP) a nucleotide, adenosine 5′-triphosphate, occurring in all cells, where it stores energy in the form of high-energy phosphate bonds. Free energy is supplied to drive metabolic reactions, to transport molecules against concentration gradients (active transport), and to produce mechanical motion (contraction of myofibrils and microtubules), when ATP is hydrolyzed to ADP and inorganic phosphate or to AMP and inorganic pyrophosphate. ATP is also used to produce high-energy phosphorylated intermediary metabolites, such as glucose 6-phosphate.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
storage lesion Transfusion medicine The constellation of changes occurring in a unit of packed red cells during storage. See Red cell preservatives.
↑ Ammonium to 470 µmol/L–US: 800 µg/dL
↑ Free Hb in plasma from 82 to 6580 mg/L–US: 8.2 to 658 mg/dL
↑ K+ from 4.2 to 78.5 mmol/L–US: 4.2 to 78.5 mEq/L
↓ ATP from 100% to 45%
↓ 2,3 DPG to < 10% of original levels–replenished within 24 hours of transfusion
↓ Labile proteins, eg complement, fibronectin and coagulation factors ↓ to negligible
↓ Na+ from 169 to 111 mmol/L–US: 169 to 111 mEq/L
↓ pH from 7.6 to 6.7
Adverse physiologic effects of stored blood is negligible in the absence of a previous compromise of the Pt's–recipient's status
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
Fig. 55 ATP
. The structure of ATP
ATP (adenosine triphosphate) a molecule consisting of ADENINE and ribose sugar on to which are attached three phosphate groups, two being joined by high-energy bonds (see Fig. 55 ). HYDROLYSIS of these special bonds results in the release of energy. ATP molecules are formed in two main processes, both involving the addition of inorganic phosphate to ADP via a high energy bond:
ATP can be formed during CELLULAR RESPIRATION, either in the general cytoplasm during GLYCOLYSIS or in the MITOCHONDRIA via the KREBS CYCLE and the ELECTRON TRANSPORT SYSTEM if oxygen is present. ATP is also formed during photosynthesis in the CHLOROPLASTS of green plants, again using an electron transport system. ATP molecules act therefore as short-term ‘biological batteries’, retaining energy until required for such processes as active transport, synthesis of new materials, nerve transmission, and muscle contraction. An active cell requires more than two million molecules of ATP per second to drive its biochemical machinery.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005