adenosine triphosphate adenosine triphosphate adenosine triphosphate (atp) is an organic compound that provides energy to drive and support many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. found in all known forms of life, atp is often referred to as the "molecular unit of currency" of intracellular energy transfer. when consumed in metabolic processes, it converts either to adenosine diphosphate (adp) or to adenosine monophosphate (amp). other processes regenerate atp. the human body recycles its own body weight equivalent in atp each day. it is also a precursor to dna and rna, and is used as a coenzyme. adenosine-5'-triphosphate names iupac name adenosine 5′-(tetrahydrogen triphosphate) systematic iupac name o1- tetrahydrogen triphosphate identifiers cas number 56-65-5 (free acid) y34369-07-8 (disodium salt hydrate) n 3d model (jsmol) interactive imageinteractive image chebi chebi:15422 y chembl chembl14249 y chemspider 5742 y drugbank db00171 y echa infocard 100.000.258 iuphar/bps 1713 kegg c00002 y pubchem cid 5957 unii 8l70q75fxe y comptox dashboard (epa) dtxsid6022559 inchi inchi=1s/c10h16n5o13p3/c11-8-5-9(13-2-12-8)15(3-14-5)10-7(17)6(16)4(26-10)1-25-30(21,22)28-31(23,24)27-29(18,19)20/h2-4,6-7,10,16-17h,1h2,(h,21,22)(h,23,24)(h2,11,12,13)(h2,18,19,20)/t4-,6-,7-,10-/m1/s1 ykey: zkhqwzamyrwxga-kqynxxcusa-n ykey: zkhqwzamyrwxga-kqynxxcubg smiles o=p(o)(o)op(=o)(o)op(=o)(o)oc3o(n2cnc1c(ncnc12)n)(o)3oc1nc(c2c(n1)n(cn2)3(((o3)cop(=o)(o)op(=o)(o)op(=o)(o)o)o)o)n properties chemical formula c10h16n5o13p3 molar mass 507.18 g/mol density 1.04 g/cm3 (disodium salt) melting point 187 °c (369 °f; 460 k) disodium salt; decomposes acidity (pka) 0.9, 1.4, 3.8, 6.5 uv-vis (λmax) 259 nm absorbance ε259 = 15.4 mm−1 cm−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). y verify (what is yn ?) infobox references interactive animation of the structure of atp from the perspective of biochemistry, atp is classified as a nucleoside triphosphate, which indicates that it consists of three components: a nitrogenous base (adenine), the sugar ribose, and the triphosphate. structure atp consists of an adenine attached by the 9-nitrogen atom to the 1′ carbon atom of a sugar (ribose), which in turn is attached at the 5' carbon atom of the sugar to a triphosphate group. in its many reactions related to metabolism, the adenine and sugar groups remain unchanged, but the triphosphate is converted to di- and monophosphate, giving respectively the derivatives adp and amp. the three phosphoryl groups are labeled as alpha (α), beta (β), and, for the terminal phosphate, gamma (γ). in neutral solution, ionized atp exists mostly as atp4−, with a small proportion of atp3−. binding of metal cations to atp being polyanionic and featuring a potentially chelating polyphosphate group, atp binds metal cations with high affinity. the binding constant for mg2+ is (9554). the binding of a divalent cation, almost always magnesium, strongly affects the interaction of atp with various proteins. due to the strength of the atp-mg2+ interaction, atp exists in the cell mostly as a complex with mg2+ bonded to the phosphate oxygen centers. a second magnesium ion is critical for atp binding in the kinase domain. the presence of mg2+ regulates kinase activity. chemical properties salts of atp can be isolated as colorless solids. the cycles of synthesis and degradation of atp; 2 and 1 represent input and output of energy, respectively. atp is stable in aqueous solutions between ph 6.8 and 7.4, in the absence of catalysts. at more extreme phs, it rapidly hydrolyses to adp and phosphate. living cells maintain the ratio of atp to adp at a point ten orders of magnitude from equilibrium, with atp concentrations fivefold higher than the concentration of adp. in the context of biochemical reactions, the p-o-p bonds are frequently referred to as high-energy bonds. reactive aspects the hydrolysis of atp into adp and inorganic phosphate releases 20.5 kj/mol of enthalpy. the values of the free energy released by cleaving either a phosphate (pi) or a pyrophosphate (ppi) unit from atp at standard state concentrations of 1 mol/l at ph 7 are: atp + h2o → adp + pi δg°' = −30.5 kj/mol (−7.3 kcal/mol) atp + h2o → amp + ppi δg°' = −45.6 kj/mol (−10.9 kcal/mol) these abbreviated equations at a ph near 7 can be written more explicitly (r = adenosyl): 4− + h2o → 3− + 2− + h+ 4− + h2o → 2− + 3− + h+ at cytoplasmic conditions, where the adp/atp ratio is 10 orders of magnitude from equilibrium, the δg is around −57 kj/mol. this image shows a 360-degree rotation of a single, gas-phase magnesium-atp chelate with a charge of −2. the anion was optimized at the ub3lyp/6-311++g(d,p) theoretical level and the atomic connectivity modified by the human optimizer to reflect the probable electronic structure. production from amp and adp production, aerobic conditions a typical intracellular concentration of atp is hard to pin down, however, reports have shown there to be 1–10 μmol per gram of tissue in a variety of eukaryotes. the dephosphorylation of atp and rephosphorylation of adp and amp occur repeatedly in the course of aerobic metabolism. atp can be produced by a number of distinct cellular processes; the three main pathways in eukaryotes are (1) glycolysis, (2) the citric acid cycle/oxidative phosphorylation, and (3) beta-oxidation. the overall process of oxidizing glucose to carbon dioxide, the combination of pathways 1 and 2, known as cellular respiration, produces about 30 equivalents of atp from each molecule of glucose. atp production by a non-photosynthetic aerobic eukaryote occurs mainly in the mitochondria, which comprise nearly 25% of the volume of a typical cell. glycolysis main article: glycolysis in glycolysis, glucose and glycerol are metabolized to pyruvate. glycolysis generates two equivalents of atp through substrate phosphorylation catalyzed by two enzymes, phosphoglycerate kinase (pgk) and pyruvate kinase. two equivalents of nicotinamide adenine dinucleotide (nadh) are also produced, which can be oxidized via the electron transport chain and result in the generation of additional atp by atp synthase. the pyruvate generated as an end-product of glycolysis is a substrate for the krebs cycle. glycolysis is viewed as consisting of two phases with five steps each. in phase 1, "the preparatory phase", glucose is converted to 2 d-glyceraldehyde-3-phosphate (g3p). one atp is invested in step 1, and another atp is invested in step 3. steps 1 and 3 of glycolysis are referred to as "priming steps". in phase 2, two equivalents of g3p are converted to two pyruvates. in step 7, two atp are produced. also, in step 10, two further equivalents of atp are produced. in steps 7 and 10, atp is generated from adp. a net of two atps is formed in the glycolysis cycle. the glycolysis pathway is later associated with the citric acid cycle which produces additional equivalents of atp. regulation in glycolysis, hexokinase is directly inhibited by its product, glucose-6-phosphate, and pyruvate kinase is inhibited by atp itself. the main control point for the glycolytic pathway is phosphofructokinase (pfk), which is allosterically inhibited by high concentrations of atp and activated by high concentrations of amp. the inhibition of pfk by atp is unusual since atp is also a substrate in the reaction catalyzed by pfk; the active form of the enzyme is a tetramer that exists in two conformations, only one of which binds the second substrate fructose-6-phosphate (f6p). the protein has two binding sites for atp – the active site is accessible in either protein conformation, but atp binding to the inhibitor site stabilizes the conformation that binds f6p poorly. a number of other small molecules can compensate for the atp-induced shift in equilibrium conformation and reactivate pfk, including cyclic amp, ammonium ions, inorganic phosphate, and fructose-1,6- and -2,6-biphosphate. citric acid cycle main articles: citric acid cycle and oxidative phosphorylation in the mitochondrion, pyruvate is oxidized by the pyruvate dehydrogenase complex to the acetyl group, which is fully oxidized to carbon dioxide by the citric acid cycle (also known as the krebs cycle). every "turn" of the citric acid cycle produces two molecules of carbon dioxide, one equivalent of atp guanosine triphosphate (gtp) through substrate-level phosphorylation catalyzed by succinyl-coa synthetase, as succinyl-coa is converted to succinate, three equivalents of nadh, and one equivalent of fadh2. nadh and fadh2 are recycled (to nad+ and fad, respectively) by oxidative phosphorylation, generating additional atp. the oxidation of nadh results in the synthesis of 2–3 equivalents of atp, and the oxidation of one fadh2 yields between 1–2 equivalents of atp. the majority of cellular atp is generated by this process. although the citric acid cycle itself does not involve molecular oxygen, it is an obligately aerobic process because o2 is used to recycle the nadh and fadh2. in the absence of oxygen, the citric acid cycle ceases. the generation of atp by the mitochondrion from cytosolic nadh relies on the malate-aspartate shuttle (and to a lesser extent, the glycerol-phosphate shuttle) because the inner mitochondrial membrane is impermeable to nadh and nad+. instead of transferring the generated nadh, a malate dehydrogenase enzyme converts oxaloacetate to malate, which is translocated to the mitochondrial matrix. another malate dehydrogenase-catalyzed reaction occurs in the opposite direction, producing oxaloacetate and nadh from the newly transported malate and the mitochondrion's interior store of nad+. a transaminase converts the oxaloacetate to aspartate for transport back across the membrane and into the intermembrane space. in oxidative phosphorylation, the passage of electrons from nadh and fadh2 through the electron transport chain releases the energy to pump protons out of the mitochondrial matrix and into the intermembrane space. this pumping generates a proton motive force that is the net effect of a ph gradient and an electric potential gradient across the inner mitochondrial membrane. flow of protons down this potential gradient – that is, from the intermembrane space to the matrix – yields atp by atp synthase. three atp are produced per turn. although oxygen consumption appears fundamental for the maintenance of the proton motive force, in the event of oxygen shortage (hypoxia), intracellular acidosis (mediated by enhanced glycolytic rates and atp hydrolysis), contributes to mitochondrial membrane potential and directly drives atp synthesis. most of the atp synthesized in the mitochondria will be used for cellular processes in the cytosol; thus it must be exported from its site of synthesis in the mitochondrial matrix. atp outward movement is favored by the membrane's electrochemical potential because the cytosol has a relatively positive charge compared to the relatively negative matrix. for every atp transported out, it costs 1 h+. producing one atp costs about 3 h+. therefore, making and exporting one atp requires 4h+. the inner membrane contains an antiporter, the adp/atp translocase, which is an integral membrane protein used to exchange newly synthesized atp in the matrix for adp in the intermembrane space. this translocase is driven by the membrane potential, as it results in the movement of about 4 negative charges out across the mitochondrial membrane in exchange for 3 negative charges moved inside. however, it is also necessary to transport phosphate into the mitochondrion; the phosphate carrier moves a proton in with each phosphate, partially dissipating the proton gradient. after completing glycolysis, the citric acid cycle, the electron transport chain, and oxidative phosphorylation, approximately 30–38 atp molecules are produced per glucose. regulation the citric acid cycle is regulated mainly by the availability of key substrates, particularly the ratio of nad+ to nadh and the concentrations of calcium, inorganic phosphate, atp, adp, and amp. citrate – the ion that gives its name to the cycle – is a feedback inhibitor of citrate synthase and also inhibits pfk, providing a direct link between the regulation of the citric acid cycle and glycolysis. beta oxidation main article: beta-oxidation in the presence of air and various cofactors and enzymes, fatty acids are converted to acetyl-coa. the pathway is called beta-oxidation. each cycle of beta-oxidation shortens the fatty acid chain by two carbon atoms and produces one equivalent each of acetyl-coa, nadh, and fadh2. the acetyl-coa is metabolized by the citric acid cycle to generate atp, while the nadh and fadh2 are used by oxidative phosphorylation to generate atp. dozens of atp equivalents are generated by the beta-oxidation of a single long acyl chain. regulation in oxidative phosphorylation, the key control point is the reaction catalyzed by cytochrome c oxidase, which is regulated by the availability of its substrate – the reduced form of cytochrome c. the amount of reduced cytochrome c available is directly related to the amounts of other substrates: 1 2 nadh + cyt c ox + adp + p i ⇌ 1 2 nad + + cyt c red + atp +\ ++\rightleftharpoons +\ + which directly implies