High-energy phosphate can mean one of two things: * The

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

-phosphate (phosphoanhydride/phosphoric anhydride/macroergic/

phosphagen Phosphagens, also known as macroergic compounds, are high energy storage compounds, also known as high-energy phosphate compounds, chiefly found in muscular tissue in animals. They allow a high-energy phosphate pool to be maintained in a concentr ...

) bonds formed when compounds such as

adenosine diphosphate Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound in metabolism and is essential to the flow of energy in living cells. ADP consists of three important structural components: a sugar backbon ...

(ADP) and

adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound that provides energy to drive many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Found in all known forms of ...

(ATP) are created. * The compounds that contain these bonds, which include the nucleoside diphosphates and nucleoside triphosphates, and the high-energy storage compounds of the muscle, the

s. When people speak of a high-energy phosphate pool, they speak of the total concentration of these compounds with these high-energy bonds. High-energy phosphate bonds are usually

pyrophosphate In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate (Na2H2P2O7) and tetrasodium pyrophosphate (Na4P2O7), among other ...

bonds, acid

anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...

linkages formed by taking

phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...

derivatives and dehydrating them. As a consequence, the

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

of these bonds is

exergonic An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs fr ...

under physiological conditions, releasing

Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature and pr ...

. Except for PP_i → 2 P_i, these reactions are, in general, not allowed to go uncontrolled in the human cell but are instead coupled to other processes needing energy to drive them to completion. Thus, high-energy phosphate reactions can: * provide energy to cellular processes, allowing them to run * couple processes to a particular nucleoside, allowing for regulatory control of the process * drive a reaction out of equilibrium (drive it ''to the right'') by promoting one direction of the reaction faster than the equilibrium can relax. The one exception is of value because it allows a single hydrolysis, ATP + H₂O → AMP + PP_i, to effectively supply the energy of hydrolysis of two high-energy bonds, with the hydrolysis of PP_i being allowed to go to completion in a separate reaction. The AMP is regenerated to ATP in two steps, with the equilibrium reaction ATP + AMP ↔ 2ADP, followed by regeneration of ATP by the usual means,

oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine tri ...

or other energy-producing pathways such as

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvate (). The free energy released in this process is used to form the high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide (NADH ...

. Often, high-energy phosphate bonds are denoted by the character '~'. In this "squiggle" notation, ATP becomes A-P~P~P. The squiggle notation was invented by

Fritz Albert Lipmann Fritz Albert Lipmann (; June 12, 1899 – July 24, 1986) was a German-American biochemist and a co-discoverer in 1945 of coenzyme A. For this, together with other research on coenzyme A, he was awarded the Nobel Prize in Physiology or Medicine in ...

, who first proposed ATP as the main energy transfer molecule of the cell, in 1941. Lipmann's notation emphasizes the special nature of these bonds.Lubert Stryer ''Biochemsitry'', 3rd edition, 1988. Chapter 13, p. 318 Stryer states: The term 'high energy' with respect to these bonds can be misleading because the negative free energy change is not due directly to the breaking of the bonds themselves. The breaking of these bonds, like the breaking of most bonds, is

endergonic In chemical thermodynamics, an endergonic reaction (; also called a heat absorbing nonspontaneous reaction or an unfavorable reaction) is a chemical reaction in which the standard change in free energy is positive, and an additional driving fo ...

and consumes energy rather than releasing it. The negative free energy change comes instead from the fact that the bonds formed after hydrolysis - or the

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

of a residue by ATP - are lower in energy than the bonds present before hydrolysis. (This includes ''all'' of the bonds involved in the reaction, not just the phosphate bonds themselves). This effect is due to a number of factors including increased

resonance stabilization In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...

and

solvation Solvation (or dissolution) describes the interaction of a solvent with dissolved molecules. Both ionized and uncharged molecules interact strongly with a solvent, and the strength and nature of this interaction influence many properties of the ...

of the products relative to the reactants.

References

Further reading