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Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important
organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds compr ...
in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining ...

metabolism
and is essential to the flow of energy in living
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
. ADP consists of three important structural components: a
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosacc ...

sugar
backbone attached to
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
and two
phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

phosphate
groups bonded to the 5 carbon atom of
ribose Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 and the linear-form composition H−(C=O)−(CHOH)4−H. The naturally-occurring form, , is a component of the ribonucleotides from which RNA is built, and so this compoun ...

ribose
. The diphosphate group of ADP is attached to the 5’ carbon of the sugar backbone, while the adenine attaches to the 1’ carbon. ADP can be interconverted to
adenosine triphosphate Adenosine triphosphate (ATP) is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properti ...

adenosine triphosphate
(ATP) and
adenosine monophosphate Adenosine is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...
(AMP). ATP contains one more phosphate group than does ADP. AMP contains one fewer phosphate group. Energy transfer used by all living things is a result of
dephosphorylation In biochemistry Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-Euro ...
of ATP by enzymes known as
ATPase ATPases (, adenylpyrophosphatase, ATP monophosphatase, triphosphatase, SV40 T-antigen, adenosine 5'-triphosphatase, ATP hydrolase, complex V (mitochondrial electron transport), (Ca2+ + Mg2+)-ATPase, HCO3−-ATPase, adenosine triphosphatase) are ...
s. The cleavage of a phosphate group from ATP results in the coupling of energy to metabolic reactions and a by-product of ADP. ATP is continually reformed from lower-energy species ADP and AMP. The biosynthesis of ATP is achieved throughout processes such as
substrate-level phosphorylation Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armeni ...
,
oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), c ...

oxidative phosphorylation
, and
photophosphorylationImage:Thylakoid membrane 3.svg, 300px, The scientist Charles Barnes first used the word 'photosynthesis' in 1893. This word is taken from two Greek words, which means light and which in chemistry means making a substance by combining simpler sub ...
, all of which facilitate the addition of a phosphate group to ADP.


Bioenergetics

ADP cycling supplies the
energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regula ...

energy
needed to do work in a biological system, the
thermodynamic Thermodynamics is a branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related ent ...
process of transferring energy from one source to another. There are two types of energy:
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...

potential energy
and
kinetic energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
. Potential energy can be thought of as stored energy, or usable energy that is available to do work. Kinetic energy is the energy of an object as a result of its motion. The significance of ATP is in its ability to store potential energy within the phosphate bonds. The energy stored between these bonds can then be transferred to do work. For example, the transfer of energy from ATP to the protein
myosin Myosins () are a superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilie ...

myosin
causes a conformational change when connecting to
actin Actin is a protein family, family of Globular protein, globular multi-functional proteins that form microfilaments. It is found in essentially all Eukaryote, eukaryotic cells, where it may be present at a concentration of over 100 Micromolar, μ ...
during
muscle contraction Muscle contraction is the activation of tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches ...

muscle contraction
. It takes multiple reactions between myosin and actin to effectively produce one muscle contraction, and, therefore, the availability of large amounts of ATP is required to produce each muscle contraction. For this reason, biological processes have evolved to produce efficient ways to replenish the potential energy of ATP from ADP. Breaking one of ATP's phosphorus bonds generates approximately 30.5
kilojoule The joule ( ; symbol: J) is a derived unit of energy In physics, energy is the physical quantity, quantitative physical property, property that must be #Energy transfer, transferred to a physical body, body or physical system to perform W ...
s per
mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpidae ...
of ATP (7.3
kcal The calorie is a unit of energy As energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...
). ADP can be converted, or powered back to ATP through the process of releasing the chemical energy available in food; in humans, this is constantly performed via
aerobic respiration Aerobic means "requiring Earth's atmosphere, air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Cellular respiration#Aerobic r ...
in the
mitochondria A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, i ...

mitochondria
. Plants use
photosynthetic Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...
pathways to convert and store energy from sunlight, also conversion of ADP to ATP. Animals use the energy released in the breakdown of glucose and other molecules to convert ADP to ATP, which can then be used to fuel necessary growth and cell maintenance.


Cellular respiration


Catabolism

The ten-step
catabolic Catabolism () is the set of metabolic pathways that breaks down molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an ...
pathway of
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
is the initial phase of free-energy release in the breakdown of
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
and can be split into two phases, the preparatory phase and payoff phase. ADP and
phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

phosphate
are needed as precursors to synthesize ATP in the payoff reactions of the
TCA cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set o ...

TCA cycle
and
oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), c ...

oxidative phosphorylation
mechanism. During the payoff phase of glycolysis, the enzymes phosphoglycerate kinase and pyruvate kinase facilitate the addition of a phosphate group to ADP by way of
substrate-level phosphorylation Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP ATP may refer to: Companies and organizations * Association of Tennis Professionals * American Technical Publishers * ', a Danish pension * Armeni ...
.


Glycolysis

Glycolysis is performed by all living organisms and consists of 10 steps. The net reaction for the overall process of
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
is: :Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 ATP + 2 NADH + 2 H2O Steps 1 and 3 require the input of energy derived from the hydrolysis of ATP to ADP and Pi (inorganic phosphate), whereas steps 7 and 10 require the input of ADP, each yielding ATP. The
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
s necessary to break down glucose are found in the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
, the viscous fluid that fills living cells, where the glycolytic reactions take place.


Citric acid cycle

The
citric acid cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reactions to release stored energy through the redox, oxidation of acetyl-CoA derived from carbohydra ...

citric acid cycle
, also known as the Krebs cycle or the TCA (tricarboxylic acid) cycle is an 8-step process that takes the pyruvate generated by glycolysis and generates 4 NADH, FADH2, and GTP, which is further converted to ATP. It is only in step 5, where GTP is generated, by succinyl-CoA synthetase, and then converted to ATP, that ADP is used (GTP + ADP → GDP + ATP).


Oxidative phosphorylation

Oxidative phosphorylation Oxidative phosphorylation (UK , US ) or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), c ...

Oxidative phosphorylation
produces 26 of the 30 equivalents of ATP generated in cellular respiration by transferring electrons from NADH or FADH2 to through electron carriers. The energy released when electrons are passed from higher-energy NADH or FADH2 to the lower-energy O2 is required to phosphorylate ADP and once again generate ATP. It is this energy coupling and phosphorylation of ADP to ATP that gives the electron transport chain the name oxidative phosphorylation.


Mitochondrial ATP synthase complex

During the initial phases of
glycolysis Glycolysis is the metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of on ...

glycolysis
and the
TCA cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set o ...

TCA cycle
, cofactors such as
NAD+ Nicotinamide adenine dinucleotide (NAD) is a Cofactor (biochemistry), coenzyme central to metabolism. Found in all living cell (biology), cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphat ...

NAD+
donate and accept electrons that aid in the
electron transport chain An electron transport chain (ETC) is a series of protein complex A protein complex or multiprotein complex is a group of two or more associated polypeptide chain Peptides (from Greek language Greek (modern , romanized: ''Elliniká'', Anc ...

electron transport chain
's ability to produce a proton gradient across the inner mitochondrial membrane. The ATP synthase complex exists within the mitochondrial membrane (FO portion) and protrudes into the matrix (F1 portion). The energy derived as a result of the chemical gradient is then used to synthesize ATP by coupling the reaction of inorganic phosphate to ADP in the active site of the
ATP synthase ATP synthase is a protein that catalyzes the formation of the energy storage molecule adenosine triphosphate (ATP) using adenosine diphosphate (ADP) and inorganic phosphate (Pi). It is classified under ligases as it changes ADP by the formation of ...

ATP synthase
enzyme; the equation for this can be written as ADP + Pi → ATP.


Blood platelet activation

Under normal conditions, small disk-shape
platelet Platelets, also called thrombocytes (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...

platelet
s circulate in the blood freely and without interaction with one another. ADP is stored in inside
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
platelet Platelets, also called thrombocytes (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...

platelet
s and is released upon platelet activation. ADP interacts with a family of ADP receptors found on platelets (P2Y1,
P2Y12 P2Y12 is a chemoreceptor for adenosine diphosphate Adenosine diphosphate (ADP), also known as adenosine pyrophosphate (APP), is an important organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are ...
, and P2X1), which leads to platelet activation. * P2Y1 receptors initiate platelet aggregation and shape change as a result of interactions with ADP. * P2Y12 receptors further amplify the response to ADP and draw forth the completion of aggregation. ADP in the blood is converted to
adenosine Adenosine is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, cate ...

adenosine
by the action of ecto-ADPases, inhibiting further platelet activation via
adenosine receptor The adenosine receptors (or P1 receptors) are a class of purinergic G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine re ...
s.


See also

*
Nucleoside Nucleosides are s that can be thought of as s without a . A nucleoside consists simply of a (also termed a nitrogenous base) and a five-carbon sugar ( or 2'-deoxyribose) whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and ...

Nucleoside
*
Nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

Nucleotide
*
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
*
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
*
OligonucleotideOligonucleotides are short DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of line ...
* Apyrase *
Phosphate In chemistry, a phosphate is an anion, salt (chemistry), salt, functional group or ester derived from a phosphoric acids and phosphates, phosphoric acid. It most commonly means orthophosphate, a derivative of phosphoric acid, orthophosphoric a ...

Phosphate


References

{{DEFAULTSORT:Adenosine phosphate2 Adenosine receptor agonists Neurotransmitters Nucleotides Cellular respiration Phosphate esters Purines Purinergic signalling Pyrophosphates