Adenosine triphosphate

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For other uses of the initials ATP, see ATP (disambiguation)

Adenosine triphosphate
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Adenosine 5'-triphosphate (ATP) is the nucleotide known in biochemistry as the "molecular currency" of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ATP also plays an important role in the synthesis of nucleic acids. ATP molecules are also used to store the usable energy that plants convert in cellular respiration. In signal transduction pathways, ATP is used to provide the phosphate for the protein-kinase reactions.

Contents 1 Chemical properties 2 Synthesis 3 Function 4 ATP in the human body 5 Other uses 6 See also 7 External link

Chemical properties

Chemically, ATP consists of adenosine and three phosphate groups(triphosphate). The phosphoryl groups starting with that on AMP are referred to as the alpha (α), beta (β), and gamma (γ) phosphates.

Synthesis

Image:Atp space filling ray trace.jpg ATP can be produced by various cellular processes — under aerobic conditions, the synthesis occurs in mitochondria during the oxidative phosphorylation and is catalyzed by ATP synthase or to a lesser degree; under anaerobic conditions, this is done through substrate phosphorylation catalyzed by two family of enzymes: PGK and Pyruvate kinase.

ATP is also synthesized through several so called "replenishment" reactions catalyzed by the enzyme families of NDKs (Nucleoside diphosphate kinases), which use other nucleoside triphosphates as a high-energy phosphate donor, and the ATP:guanido-phosphotransferase family, which uses creatine.

ADP + GTP <math>\to</math> ATP + GDP

In plants ATP is synthesized in chloroplasts by photosynthesis.

The main fuels for ATP synthesis are Glc and FAs. Initially Glc is broken down into pyruvate in the cytosol. Two molecules of ATP are generated for each molecule of Glc. The terminal stages of ATP synthesis are carried out in the mitochondrion and can generate up to 36 ATP, which is 39% energy efficiency.

Function

ATP energy is released when hydrolysis of the phosphate-phosphate bonds is carried out. This energy can be used by a variety of enzymes, motor proteins, and transport proteins to carry out the work of the cell. Also, the hydrolysis yields free inorganic P_i and ADP, which can be broken down further to another P_i and AMP. ATP can also be broken down to AMP directly, with the formation of PP_i. This last reaction has the advantage of being an effectively irreversible process in aqueous solution.

ATP in the human body

The total quantity of ATP in the human body is about 0.1 mole. The energy used by human cells requires the hydrolysis of 200 to 300 moles of ATP daily. This means that each ATP molecule is recycled 2000 to 3000 times during a single day. ATP cannot be stored, hence its consumption must closely follow its synthesis. On a per hour basis, 1 kilogram of ATP is created, processed and then recycled in the body.

Other uses

There is talk of using ATP as a power source for nanotechnology and implants. Artificial pacemakers could become independent of batteries.

See also

• Adenosine diphosphate (ADP)
• Adenosine monophosphate (AMP)
• Cyclic adenosine monophosphate (cAMP)
• ATPases
• ATP hydrolysis
• Citric acid cycle (also called the Krebs cycle)
• Phosphagen
• Thioesters are related to ATP
• ATP thermochemistry
• Nucleotide exchange factor

External link

• ATP and biological energy