Adenosine triphosphate (ATP) is a reservoir of potential chemical energy and an energy currency, mediating most energy coupling in cells.

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        Adenosine triphosphate (ATP) is a reservoir of potential chemical energy and an energy currency, mediating most energy coupling in cells. ATP and its derivatives are involved heavily in metabolism, however they have other functions such as being allosteric inhibitors and effectors, as well in hormonal response( cyclic AMP). ATP was first isolated from mammalian muscle; it has since been shown to occur in all types of cell, at concentrations varying between 0.5 and 2.5 mg/cm3  . ATP plays such an important role in an organism that without its existence, systems would probably fail. Thus its continuous production is necessary in order to main survival. 

        The structure of ATP is linked very closely to its function, specifically its triphosphate tail, which is the chemical equivalent of a loaded spring. Adenosine triphosphate is a nucleotide consisting of an organic base (adenine), a five carbon sugar (ribose) and a chain sequence of three phosphate groups linked together.  The adenosine part of the molecule acts like a ‘handle”-it has a shape which can be recognized by highly specific enzymes. When only one phosphoryl group is added to the ribose sugar and base adenine, the nucleotide adenosine monophosphate (AMP) is formed; adding a second phosphoyrl group makes adenosine diphosphate (ADP); and adding a third makes ATP. Each compound can be made from the next smaller one plus a phosphate, H3PO4 (also known as inorganic phosphate) with the removal of water. This is an endergonic reaction and free energy is stored in ATP during the process. This energy is then retrieved when ATP is used to phosphorylate some other compound. When this happens the nucleotide loses a phosphate group, however there are some reactions in which both the terminal phosphates are removed together as pyrophosphate, H2P4O7.

        ATP is extremely important in cell metabolism. A large amount of energy is required in many cell reactions such as to couple together sugar residues to make a cellulose molecule or to couple together the hundreds of amino acid residues to make a protein molecule. These processes, like many others in metabolism are endergonic.  Endergonic reactions are driven by coupling them to exergonic reactions. ATP has the function of linking endergonic(energy-demanding) reactions with exergonic(energy yielding) reactions.

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        Organic compounds of which organisms are made have more free energy and more reduced than are the raw materials that the organism takes in. Reduced organic compounds are also energy rich materials that heterotrophs use as energy sources. The general problem an organism faces is the need to make one of these more energetic compounds by driving a reaction in the uphill or endergonic direction. This is done by coupling such reactions to exergonic reactions that release somewhat more energy, so the two reactions taken together still have the decrease in free energy. Coupling generally occurs through a group transfer ...

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