How Does ATP Couple Reactions?
Adenosine triphosphate (ATP) serves an essential role by storing energy so it can be released on demand -- and released in a way useful to cells. Consequently, ATP plays a key part in many essential cellular processes.
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Definitions
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The Gibbs free energy of a system is the maximum amount of nonexpansion work it can do. As noted in "Chemical Principles," (Atkins and Jones, 2008), it follows from the laws of thermodynamics that a spontaneous process, i.e., a process that does not need an external source of energy, will always be one that results in a negative change in the Gibbs free energy of the system. Many important processes in cells involve a positive change in Gibbs free energy and are therefore nonspontaneous. Splitting ATP is a process associated with a negative change in Gibbs free energy; the energy released by this reaction can be used to drive the nonspontaneous process.
Function
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ATP features a chain of three phosphate groups attached to a sugar group. The third of these phosphates can break off in a reaction that involves splitting up a water molecule; this is called a hydrolytic reaction. When it occurs, the net energy of the products of the reaction is lower than the energy of the reactants, so energy is released.
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Effects
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The energy released by the hydrolysis of ATP can power other processes. For example, it can cause a structural change in the configuration of a protein or molecule, as in the case of myosin, a protein that plays an important role in muscle contractions. A wide variety of cellular processes derive the energy they need from hydrolysis of ATP.
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References
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