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Energy in ATP

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Bibliographic Entry Result
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Barnes, Sue & Helena Curtis. Biology, Fifth Edition. New York: Worth, 1989: 180-182. "In the course of the reaction, about 7 kilocalories of energy are released per mole." 29 kJ
(per mole)
Adenosine Triphosphate. Encarta. Redmond, WA: Microsoft, 1997-2000. "With the release of the end phosphate group, 7 kilocalories of energy become available for work and the ATP molecule becomes ADP." 29 kJ
(per mole)
Farabee, M.J. ATP and Biological Energy. On-Line Biology Book. Estrella Mountain Community College, 2000. "Energy is stored in the covalent bonds between phosphates, with the greatest amount of energy (approximately 7 kilocalories) in the bond between the second and third phosphate groups." 29 kJ
(per mole)
Hinkle, Peter & Richard McCarthy. "How cells make ATP." Scientific American. March 1978: 238, 104-117 "The amount of energy needed to form ATP depends on the chemical environment, but is never more than about 15 kilocalories per mole" 63 kJ
(per mole)
Campbell, Neil. Biology, Third Edition. Benjamin Cummings, 1993: 97-101. "The reaction is exergonic, and under laboratory conditions, releases 7.3 kcal of energy per mole of ATP hydrolyzed" 31 kJ
(per mole, lab)
42–50 kJ
(per mole, cell)
Bray, Dennis. Cell Movements. New York: Garland, 1992: 6. "What is this power requirement in terms of ATP molecules, the principle currency of energy in the cell? Hydrolysis of one gram mole of ATP releases about 470 kJ of useful energy; hydrolysis of a single ATP molecule, about 10−19 J." 470 kJ
(per gram mole)
10−19 J
(per molecule)

All of the biosynthesis activities of the cell, many of its transport processes and a variety of other activities require energy. Energy is defined as the capacity to do work. Adenosine Triphosphate (ATP), a molecule found in all living organisms is the immediate source of usable energy for body cells and their function. ATP is built up by the metabolism of food in cell's mitochondria. ATP is characterized as a coenzyme because the energy exchanging function of ATP and the catalytic function of enzymes are intimately connected.

ATP is made up of the nitrogenous base adenine, the five-carbon sugar ribose and three phosphate groups. Three phosphate units (triphosphate), each made up of one phosphorus atom and four oxygen atoms, are attached to the ribose. The two bonds between the three phosphate groups are relatively weak and yield their energy readily when split by enzymes. Inside a cell the ATP molecule is split at one of the high energy bonds, releasing the energy to power cellular activities. Adenosine diphosphate (ADP) and phosphorus (P) are produced in the process. With the release of the end phosphate group, 7 kilocalories (under laboratory conditions) of energy become available for work.

ATP + H2O → ADP + Phosphate

ATP needs to be regenerated continuously by the recombining of ADP and P. From the foods and beverages people eat and drink and through the process of digestion and absorption, cells break down several types of compounds to release enough energy to cause ADP and P to recombine and replenish ATP stores. These compounds are phosphocreatine (PCr), carbohydrates, fats and proteins.

ATP is the most frequent molecule that supplies energy in coupled reactions. In coupled reactions, endergonic reactions or transport processes are linked to exergonic reactions that provide a surplus of energy. This makes the entire process exergonic and able to proceed spontaneously. The covalent bonds linking the two phosphates to the rest of the molecule are easily broken, which release energy in the amount of 7 kilocalories per mole (under laboratory conditions).

Most of the energy consuming reactions in cells are powered by the conversion of ATP to ADP; they include the transmission of nerve signals, the movement of muscles, the synthesis of protein and cell division.

Amber Iqbal -- 2000