The energy released by the hydrolysis of ATP is _ .
equal to -57 ?kcal/m
providing energy to coupled reactions
harnessed as heat energy by the cell to perform work
primarily stored between the alpha and beta phosphates
The correct answer and explanation is :
The energy released by the hydrolysis of ATP is primarily utilized to drive coupled reactions within the cell. This energy is harnessed to perform various cellular tasks, such as muscle contraction, active transport, and biosynthetic processes.
Adenosine triphosphate (ATP) consists of an adenosine molecule bound to three phosphate groups. The bonds connecting these phosphate groups, known as phosphoanhydride bonds, are high-energy bonds. When ATP undergoes hydrolysis—a reaction with water that cleaves one of these bonds—it produces adenosine diphosphate (ADP) and an inorganic phosphate (Pi), releasing energy in the process. The standard free energy change (ΔG°’) for ATP hydrolysis is approximately -7.3 kcal/mol (-30.5 kJ/mol). However, under typical cellular conditions, this value is closer to -14 kcal/mol (-57 kJ/mol), indicating a more substantial energy release in vivo.
This released energy is not merely dissipated as heat; rather, it is efficiently utilized to power endergonic (energy-requiring) reactions through a mechanism known as energy coupling. In energy coupling, the exergonic (energy-releasing) hydrolysis of ATP is linked with endergonic processes, thereby driving them forward. For example, the sodium-potassium pump, which maintains cellular ion gradients, relies on ATP hydrolysis to function. The energy from ATP hydrolysis induces conformational changes in the pump protein, enabling it to transport sodium and potassium ions against their concentration gradients.
Regarding the other options:
- Equal to -57 kcal/mol: While the standard free energy change is -7.3 kcal/mol, under cellular conditions, it is approximately -14 kcal/mol.
- Harnessed as heat energy by the cell to perform work: Although some energy is lost as heat, the primary function of ATP hydrolysis is to provide energy for biochemical work, not to generate heat.
- Primarily stored between the alpha and beta phosphates: The high-energy bonds are located between the beta and gamma phosphates, not between the alpha and beta.
Therefore, the correct statement is that the energy released by ATP hydrolysis is utilized to drive coupled reactions, facilitating various energy-requiring processes within the cell.