The energy released from molecules to power cellular functions is primarily through the hydrolysis of adenosine triphosphate (ATP). ATP serves as the primary energy currency of the cell. Here are the key processes:
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Hydrolysis of ATP: When ATP is hydrolyzed, it breaks down into adenosine diphosphate (ADP) and an inorganic phosphate (Pi), a reaction that releases energy. The equation for this reaction is: \[ ATP \rightarrow ADP + Pi + \text{Energy} \] This energy is harnessed by cells to perform various functions, such as muscle contraction, active transport, and biosynthesis.
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Phosphorylation: When ADP gains a phosphate group, it can be converted back into ATP. This process is called phosphorylation and typically occurs during cellular respiration or photosynthesis. The reaction can be summarized as: \[ ADP + Pi + \text{Energy} \rightarrow ATP \] This conversion is essential for regenerating ATP in the cell, allowing for a continuous supply of energy.
Thus, the correct statement reflecting this process in your options is:
- An ADP molecule adds a phosphate group, forming ATP.
The other statements involve slightly different or incorrect descriptions of the energy transfer processes involving ATP and ADP. To summarize, ATP releases energy when it is converted to ADP by releasing a phosphate group, and energy is required to regenerate ATP from ADP by adding a phosphate group.
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