AP BIOLOGY

Detailed explanation-1: -If a cell needs to spend energy to accomplish a task, the ATP molecule splits off one of its three phosphates, becoming ADP (Adenosine di-phosphate) + phosphate. The energy holding that phosphate molecule is now released and available to do work for the cell.

Detailed explanation-2: -Removing or adding one phosphate group interconverts ATP to ADP or ADP to AMP. Breaking one phosphoanhydride bond releases 7.3 kcal/mol of energy.

Detailed explanation-3: -Substrate Phosphorylation A phosphate group is removed from an intermediate reactant in the pathway, and the free energy of the reaction is used to add the third phosphate to an available ADP molecule, producing ATP (Figure 2). This very direct method of phosphorylation is called substrate-level phosphorylation.

Detailed explanation-4: -Although cells continuously break down ATP to obtain energy, ATP also is constantly being synthesized from ADP and phosphate through the processes of cellular respiration. Most of the ATP in cells is produced by the enzyme ATP synthase, which converts ADP and phosphate to ATP.