ADP gets converted to ATP in the inner membranes of mitochondria that are located in the cytoplasm of a cell. This conversion of ADP to ATP is known as chemiosmotic phosphorylation.

During chemiosmotic phosphorylation, a high phosphate group is added to ADP, which is a low-energy molecule. The addition of the phosphate group converts ADP to ATP, a high-energy molecule that stores energy for use when necessary.