Which compound is produced when ADP combines with a phosphate group?

When ADP (adenosine diphosphate) combines with a phosphate group, it forms ATP (adenosine triphosphate). ATP is often referred to as the energy currency of the cell because it stores and provides energy necessary for many cellular processes. This reaction is essential during cellular respiration and photosynthesis, where energy storage and transfer are critical.

In this process, the addition of a phosphate group to ADP is a key step in the energy production pathway, specifically in the phosphorylation reaction. The formation of ATP from ADP and an inorganic phosphate (Pi) is a vital part of energy metabolism, allowing cells to harness energy from nutrients.

The other choices represent different compounds that do not directly result from the combination of ADP and a phosphate group. AMP (adenosine monophosphate) is produced when ATP is dephosphorylated, CP (creatine phosphate) plays a role in energy storage in muscle cells, and GTP (guanosine triphosphate) serves as another energy source in protein synthesis and other cellular processes, but none of these are produced from the direct reaction of ADP with a phosphate group.