Which nucleotide is primarily involved in energy metabolism and is used to store energy?

Adenosine Triphosphate (ATP) is the primary nucleotide involved in energy metabolism and is essential for storing and transferring energy within cells. ATP is often referred to as the "energy currency" of the cell because it powers many biological processes. When ATP is hydrolyzed, it releases energy that can be used for various cellular activities such as muscle contraction, active transport across cell membranes, and synthesis of macromolecules.

ATP consists of adenosine, which is made up of an adenine nucleotide and a ribose sugar, along with three phosphate groups. The high-energy bonds between the phosphate groups, particularly the bond between the second and third phosphate, release significant energy when broken. This makes ATP an ideal molecule for energy transfer, as it can quickly release energy when needed and can also be regenerated from ADP (adenosine diphosphate) and inorganic phosphate in metabolic processes.

While cyclic AMP, NADH, and GTP also play important roles in cellular functions—such as signaling, electron transport, and energy transfer, respectively—they do not serve as the primary energy currency like ATP does. Thus, ATP is distinctly recognized for its crucial function in energy metabolism in biological systems.