What is the chemical energy used within cells for metabolism?

The chemical energy used within cells for metabolism is Adenosine Triphosphate (ATP). ATP is often referred to as the energy currency of the cell because it provides the necessary energy for various cellular processes. When a cell needs energy for metabolic reactions, it breaks down ATP into adenosine diphosphate (ADP) and an inorganic phosphate, releasing energy that can be harnessed for functions such as muscle contraction, nerve impulse propagation, and biosynthesis of macromolecules.

While glucose plays a critical role in the production of ATP, particularly in cellular respiration, it is not utilized directly as the energy source within cells. NADH is an important electron carrier in the metabolic pathways such as glycolysis and the citric acid cycle, but it serves to transfer electrons rather than being the direct source of energy. Glycogen is a storage form of glucose, and while it can be converted into glucose for ATP production, it is not the immediate energy currency itself. Therefore, ATP is uniquely suited as the direct chemical energy source required for metabolic processes in the cell.