Which molecule acts as the primary energy carrier in cells?

ATP, or adenosine triphosphate, is recognized as the primary energy carrier in cells due to its unique structure and function. It consists of adenosine and three phosphate groups. The bonds between these phosphate groups, particularly the terminal phosphate bond, are high-energy bonds. When ATP is hydrolyzed (broken down), it releases energy that can be utilized for various cellular processes, including muscle contractions, active transport across membranes, and biosynthetic reactions.

The availability of ATP allows for rapid and efficient energy transfer, making it essential for maintaining cellular functions. While other molecules like NADPH play roles in energy transfer, specifically in the context of photosynthesis and redox reactions, they do not serve the same broad primary energy-carrying function as ATP. Dismissing carbohydrate molecules like glucose, although they are important energy sources, they must first be metabolized to produce ATP before the energy can be harnessed for cellular work. Thus, ATP's direct involvement in energy transfer and usage in metabolic pathways solidifies its role as the primary energy carrier in cells.