ISSA Nutritionist Practice Exam

How is energy stored in cells primarily?

1. As glycogen

2. As triglycerides

3. As ATP

4. As proteins

The correct answer is: As ATP

Energy is primarily stored in cells as ATP, or adenosine triphosphate. ATP is a high-energy molecule that serves as a universal energy currency within biological systems. Cells utilize ATP to fuel various biochemical processes, including muscle contraction, nerve impulse propagation, and biosynthesis. The ATP molecule consists of adenine, ribose, and three phosphate groups, and when one of the phosphate bonds is broken through hydrolysis, a significant amount of energy is released, which can be harnessed for cellular activities. While glycogen and triglycerides serve as forms of stored energy in the body, they require conversion into a usable form of energy before they can be utilized by cells; for instance, glycogen must be broken down into glucose, and triglycerides must be converted into fatty acids. Proteins can also contribute to energy production if necessary, but their primary role is structural and functional within cells rather than serving as a primary energy source. ATP directly fulfills the immediate energy requirements of cells, making it the most relevant choice when considering how energy is stored for immediate and efficient use.