The major energy carrier molecule in cells is adenosine triphosphate (ATP). Adenosine triphosphate is a nucleoside triphosphate that stores all of the energy inside of cells.
Energy comes from the enzymatic breakdown of food and is transformed into carbohydrates, glycogen and fat. Any time energy is needed for the cell, it is converted from storage molecules into ATP, which then travels to where it is needed inside of the cell. NADH (Nicotinamide adenine dinucleotide) is the other energy carrier inside of cells. According to BioMedia Associates, ATP is the universal and rechargeable energy carrier for most cells. ATP is also a coenzyme.