D. Reaction Coupling
➢ ATP consists of a molecule of adenosine bonded to 3 phosphates
- Carries enormous amount of energy within phosphate bonds
➢ When a cell needs energy, it splits off the 3rd phosphate, forming adenosine diphosphate (ADP) and one loose phosphate $(P_i)$ in the process
- $ \text{ATP→ADP + Pi + energy}$
➢ ATP is relatively neat and easy to form
➢ Sources
- Cellular respiration
■ Sugar turned into ATP
● In plants, sugar is made by photosynthesis
● In animals, sugar is taken from food consumed