Overview
This section explains ATP's central role as the cell's energy currency and describes how ATP hydrolysis releases energy to power cellular processes.
Structure and Role of ATP
- ATP (adenosine triphosphate) is the main energy currency of the cell.
- ATP consists of adenosine (adenine + ribose) and three phosphate groups: alpha, beta, and gamma.
- Energy is stored in high-energy phosphoanhydride bonds between the phosphate groups.
- The breaking of these bonds releases energy that cells use for various functions.
ATP Hydrolysis and Energy Release
- Hydrolysis of ATP (ATP + H₂O → ADP + Pᵢ + free energy) releases energy for cellular work.
- The hydrolysis reaction converts ATP to ADP (adenosine diphosphate) and inorganic phosphate (Pᵢ).
- This process is reversible; ATP can be regenerated from ADP and Pᵢ when energy is available.
- Standard free energy change (ΔG) for ATP hydrolysis is -7.3 kcal/mol; in cells, ΔG is about -14 kcal/mol.
Energy Coupling in Cellular Processes
- Cells couple ATP hydrolysis (exergonic) to endergonic reactions to drive processes requiring energy.
- The sodium-potassium (Na⁺/K⁺) pump uses ATP hydrolysis to export Na⁺ and import K⁺ against their concentration gradients.
- During energy coupling, ATP's terminal phosphate group is transferred to another molecule—a process called phosphorylation.
- Phosphorylation changes the shape and function of target molecules, enabling cellular work.
ATP in Metabolic Reactions
- ATP is required in glycolysis to phosphorylate glucose, forming unstable intermediates necessary for further steps.
- The energy released from ATP hydrolysis powers these conformational and chemical changes in metabolic pathways.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — Cellular molecule that stores and transfers energy for cellular work.
- Hydrolysis — Chemical reaction involving breakdown by water; in ATP, releases ADP, phosphate, and energy.
- Phosphorylation — Addition of a phosphate group to a molecule, often altering its activity or function.
- Energy Coupling — Linking an exergonic reaction (like ATP hydrolysis) to drive an endergonic reaction.
- Na⁺/K⁺ Pump — Membrane protein that uses ATP to move sodium and potassium ions against their gradients.
Action Items / Next Steps
- Review how ATP hydrolysis is coupled to drive cellular processes.
- Watch an animation of glycolysis and ATP use at the suggested site.