Overview
This lecture explains ATP's role as the main energy currency of the cell and describes how ATP hydrolysis releases and transfers energy to drive cellular processes.
ATP Structure and Function
- ATP (adenosine triphosphate) is composed of adenosine (adenine + ribose) attached to three phosphate groups (alpha, beta, gamma).
- The bonds connecting the phosphate groups, especially between the beta and gamma phosphates, are high-energy phosphoanhydride bonds.
- ATP stores potential energy that can be rapidly released for cellular work.
ATP Hydrolysis and Energy Release
- Hydrolysis of ATP (adding water) breaks a phosphate bond to form ADP (adenosine diphosphate) and inorganic phosphate (Pi), releasing energy.
- Under standard conditions, ATP hydrolysis releases 7.3 kcal/mol (30.5 kJ/mol); in cells, it releases about 14 kcal/mol (57 kJ/mol).
- The hydrolysis reaction is reversible; cells can regenerate ATP from ADP and Pi using energy from catabolic reactions.
Energy Coupling and Cellular Work
- ATP hydrolysis is coupled to endergonic (energy-consuming) reactions, making otherwise non-spontaneous processes occur.
- Phosphorylation is the process where a phosphate group is transferred from ATP to another molecule, increasing that molecule's energy.
- The sodium-potassium (Na+/K+) pump is an example: ATP phosphorylation changes the pump's conformation, allowing active ion transport.
ATP in Metabolic Pathways
- In glycolysis, ATP phosphorylates glucose to form an unstable, high-energy intermediate needed for further breakdown.
- ATP hydrolysis often drives conformational changes in target molecules, enabling subsequent metabolic reactions.
Key Terms & Definitions
- ATP (Adenosine Triphosphate) — the main energy carrier molecule in cells.
- Phosphoanhydride bond — high-energy bonds between phosphate groups in ATP.
- Hydrolysis — chemical breakdown using water; here, it splits ATP into ADP and Pi.
- Phosphorylation — addition of a phosphate group to a molecule, often activating it.
- Energy coupling — linking an exergonic (energy-releasing) reaction to drive an endergonic (energy-consuming) reaction.
Action Items / Next Steps
- Review glycolysis and the role of ATP phosphorylation in metabolism.
- Practice energy calculation problems involving ATP hydrolysis.
- Visit the recommended animation on glycolysis for visual reinforcement.