ATP hydrolysis is the chemical reaction in which adenosine triphosphate (ATP) is broken down by water into adenosine diphosphate (ADP) and an inorganic phosphate (Pi), releasing energy that is used to power various biological processes.
Chemical Reaction:
ATP+H2O→ADP+Pi+Energy\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}ATP+H2O→ADP+Pi+Energy
- ATP = Adenosine triphosphate
- ADP = Adenosine diphosphate
- Pi = Inorganic phosphate
- ΔG (free energy change) ≈ −7.3 kcal/mol under standard conditions (more negative in cells)
How It Works:
- ATP contains three phosphate groups linked by high-energy phosphoanhydride bonds.
- The bond between the second and third phosphate is most often hydrolyzed.
- Hydrolysis breaks this bond by adding a water molecule.
- This releases energy, which is then harnessed by enzymes or proteins (e.g., motor proteins, pumps, kinases) to do work.
Biological Significance:
| Process | Role of ATP Hydrolysis |
|---|---|
| Muscle contraction | Powers myosin movement along actin filaments |
| Active transport | Drives ion pumps (e.g., Na⁺/K⁺-ATPase) to move ions across membranes against their gradients |
| Biosynthesis | Provides energy for building macromolecules (DNA, RNA, proteins) |
| Signal transduction | Activates enzymes and signaling proteins via phosphorylation |
| Cell motility | Fuels cytoskeletal changes and movement |
Enzymes That Use ATP Hydrolysis:
- ATPases: General term for enzymes that hydrolyze ATP.
- Kinases: Transfer phosphate groups from ATP to other molecules.
- Motor proteins: Myosin, kinesin, dynein use ATP hydrolysis to move.
- Transporters: Like ABC transporters and ion pumps.
ATP Hydrolysis in Energy Coupling:
- In cells, energy-releasing reactions (like ATP hydrolysis) are coupled to energy-requiring processes so they can proceed.
- For example:
Glucose + ATP → Glucose-6-phosphate + ADP
This traps glucose inside the cell and begins glycolysis.
Summary Table:
| Feature | Description |
|---|---|
| Reaction | ATP + H₂O → ADP + Pi + energy |
| Energy Released | ~7.3 kcal/mol (standard); more under cellular conditions |
| Function | Powers biochemical processes |
| Common Enzymes | ATPases, kinases, motor proteins |
| Key Uses | Muscle contraction, active transport, biosynthesis, signaling |