Move energy in manageable steps
Cells do not release and use all of a fuel molecule’s chemical energy in one step. Metabolic pathways transfer energy through controlled reactions, and ATP acts as a short-term carrier that connects energy-releasing reactions to jobs that require energy.
When ATP reacts with water in a process called hydrolysis, it forms ADP and a phosphate group. Cells couple, or connect, this energy-releasing reaction to cellular work, often by transferring the phosphate or changing a protein’s shape.
Recharge the carrier
ATP is continually recycled rather than stored unchanged as a permanent battery. Adding a phosphate back to ADP requires an energy input. Cellular respiration transfers energy from fuel molecules to help rebuild ATP, and photosynthetic cells can also make ATP while capturing light energy.
This cycle helps a cell match energy supply with demand. The cell uses ATP for work such as active transport and movement, produces ADP and phosphate, and then uses energy-yielding pathways to regenerate ATP.
Remember these ideas
Key ideas
- ATP is a short-term, transferable energy carrier rather than a long-term food store.
- ATP hydrolysis forms ADP and phosphate. When a cell connects that reaction to cellular work, the released energy can help drive the work.
- Rebuilding ATP from ADP and phosphate requires an energy input.
- Cells continually connect energy-yielding pathways with transport, movement, and molecule-building.
Make the reasoning visible
Trace the energy · an ATP-powered membrane pump
- 1
The pump moves ions against their electrochemical gradients, so the transport requires energy.
- 2
The pump connects ATP hydrolysis to a change in its protein shape; ATP becomes ADP and phosphate.
- 3
That shape change moves the ions across the membrane against their gradient.
- 4
Energy-yielding reactions later help rebuild ATP from ADP and phosphate so the cycle can continue.
Try the next step
Follow one ATP cycle
A motor protein uses ATP while moving a vesicle inside a cell. What happens to the ATP, and how can the cell restore its ATP supply?
Why is “recyclable energy carrier” more accurate than describing ATP as the original source of all cellular energy?