Energy coupling
Using an energy-releasing reaction to drive an energy-needing one. In cells, ATP breakdown is usually the releasing reaction.
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Analogy
Using a falling weight to lift another weight.
In practice
Cells pair ATP breakdown with building a bond, so the combined reaction has a negative delta G and goes ahead.
Practice
Flashcards
- How do cells make an energy-needing reaction go ahead?By coupling it to ATP breakdown so the overall delta G is negative.
Interview questions
- Describe how ATP lets a cell carry out reactions that would not happen by themselves.
- Hydrolysis has large negative delta G
- Coupling makes overall delta G negative
- ATP is regenerated from ADP
Questions people ask
How does ATP couple to another reaction in practice?
Often the end phosphate of ATP is transferred to the other molecule, making it unstable and more reactive. The enzyme holds both together. This phosphorylation changes the shape or energy of the target, so it can then do work, such as a pump changing shape to carry an ion.
Is any energy lost in coupled reactions?
Yes. No transfer is perfect, and some energy is always released as heat. Cells capture about 40 percent of the energy in glucose as ATP during respiration. The rest becomes heat, which is why warm-blooded animals stay warm, and why large crowds heat up a room.