Biology: ATP and Energy Transfer

Study Notes

ATP (Adenosine Triphosphate) is the energy currency of the cell. It is used for cellular work such as chemical, transport, and mechanical work.
ATP is composed of:
- Adenosine
- Ribose (a sugar)
- Three phosphate groups
The bonds between the phosphate groups contain lots of energy and can be broken by hydrolysis to release energy.
When the terminal phosphate bond is broken, the energy is released, and ATP becomes ADP (Adenosine Diphosphate).
The cell converts ADP to ATP by adding a phosphate group through phosphorylation.

Energy coupling is the use of an exergonic process to drive an endergonic process.
ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to another molecule.
This phosphate transfer increases said molecule's energy level.
Cells use energy coupling to perform various tasks, including:
- Transport: ATP phosphorylates transport proteins, moving solutes across membranes.
- Mechanical: ATP binds to motor proteins to fuel movement.
- Chemical: ATP provides energy for chemical reactions to occur.

Living organisms require energy from the environment.
Energy flows into an ecosystem as sunlight and leaves as heat.
Photosynthesis in chloroplasts generates organic molecules and oxygen.
The organic molecules fuel cellular respiration, a process that occurs in mitochondria.
Cellular respiration uses oxygen and organic molecules to produce ATP.
ATP is used to power most cellular work.