Key Concepts
* Exergonic Reactions: Release energy. They have a negative change in Gibbs free energy (ΔG < 0). Think of them like a downhill reaction.
* Endergonic Reactions: Require energy input to occur. They have a positive change in Gibbs free energy (ΔG > 0). Think of them like an uphill reaction.
* ATP (Adenosine Triphosphate): The primary energy currency of cells. It stores energy in its phosphate bonds.
The Coupling
Exergonic reactions and endergonic reactions are often coupled together in a process called energy coupling. This is how cells power their essential functions.
1. Exergonic reactions provide energy: The energy released from an exergonic reaction is used to drive an endergonic reaction.
2. ATP is the intermediary: ATP is the molecule that transfers energy between exergonic and endergonic reactions.
* Exergonic reactions generate ATP by releasing energy.
* Endergonic reactions utilize the energy stored in ATP to proceed.
Example: Cellular Respiration and Photosynthesis
* Cellular Respiration: The breakdown of glucose (an exergonic reaction) releases energy that is used to generate ATP. This ATP is then used to power many cellular processes, like muscle contraction and protein synthesis (endergonic reactions).
* Photosynthesis: The conversion of sunlight energy into chemical energy (in the form of glucose) is an endergonic reaction. This process is powered by the ATP generated from the exergonic reaction of splitting water.
Regeneration of ATP
ATP is constantly being used and regenerated in cells. The energy released from exergonic reactions is used to add a phosphate group to ADP (adenosine diphosphate), creating ATP. This process is called phosphorylation.
Summary
* Exergonic reactions are like energy sources; they release energy that can be captured.
* Endergonic reactions are like energy sinks; they require energy to proceed.
* ATP is the energy currency that allows the energy released from exergonic reactions to be used to power endergonic reactions.
* The constant regeneration of ATP through phosphorylation ensures a continuous energy supply for the cell.
