Endergonic reaction

File:Endergonic Reaction.svg

Diagram of an endergonic reaction

An endergonic reaction is a type of chemical reaction in which the standard change in free energy is positive, and energy is absorbed from the surroundings. This is in contrast to an exergonic reaction, where energy is released. Endergonic reactions are non-spontaneous, meaning they require an input of energy to proceed.

Thermodynamics

In thermodynamic terms, an endergonic reaction is characterized by a positive change in Gibbs free energy (_G > 0). This indicates that the products of the reaction have higher energy than the reactants, and thus, energy must be supplied for the reaction to occur. The equation for Gibbs free energy is:

_G = _H - T_S

where _H is the change in enthalpy, T is the temperature in Kelvin, and _S is the change in entropy. For an endergonic reaction, the enthalpy change is often positive, and the entropy change can be negative or positive, but the overall _G remains positive.

Biological Significance

In biochemistry, endergonic reactions are crucial for metabolic pathways that require energy input. For example, the synthesis of ATP from ADP and inorganic phosphate is an endergonic process. Cells couple endergonic reactions with exergonic reactions to drive essential biological processes. This coupling often involves the hydrolysis of ATP, which releases energy that can be used to power endergonic reactions.

Examples

• Photosynthesis: The process by which plants, algae, and some bacteria convert light energy into chemical energy stored in glucose is endergonic. The overall reaction requires energy input from sunlight.
• Protein Synthesis: The formation of peptide bonds between amino acids to form proteins is an endergonic process that requires energy input, often provided by the hydrolysis of ATP.

Related Concepts

• Activation energy
• Catalysis
• Endothermic process
• Exergonic reaction
• Metabolism

Related Pages

• Chemical thermodynamics
• Bioenergetics
• Enzyme
• Cellular respiration