- Energy
- First Law of Thermodynamics
- Enthalpy (H): total bond energy in a molecule
- Second Law of Thermodynamics
- Entropy (S): system moves to greater disorder
- Free Energy (G): available energy
- Concept: Using either enthalpy or entropy alone, it is not possible to predict in which direction a reaction is spontaneous. However, free energy (G=H-TS) can be used to determine the spontaneous direction of a reaction.
- Equilibrium (constant):Keq = concentration of products divided by reactants when a reaction ceases to change from products to reactants or the reverse.
- exothermic vs endothermic
- exergonic vs endergonic
- spontaneous reaction: a reaction that is exergonic under cellular conditions (free energy change is negative) is spontaneous.
- Concept: For biological processes to be spontaneous, each step of the process (pathway) must be spontaneous under cellular conditions.
- To turn a non-spontaneous reaction into a spontaneous reaction, two methods are used in biological systems:
- coupled reaction: use the energy provided by an exergonic (spontaneous) reaction to drive an endergonic (non-spontaneous) reaction.
- example: Use the energy from the spontaneous hydrolysis of ATP (7 Kcal/mole) to "drive" a non-spontaneous reaction requiring less than 7 Kcal/mole.
- Concept: Free energy is additive
- Change the cellular concentrations of reactants and products: apply the Law of Mass Action (increase reactants and decrease products)
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