enzyme energetics + thermodynamics and equilibrium

what is the thermodynamics of a reaction?

• predicts if a reaction is possible

• focus on energy difference between substrate and product

• looking at equilibrium positions and spontanaeity

what is thermodynamics determined by?

ΔG (change in Gibbs free energy)

how is ΔG measured?

energy difference between substrate and product

what is the kinetics of a reaction?

• rate of reaction

• focus on factors that affect reaction rates

• focus on different reaction mechanisms

what determines reaction kinetics?

E_A (activation energy)

the higher the E_A, the slower the reaction

what is activation energy?

the minimum amount of energy required to initiate a chemical reaction

how is activation energy measured?

energy differnce between transition state and substrate

what is gibb’s free energy change?

change in free energy between reactant and product

what does it mean if ΔG is negative?

reaction favours product formation (forwards reaction)

product is more stable than substrate

favourable reaction as system’s free energy is decreased

can take place spontaneously

what does it mean if ΔG is positive?

reaction favours reactant/substrate formation (reverse reaction)

substrate is more stable than product

unfavourable reaction as system’s free energy is increased

cannot take place spontaneously

what does it mean when ΔG = 0?

the reaction is at equilibrium (equal rate of formation and dissociation)

what factors is ΔG dependent on?

concentration (of reactants/products), temperature…

what is a transition state?

• point where bonds are in the process of breaking/forming

• peak of energy barrier

reaction coordinate diagram for an exothermic reaction (-ΔG)

reaction coordinate diagram for an endothermic reaction?

what is the equilbrium constant, K_eq?

ratio of product concentration to reactant concentration at equilibrium

calculated at a specific temperature

what is the equation for K_eq?

what is teh equation for ΔG°? (standard gibb’s free energy change)

what does it mean when K_eq > 1?

• ΔG is negative

• concentration of products > concentration of reactants

what does it mean when K_eq < 1?

• ΔG is positive

• concentration of reactants > concentration of products

what does it mean when K_eq = 0?

• ΔG = 0

• concentration of products = concentration of reactants