L20: Catalytic Power

Question 1

High energy transition state

Answer 1

Bonds are partially broken (enthalpy change positive), reactants become more ordered (entropy change negative)

Free energy of activation = enthalpy change - temp x entropy change -> free energy of activation always positive

Question 2

Catalyst

Answer 2

Lower free energy of transition state

Stabilise transition state

Reduce free energy of activation -> increase rate constant for reaction

Question 3

Transition states in enzyme catalysed reactions

Answer 3

1. Binding of substrate to enzyme active site
2. For the reaction itself
3. For dissociation of product from enzyme active site

Question 4

Intermediates

Answer 4

Enzyme-catalysed reactions proceeds via intermediates that don’t occur in uncatalysed reaction

Advantage of having intermediate: reaction split into 2 separate steps -> each have own transition state. Have lower free energies of activation -> enhancing rate of reaction

Question 5

Arrhenius plots

Answer 5

Describe temp dependency of rate constant for reaction

In enzyme catalysed reactions: rate of reaction is measured at high (saturating) [subs] at different temps -> rate of reaction is function of rate constant of rate limiting step in reaction, kcat

Gives activation energy, Ea

R: gas constant

Question 6

Catalytic power

Answer 6

Ratio of rate constant of catalysed reaction to that of uncatalysed reaction

Question 7

Calculated activation parameters

Answer 7

Give info about enthalpy and entropy changes required to get transition stage of slowest step of reaction i.e. one with highest energy barrier that governs rate if overall reaction