Biochem Ch 6 pt 1: Enzyme Thermodynamics

Enzymes

• increase rate of reaction

• decrease activation energy (E_a)

• stabilize transition state

• does not change ∆G of rxn (have no effect on equilibrium positions)

• must return to original form after rxn is complete

Activation energy

Amount of energy needed to go from substrate to transition state

∆G of spontaneous reaction?

∆G < 0

How specifically do enzymes lower activation energy?

Active site of enzyme binding to + forming strongest bond to transition state

Bond between enzyme and transition state

weak, noncovalent bonds

change in binding energy

∆G_B, overall exergonic comparing Ts of catalyzed vs uncatalyzed reaction

Where does the energy come from to overcome E_a from ES to TsE?

• break bonds between substrate and aqueous solution

• break bonds between enzyme and aqueous solution

• increase entropy in solution (hydrophobic residues) —> getting rid of water cages

• break bonds between enzyme and substrate

What is the effect of binding energy ∆G_B, how does binding to an enzyme lower activation energy

1. Specificity- distorts substrate to transition state, aligns catalytic functional groups of enzyme and substrate

2. Reduces entropy/free movement of substrates

3. Helps remove solvation shell of H-bonded water around substrates- removes steric hindrance caused by water

4. Speeds up reactions

binds substrate, often a small cleft within the larger context of polypeptide folds

active site of enzyme

How do enzymes work?

1. Induced fit and strain

2. General acid-base catalysis

3. Covalent catalysis

4. Metal Ion catalysis