5. Enzymes Flashcards
How do enzymes lower the activation energy?
Provide alternative reaction pathway by means of their active site
- Geometric complimentarity: Active site forces the substrate to bind in a configuration that resembles the transition state (ES complex)
- Electronic complimentarity: Amino acid side chains can donate/accept protons, stable covalent ES complex can be formed
What do lyases do?
Cleavage of C-C, C-S and C-N bonds
What do ligases do?
Catalyse bond formation
What is the difference between coenzymes and cofactors?
Coenzymes bind loosely to the enzyme and are required for function (organic molecules)
Cofactors increase the rate of reaction or are required for enzyme function (metal ions)
What is an apoenzyme?
Enzyme without cofactor
Inactive
What is a holoenzyme?
Enzyme with cofactor
Active
Name 3 factors affecting enzyme rate
Temperature
pH
Substrate concentration
What does a small Km value mean?
Enzyme has high affinity for its substrate
What is hexokinase?
Enzyme that phosphorylates hexose sugars
Low Km for glucose but high Km for fructose
What is an inhibitor?
Any substance that can reduce the velocity of an enzyme-catalysed reaction
What is a reversible inhibitor?
Binds to enzyme with non-covalent bonds
Dilution= dissociation and recovery of activity
What is an irreversible inhibitor?
Covalent bonds
Cannot regain activity
Aspirin
What is competitive inhibition?
Inhibitor binds to same site as substrate
Effect can be reversed by increasing substrate conc and can reach same Vmax
Increases Km
What is non-competitive inhibition?
Inhibitor and substrate bind to different sites
Decreased Vmax
Same Km
How can enzymes be regulated?
Phosphorylation and dephosphorylation
Making more or less of the enzyme
Allosteric regulation
