How enzymes work

Question 1

What do enzymes do?

Answer 1

Speed up reactions, but they do not change the equilibrium of the reactions (i.e. they change the kinetics of a reaction but mot its equilibrium)

Question 2

How does an enzyme speed up a reaction? and how?

Answer 2

By reducing the activation energy of the reaction

• Enzymes form a tight complex with the transition state of the substrate, thereby facilitating its conversion into the product

Question 3

Use digestion of carbohydrates as an example

Answer 3

• transition state is a carbohydrate in an altered conformation
• In addition, the carbon atom C1 is attacked by an aspartate residue acting as a general base and a glutamate residue acting as a general acid (donating a proton) - both being located close to a glycosidic bond
• A covalent intermediate is formed as part of the catalytic process

Question 4

What are the general principles of enzymatic catalysis?

Answer 4

• The enzymes come out at the end of the reaction in the state it entered
• Enzymes bind tightly to the transition state of the substrate. This can result in distortion of the substrate allowing reactions to occur more easily
• Enzymes bring reactant into close proximity and optimal orientation
• Enzymes speed up reactions but do not change the equilibrium
• Active residues are found in the catalytic center participating in the reaction

Question 5

Enzymatic catalysis makes use of different active residues, these can be categorised as …

Answer 5

• General acid and general base catalysis (i.e. glycosidic bond hydrolysis)
• Covalent catalysis (i.e. glycosidic bond hydrolysis)
• Metal ion catalysis