CH 6: Enzymes

Flashcards about Enzymes

What are enzymes?

Protein catalysts that accelerate reaction rates.

What are reactants in enzyme-catalyzed reactions called?

Substrates.

Name two proteolytic enzymes mentioned in the lecture.

Trypsin and thrombin.

What enzyme is required for the reaction of adding water to carbon dioxide in red blood cells?

Carbonic anhydrase.

Name the six major classes of enzymes.

Oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.

What is the function of oxidoreductases?

Catalyze oxidation-reduction reactions.

What is the function of transferases?

Move functional groups between molecules.

What is the function of hydrolases?

Cleave bonds with the addition of water.

What is the function of lyases?

Remove atoms to form double bonds or add atoms to double bonds.

What is the function of isomerases?

Move functional groups within a molecule.

What is the function of ligases?

Join two molecules at the expense of ATP.

What are cofactors?

Small molecules some enzymes require for activity.

Name the two main classes of cofactors.

Coenzymes and metals.

What are cofactors tightly bound to enzymes called?

Prosthetic groups.

What is an enzyme with its cofactor called?

Holoenzyme.

What is an enzyme without its cofactor called?

Apoenzyme.

What is free energy (G)?

A measure of energy capable of doing work.

What does ΔG represent?

The change in free energy when a reaction occurs.

Do enzymes alter the ΔG of a reaction?

No.

What is the ΔG at equilibrium?

Zero.

What is an exergonic reaction?

A reaction that occurs spontaneously with a negative ΔG.

What is an endergonic reaction?

A nonspontaneous reaction with a positive ΔG that requires energy input.

What is the transition state?

A molecular form that is no longer substrate but not yet product.

What is activation energy?

The energy required to form the transition state from the substrate, symbolized by ΔG‡.

How do enzymes facilitate the formation of the transition state?

By lowering the activation energy.