Basic Concepts of Enzyme Action

Question 1

What do enzymes do?

Answer 1

Accelerate the rate of rxns, highly specific in both the rxns they catalyze and choice of reactants (substrate)

Question 2

What are proteolytic enzymes?

Answer 2

Catalyze proteolysis, which is hydrolysis of a peptide bond (breakage of bond with H2O), differ greatly in degrees of substrate specificity

Question 3

What are the six major classes of enzymes?

Answer 3

1. Oxidoreductases
2. Transferases
3. Hydrolases
4. Lyases
5. Isomerases
6. Ligases

Question 4

Oxidoreductases

Answer 4

Catalyze redox rxns (transfer e- between molecules)

Question 5

Transferases

Answer 5

Transfer functional groups between molecules

Question 6

Hydrolases

Answer 6

Cleaves molecules by addition of H2O

Question 7

Lyases

Answer 7

Adds atoms or functional groups to a double bond or removes them to form a double bond

Question 8

Isomerases

Answer 8

Move functional groups within a molecule

Question 9

Ligases

Answer 9

Join 2 molecules in rxn powered by ATP hydrolysis

Question 10

Enzymes often cannot meet the chemical needs required for catalysis to take place, so they depend on

Answer 10

the presence of cofactors (small molecules)

• Enzyme without cofactor = apoenzyme
• Enzyme with cofactor = holoenzyme

Question 11

Cofactors are divided into 2 groups:

Answer 11

1. Coenzymes

2. Metals

Question 12

Coenzymes

Answer 12

Small organic molecules derived from vitamins, similar to cosubstrates bc they bind to the enzyme and are released from it, used by variety of enzymes

Question 13

Metals

Answer 13

Bound at the active site and participate in the rxn

Question 14

Free Energy Change

Answer 14

For spon, deltaG = (-)
At equil, deltaG = 0
deltaG is independent of pathwaymechanism of transformation
deltaG tells NOTHING about rate of rxn

Question 15

For a rxn to be energetically favourable (spon), deltaG must be

Answer 15

negative
Spon rxns are NOT instantaneous
Enzymes make a spon rxn kinetically favourable

Question 16

How do enzymes accelerate rxns?

Answer 16

By decreasing the activation energy to overcome the activation energy barrier
Enzymes lower the activation energy by stabilizing the transition state

Question 17

What are the features of enzyme active sites?

Answer 17

1. Residues forming the active site come from different positions in the primary sequence
2. Small volume of total protein
3. Unique microenvironment (polar residues on inside when normally outside)
4. Forms many weak interactions with substrates
5. Specificity of substrate binding depends on the precise arrangement of atoms in the active site

Question 18

What is binding energy?

Answer 18

The free energy that is released when many weak interactions form between the enzyme and substrate and transition state
- Only the correct substrate can maximize the amount of binding energy = specificity

Question 19

When does maximal binding energy occur?

Answer 19

During the formation of the transition state