Lecture I - Enzymes II - Catalysis

Question 1

What are two things enzymes do? What are two things enzymes don’t do?

Answer 1

Do:
Lower the activation Energy
Stabilize the transition state

Don’t:
Change the DeltaG of the reaction
Irreversibly change shape.

Question 2

What is a catalyst? (2)

Answer 2

Increases the rate of a reaction

Does not undergo any permanent chemical change as a result.

Question 3

What are two biochemical strategies to drive an unfavorable reaction? (DeltaG +)

Answer 3

1. Maintain Q

Question 4

What is a transition state?

Answer 4

A high energy, unstable form of the reactant(s) that is ready to form product(s).

Question 5

What is Activation Energy?

Answer 5

An energy barrier that must be overcome for the reaction to proceed.

Question 6

What are the two listed ways to speed up a reaction?

Answer 6

1. Raise the Temperature

2. Stabilize the transition state (short for use an enzyme!)

Question 7

What is the induced fit model?

Answer 7

When the enzyme changes shape after a substrate binds, so that the substrate is forced into the transition state.

Question 8

Catalysis is achieved through? (4)

Answer 8

Substrate orientation

Straining substrate bonds

Creating a favorable microenvironment

Covalent and/or noncovalent interactions between enzyme and substrate.

Question 9

What is covalent catalysis?

Answer 9

When the Enzyme covalently binds the transition state. (electrons transfer)

Question 10

What is Acid-Base catalysis?

Answer 10

Partial proton transfer to the substrate.

Question 11

What is approximation?

Answer 11

When proper spatial orientation and close contact of the reactant molecules occur. Because they are held in close proximity to one another, they are more likely to react.

AKA entropy reduction

Question 12

What is electrostatic catalysis?

Answer 12

Stabilization of unfavorable charges on the transition state by polarizable side chains in the enzyme and/or metal ions.

Question 13

What kind of active site does chymotrypsin have?

Answer 13

Catalytic Triad

• Serine (S195) (nucleophile)
• Histidine (H57) (base)
• Aspartic Acid (D102) (proton donor)

Question 14

What is an oxyanion hole? What is in the oxyanion hole of chymotrypsin?

Answer 14

An oxyanion hole is a pocket in the active site of an enzyme that helps stabilize the tetrahedral intermediate negative charge.

• Serine (S195)
• Glycine (G193)

Question 15

What does the specificity (s1) pocket of chymotrypsin do?

Answer 15

Determines placement of cut

Question 16

What does the active site of Carbonic Anhydrase contain?

Answer 16

Zn++ ion coordinated to three histidine molecules and a water molecule

Question 17

What is the purpose of the water molecule in the active site of Carbonic Anhydrase?

Answer 17

It facilitates the transition state.

• Becomes Deprotonated
• Catalytic strategy of approximation

Question 18

What is the function of an Entry Channel? What is the entry channel functional group of Carbonic Anhydrase?

Answer 18

Entry channel determines the size of the substrate

CO2 - small and weakly polar