Lecture 12 - Enzymatic catalysis

Question 1

Enzymes are good catalysts due to their

Answer 1

specificity of substrate binding and optimal arrangement of catalytic groups

Question 2

Enzymatic catalytic mechanisms are divided into what six classes?

Answer 2

1. Acid-base catalysis
2. Covalent catalysis
3. Metal ion catalysis
4. Electrostatic catalysis
5. Proximity and orientation effects
6. Preferential binding of the transition state complex

Question 3

General acid catalysis involves

Answer 3

partial proton transfer from a Brønsted acid

Question 4

General base catalysis involves

Answer 4

partial proton abstraction from a Brønsted base

Question 5

RNase A is a digestive enzyme that functions to

Answer 5

hydrolyze RNA to individual nucleotides

Question 6

RNase A contains what two important residues?

Answer 6

His 12 and His 119

Question 7

In RNase A, what acts as the general base?

Answer 7

His 12

Question 8

In RNase A, what acts as the general acid?

Answer 8

His 119

Question 9

In covalent catalysis, reaction rates are accelerated through

Answer 9

the transient formation of a catalyst-substrate covalent bond

Question 10

In covalent catalysis, the covalent bond is usually formed by the reaction of a nucleophilic group on the ______ with an electrophilic group on the ______

Answer 10

catalyst; substrate

Question 11

A good covalent catalyst must combine the properties of

Answer 11

high nucleophilicity and the ability to form a good leaving group

Question 12

Groups with ________ make good covalent catalysts

Answer 12

highly mobile electrons

Question 13

Which amino acids make good covalent catalysts?

Answer 13

• Histidine
• Cysteine
• Aspartate
• Serine

Question 14

Serine proteases are a class of

Answer 14

proteolytic enzymes in which a serine hydroxyl plays an essential role in catalysis

Question 15

In chymotrypsin, the oxygen of the serine side chain

Answer 15

attacks the carbonyl group of the peptide

Question 16

Two classes of enzymes that contain metal ions

Answer 16

1. Metalloenzymes
2. Metal-activated enzymes

Question 17

Metalloenzymes include

Answer 17

tightly bound ions and transition metal ions

Question 18

Metal-activated enzymes include

Answer 18

loosely bound ions from the solution and alkali and alkaline earth metal ions

Question 19

Metal ions often act to

Answer 19

neutralize negative charges

Question 20

Metal ions act much in the same way as a ______ to neutralize negative charges.

Answer 20

proton

Question 21

A metal ion’s charge makes a bound water molecule more

Answer 21

acidic

Question 22

The Zn+2 ion of carbonic anhydrase lies at the

Answer 22

bottom of an active site cleft

Question 23

The most important function of carbonic anhydrase in animals is to

Answer 23

maintain acid-base balance in blood and other tissues

Question 24

Carbonic anhydrase helps to transport

Answer 24

carbon dioxide out of tissues

Question 25

Zn+2 polarizes a water molecule to form

Answer 25

OH-

Question 26

Another important role of metal ions is

Answer 26

charge shielding

Question 27

DNA polymerases require ______ for activity

Answer 27

metal ions

Question 28

In electrostatic catalysis, an active site often excludes

Answer 28

water

Question 29

Electrostatic interactions are much stronger than in

Answer 29

aqueous solutions

Question 30

In electrostatic catalysis, charge distribution guides polar substrates to the

Answer 30

active site

Question 31

In proximity, the reaction between bound molecules doesn't require

Answer 31

an improbably collision of 2 molecules

Question 32

In orientation effects, reactants are not only close to each other, they're

Answer 32

oriented in optimal position to react

Question 33

When imidazole is attached to the reactant, the reaction is _____ times faster

Answer 33

24

Question 34

In catalysis by preferential transition state binding, the rate is _____ times faster when R is CH3 rather than H

Answer 34

315

Question 35

Transition state analogs are often

Answer 35

enzyme inhibitors