Chapter 6

Question 1

What are the two properties of enzymes that make them useful catalysts?

Answer 1

rate enhancement and substrate specificity

Question 2

What are the general characteristics of enzyme active sites?

Answer 2

• 3d cleft…makes up small volume of enzyme
• they have unique microenvironments
• binds to substrate with multiple weak interactions
• specificity of active site depends on 3d structure

Question 3

What does an apoenzyme require to become a holoenzyme?

Answer 3

a cofactor

Question 4

What are the two main types of cofactors?

Answer 4

coenzymes and metals

Question 5

Why are vitamins necessary for good health?

Answer 5

vitamins are converted into coenzymes required for biochem reactions

Question 6

What is the fundamental mechanism by which enzymes enhance the rate of chemical reaction?

Answer 6

enzymes facilitate the formation of the transition state

Question 7

What is the structural basis for enzyme specificity?

Answer 7

3d structure of proteins allow construction of active site that will recognize specific substrates

Question 8

What is meant by binding energy?

Answer 8

free energy released when two molecules bind together, such as when enzyme and substrate interact

Question 9

What is the role of binding energy in enzyme catalysis?

Answer 9

maximized when enzyme interacts with substrate causing formation of transition state and enhances rate of reaction

Question 10

What would be the result of an enzyme having a greater binding energy for the substrate than for the transition state?

Answer 10

no catalytic activity if enzyme-substrate complex is more stable than enzyme transition state complex the transition state wouldnt form and catalysis wouldnt take place

Question 11

What is an enzyme?

Answer 11

protein catalyst

Question 12

What is a substrate?

Answer 12

reactant in enzyme catalyzed reaction

Question 13

What is a cofactor?

Answer 13

coenzyme/metal

Question 14

What is an apoenzyme?

Answer 14

enzyme minus cofactor

Question 15

What is a holoenzyme?

Answer 15

enzyme plus cofactor

Question 16

What is delta G degrees’

Answer 16

function of Keq’

Question 17

What is the transition state

Answer 17

least stable reaction intermediate

Question 18

What is the active site?

Answer 18

site on enzyme where catalysis takes place

Question 19

What is induced fit?

Answer 19

change in enzyme structure

Question 20

Why does the activation energy of a reaction not appear in the final delta G of the reaction?

Answer 20

the energy required to reach transition state proceeds to product

Question 21

Proteins are thermodynamically unstable. The delta G of the hydrolysis of proteins is quite negative, yet proteins can be quite stable. Explain this paradox. What does it tell you about protein synthesis?

Answer 21

protein hydrolysis has large activation energy protein synthesis requires energy to proceed

Question 22

Suggest why the enzyme lysozyme, which degrades cell walls of some bacteria, is present in tears.

Answer 22

lysozyme helps protect the fluid that surrounds eyes from bacterial infection

Question 23

Transition state analogs, which can be used as enzyme inhibitors and to generate catalytic antibodies, are often difficult to synthesize. Suggest a reason.

Answer 23

transition states are very unstable consequently molecules that resemble transition states are likely to be unstable and hence making it difficult to synthesize