Chapter 2: Enzymes

Question 1

What does endothermic mean?

Answer 1

A reaction that requires energy input

ΔH is positive

Question 2

What does exothermic mean?

Answer 2

A reaction in which energy is given off.

ΔH is negative

Question 3

How do enzymes affect the equilibrium of a reaction?

Answer 3

They do not affect the equilibrium.

They DO affect the rate of reaction

Question 4

How do enzymes affect the rate of reaction?

Answer 4

The increase the rate of reaction by lowering the activation energy.

They make it easier for the substrate to reach the transition state.

Question 5

What is a substrate?

Answer 5

The molecule upon which an enzyme acts

Question 6

What is the enzyme active site?

Answer 6

The location within the enzyme where the substrate is held during the chemical reaction

Question 7

What is the lock and key theory?

Answer 7

The enzyme’s active site (lock) is already in the appropriate confirmation for the substrate (key) to bind

No changes in tertiary or quarternary structure occur

Question 8

What is the induced fit theory?

Answer 8

A substrate induces an appropriate conformational shift in the enzyme leading to the exposure of the active site. Following the reaction, the enzyme will return to its original shape

Question 9

What is an apoenzyme?

Answer 9

Enzymes without their cofactors

Question 10

What is a holoenzyme?

Answer 10

Enzymes with their cofactors

Question 11

What is the major factor in reaction rate?

Answer 11

The concentration of the substrate [S] and enzyme [E] greatly affects how quickly a reaction will occur

Question 12

Explain what enzyme saturation is

Answer 12

When substrate concentration is raised past a certain point, an enzyme has no available active sites for the excess substrate.

The enzyme is working at maximum velocity

The rate of reaction past the saturation point is independent of [S]

Question 13

What is the [S] when the reaction rate equals 1/2 Vmax?

Answer 13

[S] = Km, the Michaelis Menten constant

Question 14

What is the optimal pH of human blood?

Answer 14

7.4

Question 15

Is a blood pH = 7.3 considerd acidosis or alkylosis?

Answer 15

Acidosis because the pH is lower than the normal blood level of 7.4

Question 16

What is an allosteric enzyme?

Answer 16

An enzyme with multiple binding sites. One site is the active site, and another is a regulatory site that can affect the availability of the active site

Sigmoidal binding curve = Allosteric enzyme

Question 17

What is competitive inhibition?

Answer 17

When an inhibitor can occupy the active site, thus preventing substrate binding. The substrate and inhibitor compete for access to the binding site.

This can be overcome by increasing [S]

Question 18

What is noncompetitive inhibition?

Answer 18

When an inhibitor binds to an allosteric site instead of the active site. The two molecules do not compete, so increasing [S] will not overcome the inhibition

Question 19

What is irriversible inhibition?

Answer 19

When the active site of an enzyme is made permanently unavailable or the enzyme is permanently altered.

Question 20

What is a zymogen?

Answer 20

Inactive forms of enzymes that contain a catalytic and a regulatory domain. The regulatory domain is removed or altered in order to expose the active site.