Overview of Enzymes

Question 1

What is the main function of enzymes?

Answer 1

Lower the activation energy (E_A) for a reaction.

Question 2

Enzymes are biological catalysts. What is the significance of this?

Answer 2

Enzymes increase reaction rates which increases the amount of product formed per unit of time.

Question 3

What are substrates?

Answer 3

Reactants acted upon by enzymes.

Question 4

What is the active site of an enzyme?

Answer 4

Location where the substrate binds.

Question 5

What is enzyme specificity?

Answer 5

The active site of an enzyme only binds a specific substrate.

Question 6

What is an enzyme-substrate complex?

Answer 6

A complex formed when an enzyme and substrate bind tightly together.

Question 7

What is activation energy?

Answer 7

The minimum amount of energy needed to start a chemical reaction.

Question 8

Why is it so important for enzymes to lower activation energy (E_A)?

Answer 8

Because it decreases the barrier for starting a reaction.

(If the energy barrier is lower, then the enzyme can catalyze the reaction much faster, thus increasing reaction rate.)

Question 9

What does the induced fit model state?

Answer 9

A substrate binds to an enzyme and induces a conformational change in its active site, so that they are a complementary fit.

Question 10

What are cofactors?

Answer 10

Inorganic molecules (or metal ions)

Example: minerals

Question 11

What are coenzymes?

Answer 11

Organic molecules

Example: vitamins or vitamin derivatives

Question 12

What is the main function of both cofactors and coenzymes?

Answer 12

Activate enzymes by inducing conformational changes.

Question 13

What is a holoenzyme? Apoenzyme?

Answer 13

holoenzyme: An enzyme WITH its cofactor

apoenzyme: An enzyme WITHOUT its cofactor

(completely nonfunctional)

Question 14

What is a zymogen?

Answer 14

An inactive form of an enzyme.

Question 15

What is V_max?

Answer 15

How fast an enzyme can catalyze a reaction.

(the rate of reaction when the enzyme is saturated with substrate)

Question 16

What is K_m (or Michaelis constant)?

Answer 16

Substrate concentration at which the reaction rate is equal to 1/₂Vmax.

(K_m = 1/₂V_max)

Question 17

When does saturation kinetics occur?

Answer 17

When V_max has been reached.

Adding more substrate will NOT increase reaction rate, once V_max has been reached.

Question 18

A low K_m, has what kind of substrate affinity?

Answer 18

low K_m = high substrate affinity

Question 19

A high K_m, has what kind of substrate affinity?

Answer 19

high K_m = low substrate affinity

Question 20

What is K_m inversely proportional to?

Answer 20

Enzyme-substrate affinity

Question 21

What are the three main factors that affect the rates of enzymes?

Answer 21

1. temperature
2. pH
3. salinity (increasing levels of salt can disrupt hydrogen and ionic bonds)

Question 22

What is the optimal temperature for enzymes in the human body?

Answer 22

37° C

[37°C = 98.6°F = 310 K]

Question 23

When does an enzyme or protein exhibit cooperativity?

Answer 23

When there are multiple binding sites or subunits.

Cooperativity results in a sigmoidal shape curve (s-shape).

Question 24

What is the Hill coefficient (n_H)?

Answer 24

A measure of the cooperativity of substrate binding to an enzyme.

Question 25

For the Hill coefficient (n_H), what does it mean if:

• n_H = 0
• n_H > 1
• n_H < 1

Answer 25

• n_H = 0 NO cooperativity
  
  • The enzyme follows normal M-M kinetics​.
• n_H > 1 positive cooperativity
  
  • ​i.e. hemoglobin binding with oxygen
• n_H < 1 negative cooperativity
  
  • If it’s essentially one ( such as 1.1, or 1.2) it is still considered negative cooperativity.

Question 26

What is an endergonic (or nonspontaneous) reaction?

Answer 26

A reaction that requires energy input.

ΔG > 0

Question 27

What is an exergonic (or spontaneous) reaction?

Answer 27

A reaction that releases energy.

ΔG < 0

Question 28

What occurs when a homogenous catalyst is not separated from products at the end of a reaction?

Answer 28

The products will be contaminated.

Question 29

How will the rate of a catalyzed reaction be affected if the solid catalyst is finely ground before being added to the reaction mixture?

Answer 29

The rate will be faster because a greater surface area of catalyst will be exposed.