Enzyme Regulation

Question 1

What is another name for negative feedback?

Answer 1

Feedback inhibition

Question 2

What occurs during negative feedback (or feedback inhibition)?

Answer 2

An end product “feedsback” and inhibits the beginning of a pathway.

(maintains homeostasis by preventing over accumulation of product)

Question 3

What occurs during positive feedback?

Answer 3

An end product returns to the beginning of a pathway and activates it.

(increases the rate of product production)

Question 4

What are the f__our types of reversible inhibitors?

Answer 4

1. competitive
2. noncompetitive
3. mixed
4. uncompetitive

Question 5

What is the function of a noncompetitive inhibitor?

Answer 5

Binds to an allosteric site of an enzyme OR an E-S complex with the same affinity.

Question 6

What is the function of a competitive inhibitor?

Answer 6

Competes with substrate for the active site of an enzyme.

The substrate and competitive inhibitor are structurally similar, that is why they both compete for the active site.

Question 7

What effect does a competitive inhibitor have on K_m and V_max?

Answer 7

• increases K_m
• NO change in V_max

Question 8

What effect does a noncompetitive inhibitor have on K_m and V_max?

Answer 8

• NO change K_m
• decreases V_max

Question 9

[Mnemonic]

Kompetitive inhibitor: K_m increases

Nonkompetitive inhibitor: NO change in K_m

(how to remember the functions of a competitive and noncompetitive inhibitor)

Answer 9

1. Kompetitive inhibitor
   
   1. K_m increases
   2. NO change in V_max
2. Nonkompetitive inhibitor
   
   1. NO change in K_m
   2. V_max decreases

Question 10

What is the function of an uncompetitive inhibitor?

Answer 10

When an E-S complex is formed, the active site undergoes a conformational change and creates an allosteric site. An uncompetitive inhibitor binds to that allosteric site and an E-S-I complex is formed.

Question 11

What is the function of a mixed inhibitor?

Answer 11

Binds to either an enzyme OR an E-S complex with different affinities.

Hence why they are called “mixed”.

Question 12

Which reversible inhibitor is the ONLY kind that binds to the active site of an enzyme?

Answer 12

Competitive inhibitor

Question 13

How are the effects of competitive inhibition overcome?

Answer 13

By increasing substrate concentration.

If more molecules of substrate are available than molecules of inhibitor, then the enzyme will be more likely to bind to the substrate than the inhibitor.

Question 14

What is k_cat/K_m?

Answer 14

A measure of enzyme efficiency.

• High k_cat/ low k_m = high enzyme efficiency
• Low k_cat/high k_m = low enzyme efficiency

(at saturating conditions)

Question 15

What is the equation for solving K_cat?

Answer 15