Enzymes and enzyme kinetics

Question 1

Oxidoreductases

Answer 1

Catalyze oxidation/reduction rxns

Question 2

Transferases

Answer 2

Catalyze movement of functional groups

Question 3

Hydrolases

Answer 3

Catalyze the breaking of compounds with water

Question 4

Lyases

Answer 4

Catalyze the cleavage of one compound into two

Question 5

Isomerases

Answer 5

Catalyze bond rearrangement within a molecule

Question 6

Ligases

Answer 6

Catalyze addition or synthesis rxns

Question 7

Km

Answer 7

Equals the [S] at 1/2 Vmax
-The Michaelis-Menton constant

Question 8

Kcat

Answer 8

Measures the amount of substrate converted into product

(the amount CATalyzed)

Question 9

Catalytic efficiency ratio and meaning

Answer 9

Kcat/Km

How efficient the enzyme is at converting substrate into product

Question 10

What is enzyme cooperativity and how is it measured?

Answer 10

Cooperativity is a measure of whether or not the affinity for a ligand increases as more active sites are bound (ex: binding to one active site increases the enzymes affinity for the next active site)

Measured by Hills coefficient:
>1 positive cooperativity
=1 no cooperative binding
<1 negative cooperativity

Question 11

Competitive inhibition:
Binding site
Vmax ____
Km ___

Answer 11

Active site
Vmax stays the same (can be outcompeted)
Km increases (affinity for S decreases, but Km is inverse)

Question 12

Non-competitive inhibition:
Binding site
Vmax ____
Km ___

Answer 12

Bind equally well to the E+S and ES complex
Vmax decreases
Km stays the same (think of non-competitive like a special type of mixed inhibitor. Since it can bind either the E+S or ES complex, the change in Km is negligible and looks like there’s no change overall)

Question 13

Mixed inhibition:
Binding site
Vmax ____
Km ___

Answer 13

Allosteric site of either E+S or ES complex
Vmax always decreases
Km increases if binding E+S (because S can’t bind if there’s a conformation change)
Km decreases if binding ES (because the enzyme won’t let go of the S, so it looks like it has a high affinity)

Question 14

Uncompetitive inhibition:
Binding site
Vmax ____
Km ___

Answer 14

Allosteric site of ES only
Vmax decreases
Km decreases (E never releases S, so less product will be formed)

Question 15

Allosteric enzymes

Answer 15

Have allosteric sites that, when bound, affect the affinity of active sites
-can turn active sites on or off by inducing a conformation change

Question 16

Covalently modified enzyme

Answer 16

Modify enzyme by creating new bonds

Ex: glycoslyation, phosphorylation

Question 17

Zymogens control ____

Answer 17

Enzymes that otherwise would be harmful if they were never turned off
-Have a regulatory domain that can be turned on or off to make sure the enzyme doesn’t go out of control