Chapter 2: Enzymes

Question 1

Enzymes act as catalysts to impact which of the following in a reaction: thermodynamics, equilibrium position, and reaction rate

Answer 1

Rate of reaction

Question 2

What are the key features of an enzyme? (7)

Answer 2

1. lower the activation energy
2. increase rate of reaction
3. do not alter equilibrium constant
4. are not changed or consumed in the reaction
5. are pH- and temperature-sensitive, with optimal activity at specific pH ranges and temperatures
6. Do not affect the overall delta G of the reaction
7. Are specific for a particular reaction or class of reactions

Question 3

The molecules upon which an enzyme acts are called:

Answer 3

Substrates

Question 4

What are the six categories of enzymes? (hint: Lil hot)

Answer 4

1. Ligases
2. Isomerases
3. Lyases
4. Hydrolases
5. Oxireductases
6. Transferases

Question 5

How do cofactors and coenzymes differ?

Answer 5

Cofactors are generally metal cations, and coenzymes are small organic molecules that are generally derived from vitamins.

Question 6

Enzymes that require a cofactor but do not have them are called:

Answer 6

Apoenzymes

Question 7

Enzymes that require a cofactor and do contain them are called:

Answer 7

Holoenzymes

Question 8

Enzymes that are secreted in an inactive form with a regulatory domain that must be removed or altered to become active are called:

Answer 8

Zymogens

Question 9

What is the function of oxidoreductases?

Answer 9

Catalyze oxidation-reduction reactions; i.e., the transfer of electrons between two biological molecules.

Question 10

What is the function of transferases?

Answer 10

Catalyze the movement of a functional group from one molecule to another

Question 11

What is the function of kinases?

Answer 11

Catalyze the transfer of a phosphate group to another molecule (generally from ATP to another molecule)

Question 12

What is the function of hydrolyses?

Answer 12

Catalyze the breaking of a compound into two molecules using the addition of water

Question 13

What is the function of lyases?

Answer 13

Catalyze the cleavage of a single molecule into two products without water. In reverse, they act as synthases. Generally act upon smaller molecules.

Question 14

What is the function of isomerases?

Answer 14

Catalyze the rearrangement of bonds within a molecule

Question 15

What is the function of ligases?

Answer 15

Catalyze addition or synthesis reactions, generally between large similar molecules and often requiring ATP.

Question 16

Define Vmax

Answer 16

the maximum velocity of an enzyme, found at saturation

Question 17

Define Km

Answer 17

The substrate concentration at which 1/2 of the enzymes are full

Question 18

What is the michaelis-mentin equation

Answer 18

V= (Vmax[S])/(Km+[S])

Question 19

What is the equation for Vmax of an enzyme?

Answer 19

Vmax = [E]Kcat

Question 20

In a Lineweaver-Burk plot, what value is found at the intercept of the line with the x-axis?

Answer 20

-1/Km

Question 21

What is a Lineweaver-Burk plot?

Answer 21

a double reciprocal graph of the Michaelis-Menten equation

Question 22

In a Lineweaver-Burk plot, what value is found at the intercept of the line with the y-axis?

Answer 22

1/Vmax

Question 23

What is positive cooperative binding?

Answer 23

Substrate binding that increases the affinity for a subsequent substrate

Question 24

What is negative cooperative binding?

Answer 24

Substrate binding that decreases affinity for subsequent substrate

Question 25

What is Hill's coefficient?

Answer 25

A quantifiable numerical value that indicates cooperativity

Question 26

Hill's coefficient > 1 means what?

Answer 26

Positive cooperative binding

Question 27

Hill's coefficient < 1 means what?

Answer 27

Negative cooperative binding

Question 28

Hill's coefficient = 1 means what?

Answer 28

No cooperative binding

Question 29

A maximally efficient enzyme has a (high/low) Kcat and a (high/low) Km

Answer 29

High Kcat and low Km

Question 30

What is the variable for catalytic turnover?

Answer 30

Kcat

Question 31

What is the variable for substrate affinity?

Answer 31

Km

Question 32

How do we find the catalytic efficiency of an enzyme?

Answer 32

Kcat/Km

Question 33

An increase in Km indicates what?

Answer 33

Decrease in affinity

Question 34

What is the ideal pH for most enzymes in the body?

Answer 34

7.4

Question 35

Competitive inhibitor binding site and impact on Km and Vmax

Answer 35

Active site on E Increases Km No impact on Vmax

Question 36

Noncompetitive inhibitor binding site and impact on Km and Vmax

Answer 36

Allosteric site on E or ES No impact on Km Decreases Vmax

Question 37

Mixed inhibitor binding site and impact on Km and Vmax

Answer 37

Allosteric site on E or ES Increases or decreases Km Decreases Vmax

Question 38

Uncompetitive inhibitor binding site and impact on Km and Vmax

Answer 38

Allosteric site on ES Decreases Km Decreases Vmax

Question 39

Define irreversible inhibition

Answer 39

Inhibition that permanently makes an active site unavailable

Question 40

Phosphorylation is an example of what type of enzyme modification?

Answer 40

Covalent modification

Question 41

Define zymogens

Answer 41

Inactive enzymes with a catalytic (active) and a regulatory domain, the latter of which must be removed or altered to expose the active site