Enzymes

Question 1

Enzymes

Answer 1

Biological catalysts that do not impact the thermodynamics of a biological rxn but increase the rate at which it occurs

• Lowers the activation energy
• Does not change free energy (G) or enthalpy (H)
• Does not alter equilibrium
• Changes rate of rxn (kinetics)

Question 2

Lock and Key Model

Answer 2

Enzyme active site (lock) is already in the appropriate conformation for the substrate (key) to bind

Question 3

Induced Fit Model

Answer 3

Shape of the active site becomes truly complementary only after the substrate begins binding. These enzymes return to their original shape after the substrate leaves

Question 4

Cofactors

Answer 4

Inorganic molecules and metal ions

• Small so that they can bind to the active site of an enzyme to aid in conformation change. Participate in catalysis by carrying charge through the ionization, polarization or depolarization

Question 5

CoEnzymes

Answer 5

Organic molecules

• Small so that they can bind to the active site of an enzyme to aid in conformation change. Participate in catalysis by carrying charge through the ionization, polarization or depolarization

Question 6

Saturation

Answer 6

All enzyme active sites are occupied by the substrate

As [substrate] increases, the reaction rate also increases until Vmax is reached

Question 7

Vmax

Answer 7

Maximum velocity of reaction; only increased by increasing the [Enzyme]

Question 8

Michaelis-Menten

Answer 8

E+S ES —-> E+P

Vmax [S]
________ = V
Km + [S]

Question 9

Km

Answer 9

Measure of the affinity of an enzyme for its substrate

Increased Km means decreased affinity because
Km = 1/2 Vmax = [S]

Question 10

Competitive Inhibition

Answer 10

Binds to E at the Active Site
Increases Km
Vmax remains unchanged

**Overcome by adding excess Substrate

Question 11

NonCompetitive Inhibition

Answer 11

Binds to E and ES at an Allosteric Site
Km Remains unchanged
Vmax Decreases

Question 12

Uncompetitive Inhibition

Answer 12

Binds to ES at an Allosteric Site
Km decreases
Vmax Decreases

Question 13

Mixed Inhibition

Answer 13

Binds to E and ES at Allosteric Site
Km can increase or decrease
Vmax Decreases

Question 14

Feedback Regulation

Answer 14

Regulation by products created further down in the pathway

Question 15

Feed Forward Regulation

Answer 15

Intermediates preceding the enzyme are the regulators

Question 16

Negative Feedback Regulation

Answer 16

Product binds to the active site of an enzyme earlier in the pathway inhibiting them or making them unavailable

Question 17

Allosteric Enzymes

Answer 17

Contain multiple binding sites

Question 18

Covalently Modified Enzymes

Answer 18

Transient - allosteric activation / inhibition

Covalent - glycoslation / phosphorylation

Question 19

Zymogens

Answer 19

Inactive Enzyme; contain a regulatory domain which must be removed or altered to expose the active site

Question 20

Ligases

Answer 20

Responsible for joining two large biomolecules (often of the same type)

Question 21

Isomerases

Answer 21

Catalyze the interconversion of isomers, including both constitutional and stereoisomers

Question 22

Lyases

Answer 22

Catalyze cleavage without the addition of water and without the transfer of electrons

*Reverse rxn = synthesis

Question 23

Hydrolases

Answer 23

Catalyze cleavage with the addition of water

Question 24

Oxidoreductases

Answer 24

Catalyze oxidation - reduction reactions that involve the transfer of electrons

Question 25

Transferases

Answer 25

Move a functional group from one molecule to another molecule