Enzymes

Question 1

Most enzymes are…

Answer 1

Globular proteins

Question 2

Examples of enzyme cofactors

Answer 2

Inorganic (Mg+, Zn+), organic (called coenzymes), prosthetic groups, apoenzymes.

Question 3

Types of coenzymes

Answer 3

Coenzyme A and NAD+.

Question 4

Coenzyme bound to enzyme protein =

Answer 4

Prosthetic group.

Question 5

Apoenzyme

Answer 5

Without coenzyme

Question 6

Holoenzyme

Answer 6

With coenzyme.

Question 7

How does an apoenzyme become active

Answer 7

By binding of coenzyme or cofactor to enzyme. Holoenzyme is formed when it binds to the active site.

Question 8

Oxidoreductases

Answer 8

Catalyze the transfer of electrions.

Question 9

Transferases

Answer 9

Catalyze group transfer reactions.

Question 10

Hydrolases

Answer 10

Catalyze hydrolysis reactions.

Question 11

Lyases

Answer 11

Catalyse cleavage of C-C, C-O, and C-N or other bonds by elimination. Leave behind double bonds or rings.

Question 12

Isomerases

Answer 12

Catalyze the transfer of groups within molecules to yield isomeric forms.

Question 13

Ligases

Answer 13

Catalyze the formation of C-C, C-S, C-O and C-N bonds by condensation reaction coupled to cleavage of ATP or similar cofactor.

Question 14

Enzymes do not…

Answer 14

Affect equilibrium, cannot change free energy.

Question 15

Enzymes do affect…

Answer 15

Rates of reaction, decrease activation energy.

Question 16

How do enzymes lower activation energy?

Answer 16

They organize reactive groups into close proximity and proper orientation (into a fairly rigid ES complex) by using enzyme substrate binding energy.

Question 17

Enzyme active sites are complimentary too…

Answer 17

The transition state of the reaction.

Question 18

Enzyme substrate binding results in…

Answer 18

Reduction of entropy, hindering the reaction.

Question 19

Acid-base catalysis

Answer 19

Give and take protons

Question 20

Covalent catlysis

Answer 20

Change reaction paths. Requires a nucleophile on the enzyme

Question 21

Metal ion catalysis

Answer 21

Use redox cofactors, pKa shifters. Stabilizes negative charges.

Question 22

In steady state conditions…

Answer 22

ES formed = ES consumed

Question 23

ES association and dissociation depend on…

Answer 23

Constants (K) which reflect E and E properties.

Question 24

Reaction rate is proportional to…

Answer 24

ES complex.

Question 25

Kcat

Answer 25

Turnover rate, number of S molecules converted to P per time. Unit is 1/s .

Question 26

Kcat and Km reflect the…

Answer 26

Cellular environment.

Question 27

Enzyme efficieny

Answer 27

The specificity constant, Kcat/Km.

Question 28

Enzyme efficient is limited by…

Answer 28

Specificity.

Question 29

Kinetic mechanism

Answer 29

The order of binding of substrates and release products

Question 30

Competitive inhibition

Answer 30

Competes with substrate for binding, binds to active site, does not affect catalysis. No change in Vmax, apparent increase in Km.

Question 31

Uncompetitive inhibition

Answer 31

Only binds to ES complex, does not affect substrate binding, inhibits catalytic function. Decrease in Vmax, apparent decrease in Km.

Question 32

Mixed inhibition

Answer 32

Binds to enzyme with or without subsrate, binds to regulatory site, inhibits both substrate binding and catalysis. Decrease in Vmax, apparent change in Km.

Question 33

Noncompetitive inhibition

Answer 33

Type of mixed inhibitors where this is no change in Km.

Question 34

Irreversible inhibitors react with…

Answer 34

The enzyme. One molecule can permanently shut off one enzyme molecule.

Question 35

Noncovalent modification: allosteric regulators

Answer 35

Can be positive (improve catalysis) or negative (reduce catalysis).