Enzymes (Ch. 6)

Question 1

Cofactor

Answer 1

Chemical component needed by some enzymes. Can be inorganic ion or a complex organic molecule called a Coenzyme.

Question 2

Coenzyme

Answer 2

(Cofactor) Act as transient carriers of specific functional groups.

Question 3

Prosthetic group

Answer 3

A coenzyme or metal ion that is very tightly bound to the enzyme, or even covalently bound.

Question 4

Oxidoreductases

Answer 4

Class of enzymes that catalyzes the transfer of electrons (hydride ions or H atoms).

Question 5

Transferases

Answer 5

Class of enzymes that catalyzes group transfer reactions.

Question 6

Hydrolases

Answer 6

Class of enzymes that catalyzes hydrolysis reactions (transfer of functional groups to water).

Question 7

Lyases

Answer 7

Class of enzymes that

Question 8

Isomerases

Answer 8

Class of enzymes that catalyzes the transfer of groups within molecules to yield isomeric forms

Question 9

Ligases

Answer 9

Class of enzymes that catalyzes the formation of C-C, C-S, C-O, and C-N bonds by condensation reactions coupled to cleavage of ATP (or similar cofactor).

Question 10

Active site

Answer 10

The pocket on the enzyme where the substrate molecule binds, and where the chemical transformation occurs.

Question 11

Substrate

Answer 11

Molecule that binds to an enzyme’s active site.

Question 12

Transition state

Answer 12

“A fleeting molecular moment” when both going back to substrate state or going on to product state are equally probable.

Question 13

Activation energy

Answer 13

The energy barrier required for molecules to overcome in order to reach product state. Enzymes will lower activation energy to increase reaction rates.

Question 14

Reaction intermediate

Answer 14

A transient chemical species that exists in the reaction pathway, and has finite chemical lifetime.

Question 15

Rate-limiting step

Answer 15

The step(s) with the highest activation energy.

Question 16

Binding energy

Answer 16

The energy derived from enzyme-substrate binding, often used by enzymes to lower the reaction’s activation energy.

Question 17

Lock-and-key model

Answer 17

The idea that enzymes were structurally complementary to their substrates –> fit together like a lock and key. This model is misleading, though.

Question 18

General acid-base catalysis

Answer 18

Transfer of protons between enzyme and substrate or intermediate, mediated by weak acids or bases other than water.

Question 19

Specific acid-base catalysis

Answer 19

Transfer of protons, where only H+ and OH- present in water are used

Question 20

Specific acid-base catalysis

Answer 20

Transfer of protons, where only H+ and OH- present in water are used

Question 21

Covalent catalysis

Answer 21

Catalysis where a transient covalent bond between enzyme and substrate is formed. Formation and breakdown of a covalent intermediate.

Question 22

Metal ion catalysis

Answer 22

a

Question 23

Enzyme kinetics

Answer 23

Understanding of enzyme mechanisms by determining the rate of a reaction and how it changes.

Question 24

Saturation effect

Answer 24

a

Question 25

Michaelis-Menten equation

Answer 25

a

Question 26

Michaelis constant

Answer 26

Km

Question 27

Dissociation constant

Answer 27

Kd

Question 28

kcat

Answer 28

turnover number

Question 29

Inhibition

Answer 29

later

Question 30

Reversible inhibition

Answer 30

Competitive, uncompetitive, mixed, and noncompetitive inhibition.

Question 31

Competitive inhibition

Answer 31

A competitive inhibitor molecule competes with the substrate for the active site of enzyme. While the inhibitor is bound to the enzyme, the substrate cannot bind. Apparent Km increases while there is no effect on Vmax.

Question 32

Apparent Km

Answer 32

a

Question 33

Uncompetitive inhibition

Answer 33

An uncompetitive inhibitor binds at site distinct from active site, and binds only to the enzyme-substrate complex (so substrate does bind to enzyme). Lowers Vmax, and lowers apparent Km

Question 34

Mixed inhibition

Answer 34

A mixed inhibitor binds at a site distinct from active site, but can bind to either the free enzyme or the enzyme-substrate complex. Usually affects both Km and Vmax.

Question 35

Noncompetitive inhibition

Answer 35

affects Vmax but not Km.

Question 36

Irreversible inhibition

Answer 36

An irreversible inhibitor binds covalently with or destroys a functional group on an enzyme that is essential for that enzyme’s activity. There are suicide inactivators and transition-state analogs.

Question 37

Suicide inactivator

Answer 37

An inhibitor (irreversible) that binds to active site and starts the normal reaction, but does not go to the normal product. Instead, its converted into a very reactive compound that combines irreversibly with the enzyme, and effectively inactivate the enzyme.

Question 38

Transition-state analogs

Answer 38

These molecules are implemented/designed to resemble the transition state. They bind to the enzyme more tightly than the substrate in the enzyme-substrate complex because they fit into the active site better

Question 39

Chymotrypsin

Answer 39

A protease, which catalyzes the hydrolytic cleavage of peptide bonds.This one is specific to bonds adjacent to aromatic AAs.