Chapter 6 (without enzyme kinetics)

Question 1

What about the makeup of enzymes allows them to carry out very specific reactions?

Answer 1

The 3D structure is designed to fit certain substrates, so only those resulting reactions can take place

Question 2

Without enzymes, the hydrolysis of a peptide bond would take ____ years

Answer 2

20

Question 3

What are the four properties of enzymes that make them the best biocatalysts?

Answer 3

High reaction rates, great specificity, can react in mild conditions, and they can be regulated well

Question 4

If there are many paths available to a reaction, enzymes will choose the ____ favorable one

Answer 4

Most

Question 5

Oxidoreductases catalyze _____ reactions

Answer 5

Oxidation-reduction

Question 6

Transferases catalyze ____

Answer 6

The transfer of functional groups

Question 7

Hydrolases catalyze ______ reactions

Answer 7

Hydrolysis

Question 8

Lyases catalyze ______

Answer 8

The elimination of a group to form a double bone

Question 9

Isomerases catalyze _____

Answer 9

Isomerization

Question 10

Ligases catalyze ____

Answer 10

Bond formation coupled with ATP hydrolysis

ATP has to be USED in the reaction, not just present (ATP –> ADP + P)

Question 11

The three types of bonds utilized in substrate-enzyme binding are:

Answer 11

H-bonding, salt bridges, hydrophobic interactions

Question 12

The substrate refers to the _____

Answer 12

reactant

Question 13

What is the generic purpose of a cofactor?

Answer 13

To assist enzymes in their reactions

Question 14

Compare and contrast cofactors and coenzymes

Answer 14

Cofactors are the overall name of the group and can either be metal ions (Mg2+, Cu2+, Zn2+) or coenzymes

Coenzymes are more complex molecules with different functional groups and can either be bound or unbound to the enzyme

Question 15

When a cofactor is covalently bound to the enzyme it’s called a ______

Answer 15

Prosthetic group

Question 16

If a cofactor participates in a reaction it must be ______ for that reaction to proceed

Answer 16

Regenerated

Question 17

The rate of a reaction is determined by its _____

Answer 17

Activation energy

Question 18

A reaction whose products are lower in energy than their reactants is ______, while a reaction whose products are higher in energy than their reactants is ____

Answer 18

Exergonic

Endergonic

Question 19

Where is the transition state located?

Answer 19

The very highest point of the activation energy

Question 20

ΔGB refers to the ______ energy, which is created by the weak interactions between the enzyme and susbtrate

Answer 20

Binding

Question 21

General acid base catalysis stabilizes intermediates by ____

Answer 21

The transfer of protons to and from the substrate. This is done by a molecule other than water (usually an AA)

Question 22

Covalent bond catalysis occurs when ____

Answer 22

A transient covalent bond forms between the substrate and enzyme, which requires the presence of a sidechain

Usually the nucleophilic group is on the enzyme and the electrophilic group is on the substrate

Question 23

How does entropy reduction help catalyze a reaction?

Answer 23

It decreases the angle from which the substrate can enter the enzyme so it has a higher chance of binding at the proper angle for the reaction to take place. The enzymes also have to be relatively large for this to work

(Less ability to move around lowers the overall entropy)

Question 24

Tunneling has not been verified, but it suspected to help catalyze reactions when _____

Answer 24

Electrons jump back and forth when the enzyme and substrate are far apart from each other

Question 25

What role do metal ions play in metal ion catalysis?

Answer 25

The enzyme holds onto the metal ion to maximize the reaction between it and the substrate

Metal ions can optimize substrate orientation through ionic interactions, mediate redox reactions, stabilize negative charges the develop during the reaction, and polarize some groups

Question 26

Inhibitors often mimic the ______ of the enzyme’s designated substrate and are irreversible because _____

Answer 26

Transition state

They bind so well to the enzyme that they are impossible to remove

Question 27

Why is the enzyme’s active site in the formation of the transition state and not that of the substrate alone?

Answer 27

If the enzyme was in the formation of the substrate, the two would bind too well with each other to overcome the transition state and the reaction would never be completed (products would never form). So, the enzyme is in the shape of the transition state so that it is easier to overcome the activation energy

Question 28

What is the role of the catalytic triad (Ser, His, Asp) in chymotrypsin?

Answer 28

Serine is deprotonated by histidine, which creates a very strong alkoxide ion. Histidine’s pKa is also altered by the proximity of aspartate, which helps to orient His and make it a better proton acceptor