Lecture 6

Question 1

What are enzymes?

Therefore, what do enzymes increase?

Answer 1

Biological catalysts.

Increase reaction rate.

Question 2

How many enzymes are proteins?

Answer 2

Most, but not all.

Question 3

An example of an enzyme with low specificity?

Where is it found, and what does it act on?

Answer 3

Subtilisin.

Bacterial protease that cleaves peptide bonds indiscriminately.

Question 4

An example of an enzyme with medium specificity?

Where is it found, and what does it act on?

Answer 4

Trypsin.

Digestive enzyme cleaves peptide bonds on carboxyl side of Lys or Arg.

Question 5

An example of an enzyme with high specificity?

Where is it found, and what does it act on?

Answer 5

Thrombin.

Blood clotting enzyme cleaves between Arg and Gly within specific amino acid sequence motifs.

Question 6

Although most enzymes end in -ase, what group are a general exception and what do they end in?

Answer 6

Proteolytic enzymes. End in -in.

Question 7

What is the name of the International Union of Biochemistry and Molecular Biology’s method of classifying enzymes?

Answer 7

The enzyme classification system.

Question 8

How does the Enzyme Classification System work?

Answer 8

4 digits: 1.2.3.4
1st digit from 6 major classes.
2nd and 3rd digits give further details for type of reaction.
4th digit gives substrate.

Question 9

What class does 1 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 9

Oxidoreductases.

Transfer of electrons (hydride ions or H atoms).

Question 10

What class does 2 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 10

Transferases.

Group-transfer reactions.

Question 11

What class does 3 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 11

Hydrolases.
Hydrolysis reactions (transfer of functional groups to water).

Question 12

What class does 4 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 12

Lysases.

Addition of groups to double bonds, or formation of double bonds by removal of groups.

Question 13

What class does 5 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 13

Isomerases.

Transfer of groups within molecules to yield isomeric forms.

Question 14

What class does 6 stand for in the 1st digit of the ECS?
What type of reaction occurs?

Answer 14

Ligases.

Formation of C-C, C-S, C-O, C-N bonds by condensation reactions coupled to ATP cleavage.

Question 15

What is the rate of reaction?

Answer 15

Amount of product produced per unit time.

Question 16

What is the SI measurement for enzyme activity, and what’s its definition?

Answer 16

Katal (kat) (moles/sec).

The amount of an enzyme that converts 1 mol of substrate per second under standard assay conditions.

Question 17

What is an alternative measurement to the SI system for enzyme activity, and what’s its definition?

Answer 17

International activity unit (U) (μmoles/min).
An amount of enzyme that will catalyse the transformation of 1 micromole of the substrate per minute under standard assay conditions.

Question 18

What is the equation for K?

Answer 18

Kfor/Krev.

Question 19

What type of reactions release energy to surroundings?

Answer 19

Exergonic reactions.

Question 20

What type of reactions require an overall input of energy?

Answer 20

Endogonic reactions.

Question 21

What is the activation energy?

Answer 21

The amount of energy necessary to push the reactants over an energy barrier.

Question 22

What is the ΔG?

Answer 22

Difference between the free energy of the products and the free energy of the reactants.

Question 23

What is the name of the summit of an activation energy curve?

Answer 23

The transition state (molecules at an unstable point).

Question 24

What is the shorthand for the difference between free energy of the reactants and transition state?

Answer 24

ΔG‡ (Gibbs free energy of activation).

Question 25

What two symbols can represent the initial input of energy into a system?

Answer 25

ΔG‡ (Gibbs free energy of activation), or EA (activation energy).

Question 26

How does the activation energy cause a reaction?

Answer 26

Increases speed of reactant molecules, creates more powerful collisions, thereby making the reactants unstable.

Question 27

Does ΔG tell us whether a reaction will occur?

Answer 27

Yes.

Question 28

Does ΔG tell us if a reaction will happen at a significant rate?

Answer 28

No.

Question 29

Is ΔG‡ limiting?

Answer 29

Yes.

Question 30

Is the thermal energy provided by room temperature always enough to reach the transition state?

Answer 30

No, only sometimes.

Question 31

If ΔG‡ is significant, an input of energy is required. Why?

Answer 31

To drive the reaction forward to approach equilibrium at a faster rate.

Question 32

How do enzymes speed up reactions?

Answer 32

By lowering EA, enabling transition states to be reached even at moderate temperatures.

Question 33

Do enzymes change ΔG?

Answer 33

No. Hasten reactions that would occur eventually.

Question 34

Do enzymes affect the backwards rates to the same extent as the forwards rates?

Answer 34

Yes.

Question 35

Why would an enzyme complementary to the substrate not be useful?

Answer 35

The combination of both is more stable than the stick alone.

Question 36

Why are enzymes complementary to the transition state?

Answer 36

Enzymes bind optimally to transition state, so minimum of activation energy required.

Question 37

What is the first step in catalysis, the formation of a(n)...?

Answer 37

Enzyme substrate complex.

Question 38

How do enzymes work as catalysts?

Answer 38

Bring substrates together in favourable orientations to promote the formation of the transition state.

Question 39

Why is the lock and key model good?

Answer 39

Explains substate specificity.

Question 40

Why is the lock and key model flawed?

Answer 40

From energetic point of view, won't work if best fit is with native form of substrate.

Question 41

Who invented the lock and key method, and when?

Answer 41

Emil Fischer. 1890.