Enzymes 1

Question 1

What is an enzyme?

Answer 1

• Globular protein

- Biological catalyst

Question 2

What does an enzyme do?

Answer 2

• Catalyses very high reaction rates
• Shows great reaction specificity
• Work in mild temp/pH conditions
• Can be regulated

Question 3

Ribozyme

Answer 3

Catalytic RNA molecule with no protein component

Question 4

Cofactor

Answer 4

Non-protein component needed for activity

Question 5

Coenzyme

Answer 5

Complex organic molecule, usually produced from a vitamin

Question 6

Prosthetic group

Answer 6

Cofactor covalently bound to the enzyme or very tightly associated with the enzyme

Question 7

Apoenzyme

Answer 7

The protein component of an enzyme that contains a cofactor

Question 8

Holoenzyme

Answer 8

The apoenzyme plus the cofactor(s)

Question 9

Substrate

Answer 9

Molecule acted on by the enzyme

Question 10

Active Site

Answer 10

Part of the enzyme in which the substrate binds and is acted upon

Question 11

Class 1

Oxidoreductases

Answer 11

Transfers e

Question 12

Class 2

Transferases

Answer 12

Group transfers

Question 13

Class 3

Hydrolases

Answer 13

Hydrolysis

Question 14

Class 4

Lyases

Answer 14

Form, or add groups to double bonds

Question 15

Class 5

Isomerases

Answer 15

Transfer groups within molecules

Question 16

Class 6

Ligases

Answer 16

Formation of C-C, C-S, C-O, and C-N bonds

Question 17

What do enzymes not do?

Answer 17

• Move reaction equilibria

- Make a non-spontaneous reaction spontaneous

Question 18

What can enzymes do?

Answer 18

• Increase rate of spontaneous reaction
• Lower the activation energy of biochemical reactions
• Accelerate movement towards reaction equilibrium

Question 19

What is Gibbs free energy?

Answer 19

Useful energy generated from cellular reactions

Question 20

What is true of spontaneous reactions?

Answer 20

They must have -ve ΔG value as they will decrease enthalpy and/or increase entropy

Question 21

What is the energy barrier equal to?

Answer 21

Energy required to position chemical groups correctly

Question 22

What does the transition state represent?

Answer 22

The moment that chemical bonds are formed and broken

Question 23

Binding energy

Answer 23

When enzymes for non-covalent bonds with substrate molecules allowing them to take the reaction through a different path of reaction intermediates

Question 24

What must the active site be complementary to in order for a reaction to take place?

Answer 24

Transition state

Question 25

What 3 ways do enzymes reduce activation energy?

Answer 25

- Entropy reduction - Desolvation - Induced fit

Question 26

How does entropy reduction reduce activation energy?

Answer 26

- Molecules in free solution will only react by bumping into one another - Enzymes force the substrate to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed

Question 27

How does desolvation reduce activation energy?

Answer 27

Weak bonds between the substrate and enzyme essentially replace most or all of the H bonds between substrate and aqueous solution

Question 28

How does induced fit reduce activation energy?

Answer 28

Conformational changes occur in the protein structure when the substrate binds

Question 29

How can an enzyme by analysed?

Answer 29

- Enzyme kinetics - Mutagenesis - 3D structure

Question 30

Why does Vmax occur when you increase the amount of substrate?

Answer 30

All of the enzyme active sites are saturated with substrate

Question 31

What is critical to the Michaelis-Menten equation?

Answer 31

Formation of an enzyme-substrate complex

Question 32

What does the model state?

Answer 32

- The first part of the reaction (to produce ES) occurs reversibly - Second part of the equation (to produce E and P) occurs more slowly than the first part

Question 33

What assumptions are made with the Michaelis-Menten equation?

Answer 33

- If 2nd part is slower it must limit the rate of the overall reaction so the overall rate of reaction must be proportional to the amount of ES - More ES would give a higher overall reaction rate and less would give a slower overall reaction rate

Question 34

What is the M-M equation?

Answer 34

Vo= Vmax[S] ------------ Km+ [S]

Question 35

What is the M-M equation consistent with?

Answer 35

The experimentally observed dependence of Vo on [S] with the curves shape depending on Vmax/Km at low [S] and depeding on Vmax at high [S]

Question 36

Define Km.

Answer 36

Km is equivalent to the substrate concentration at which the initial reaction rate is half of the maximum reaction rate

Question 37

What do larger Km values indicate?

Answer 37

A less stable ES complex

Question 38

What do smaller Km values indicate?

Answer 38

A more stable ES complex