Enzymes 1

Question 1

What is an enzyme?

Answer 1

A globular protein

Question 2

How does a biological catalyst differ from a chemical catalyst?

Answer 2

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

Question 3

What is a ribozyme?

Answer 3

Catalytic RNA molecules with no protein component

Question 4

What is a cofactor?

Answer 4

Non-protein component needed for activity

Question 5

What is a coenzyme?

Answer 5

Complex organic molecule, usually produced from a vitamin

Question 6

What is a prosthetic group?

Answer 6

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

Question 7

What is an apoenzyme?

Answer 7

The protein component of an enzyme that contains a cofactor.

Question 8

What is a haloenzyme?

Answer 8

The apoenzyme plus the cofactor(s) “whole enzyme”

Question 9

What is a substrate?

Answer 9

Molecule acted on by the enzyme

Question 10

What is the active site?

Answer 10

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

Question 11

What are the 6 classes of enzymes?

Answer 11

Oxidoreductases
Transferases
Hydrolases
Lysases
Isomerases
Ligases

Question 12

What do oxidoreductases do?

Answer 12

Transfer e

Question 13

What do transferases do?

Answer 13

Group transfers

Question 14

What do hydrolases do?

Answer 14

Hydrolysis (transfer chemical groups to water)

Question 15

What do lyases do?

Answer 15

Form, or add groups to double bonds

Question 16

What do isomerases do?

Answer 16

Transfer groups within molecules (form isomers)

Question 17

What do ligases do?

Answer 17

Formation of C-C, C-S, C-O, C-N bonds (coupled to ATP cleavage)

Question 18

What do enzymes not do?

Answer 18

Move reaction equilibria

Make a non-spontaneous reaction spontaneous

Question 19

What do enzyme do?

Answer 19

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

Question 20

What is Gibbs Free-Energy?

Answer 20

“Useful” energy generated from cellular reactions

Question 21

Why must spontaneous reactions have a -ve deltaG value.

Answer 21

They will decrease enthalpy and/or increase entropy

Question 22

Why are spontaneous reactions not instantaneous?

Answer 22

Due to the energy barrier

Question 23

What is the energy barrier?

Answer 23

The energy required to position chemical groups correctly, bond rearrangements, e arrangements etc.

Question 24

What does the transition state show?

Answer 24

The moment that the chemical bonds are formed and broken

Question 25

What can happen once a reaction has reached transition state?

Answer 25

Reactions can then go wither way- revert back to S or change to P

Question 26

What is the binding energy?

Answer 26

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

Question 27

When is a small amount of energy required?

Answer 27

To get past transition state. To get components to bind together To release products from cell.

Question 28

What does the active site have to be complementary to for a reaction to take place?

Answer 28

The transition state

Question 29

How do enzymes reduce activation energy?

Answer 29

Entropy reduction Desolvation Inducced fit

Question 30

What happens in entropy reduction?

Answer 30

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

Question 31

What is desolvation?

Answer 31

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

Question 32

What is induced fit?

Answer 32

Conformational changes occur in the protein structure when the substrate binds

Question 33

How can we analyse an enzyme?

Answer 33

Enzyme kinetics Mutagenesis 3D structure

Question 34

How can enzyme kinetics be measured?

Answer 34

Changing substrate concentration would change the initial rate of a reaction. More substrate= higher initial rate of reaction As the reaction proceeds the substrate is used up and the rate of reaction changes. Initial velocity can be studied if we assume that initial [S] does not change.

Question 35

What response is shown when there is an increase in [S] at low [S]?

Answer 35

Almost linear increase in Vo when graphed

Question 36

What response is shown when there is an increase in [S] at high [S]?

Answer 36

Very little response in Vo

Question 37

Why is there very little response when [S] is increased at high [S]?

Answer 37

Vmax (maximum velocity) occurs because all of the enzyme active sites are saturated with substrate.

Question 38

What does the Michaelis-Menten equation state?

Answer 38

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

Question 39

What assumptions are made about the Michaelis-Menten equation?

Answer 39

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 slower overall reaction rate

Question 40

How is the Michaelis constant calculated?

Answer 40

From the hyperbolic reaction curve as half of the Vmax?

Question 41

What is the M-M equation?

Answer 41

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

Question 42

What is Km?

Answer 42

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

Question 43

What do larger Km values indicate?

Answer 43

A less stable ES complex

Question 44

What do smaller Km values indicate?

Answer 44

A more stable ES complex.

Question 45

What does Vmax tell you?

Answer 45

How fast a reaction is proceeding when the enzyme is saturated with substrate. A measure od the enzymes catalytic rate

Question 46

Why would the Km or Vmax value differ for the same enzyme?

Answer 46

It may function differently in different cells.