Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are biological catalysts.

Question 2

How are enzymes named?

Answer 2

By adding the suffix -ase to the substrate that they catalyse e.g. urease

Question 3

What are the classification of enzymes?

Answer 3

Hydrolases - hydrolysis reactions
isomerases - transfer of groups within a molecule
ligases or synthases - bond formation coupled by ATP hydrolysis

Question 4

How do enzymes increase the reaction rate?

Answer 4

Enzymes lower the activation energy by binding the substrate and forming an enzyme-substrate complex

Question 5

What is the mechanism of an enzyme with a substrate?

Answer 5

An enzyme is specific - binds to only one substrate. It is a lock and key mechanism.

Question 6

How do enzymes decrease the activation energy?

Answer 6

The enzymes hold the substrates at certain positions and angles to improve the reaction rate. Enzymes formation of an enzyme-substrate complex cause slight changes in the 3D shape which can also promote activity. In multisubstrate enzyme-catalysed reactions (enzymes with more than one active site) enzyme can hold substrate so that reactive regions of substrates are close to each other (proximity effect).

Question 7

How does the enzyme activity change with temperature?

Answer 7

As the temperature increases up to a certain limit, the rate of enzyme catalysed reactions increase. This is because the number of successful collisions and the number of molecules with sufficient activation energy increases. Beyond this limit, the enzyme activity decreases with temperature.

Question 8

What causes the enzyme activity to decrease above a certain temperature?

Answer 8

The enzyme becomes denatured. The active site will change shape and can no longer bind to the specific substrate.

Question 9

Up until the peak of enzyme activity, what is the equation for the rate of enzyme conversion of substrate?

Answer 9

Vm = k2 * E0

Question 10

What is the rate of enzyme conversion above this temperature

Answer 10

Vm = k2 * E

Question 11

What is the rate constant given by according to the Arrhenius equation?

Answer 11

k2 = Ae^(-Ea/RT)

Question 12

Does a small rise in temperature affect enzyme activation or enzyme denaturation more?

Answer 12

It will affect Enzyme denaturation much more

Question 13

What are the two reasons for the change of enzyme activity with pH?

Answer 13

• The ionic groups on the active site of the enzyme will change
• The three-dimensional shape of the enzyme will change

Question 14

Is the activity of enzymes limited by the pH?

Answer 14

Yes, there is an optimum pH at which an enzyme will function

Question 15

What is enzyme immobilisation?

Answer 15

The restriction of enzyme mobility in a fixed space

Question 16

What are the advantages of enzyme immobilisation?

Answer 16

Enzyme reutilisation, elimination of enzyme recovery and purification processes, product purity is usually improved, effluent handling problems are minimised by immobilisation

Question 17

Why is catalyst reuse critical for many processes?

Answer 17

Enzymes are expensive

Question 18

For which enzymes in the body are immobilised membranes a good model system?

Answer 18

Some intracellular enzymes are membrane bound, the enzymes in this process are able to mimic and understand the action of membrane-bound intracellular enzymes.

Question 19

Disadvantages of immobilised enzymes

Answer 19

Many immobilised enzymes exhibit lower activity compared to free enzymes, more expensive to prepare than free enzymes, mass transfer limitations due to immobilisation methods

Question 20

The two categories of immobilisation

Answer 20

• Entrapment (Matrix-Entrapped and Membrane- Entrapped)

- Bound (Adsorbed and Covalently Bound)

Question 21

What is matrix entrapment?

Answer 21

The enzyme solution is mixed with polymeric fluid that solidifies into various forms, depending on application. The polymeric fluid is semi-permeable. Large molecular weight enzymes cannot diffuse out, but smaller substrate and product molecules can

Question 22

Give some examples for matrices fro enzyme entrapment

Answer 22

Agar, polyacrylamide, collagen

Question 23

What is membrane entrapment?

Answer 23

Enzyme solutions may be confined between thin semi-permeable membranes.

Question 24

Give some examples of membrane materials

Answer 24

Nylon, cellulose, polyacrylate

Question 25

What is surface adsorption?

Answer 25

The attachment of enzymes to stationary solids by weak physical forces e.g. van der Waals forces. The active site of the enzyme is normally unaffected and nearly full activity is observed

Question 26

What is surface immobilisation by covalent bonding?

Answer 26

The retention of enzyme on support surfaces by covalent bonding between functional groups on the enzyme and those on the support surface.

Question 27

What are the functional groups on the enzyme?

Answer 27

amino, carboxyl, hydroxyl, sulfhydryl

Question 28

What is the condition for the surface immobilisation by covalent bonding on the enzyme?

Answer 28

The active site cannot participate in covalent bonding

Question 29

How can the covalent bonding of the active site to the immobilisation surface be prevented?

Answer 29

Enzyme inhibitors can be used.

Question 30

Why are there diffusional limitations on immobilised enzyme systems?

Answer 30

The substrate must diffuse from the bulk solution up to the surface of the immobilised enzyme prior to reaction.

Question 31

What is the Damkohler number?

Answer 31

Da = maximum rate of reaction/ maximum rate of diffusion = (Vm/ kL[Sb})
where kL is the mass transfer coefficient
[Sb] is the substrate concentration in bulk liquid

Question 32

Why is Damkohler number important?

Answer 32

Determines whether limitations on intrinsic enzyme kinetics are observed or not

Question 33

What happens if Da»1 ?

Answer 33

Diffusion rate is limiting the observed rate.

Question 34

What happens if Da«1?

Answer 34

The reaction rate is limiting, the observed rate is not being affected by rate of diffusion.