Enzymes

Question 1

Define enzyme

Answer 1

An enzyme is a globular protein which acts as a biological catalyst by speeding up the rate of a chemical reaction

Question 2

Define substrate

Answer 2

The substances that enzymes convert into products in biochemical reactions are called substrates

Question 3

Define active site

Answer 3

The active site is the special region on the surface of the enzyme which substrate molecules bind to and convert into products

Question 4

How are enzymes specific?

Answer 4

The active site and the substrate complement each other in terms of both shape and chemical properties and hence only a specific substrate is capable of binding to a particular enzyme’s active site

Question 5

Are enzymes reusable?

Answer 5

Enzymes are not changed or consumed by the reactions they catalyse and thus can be reused

Question 6

Explain how enzyme catalysis (activity) is carried out?

Answer 6

1. When a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed
2. The enzyme catalyses the conversion of the substrate into product while bounded to the active site, creating an enzyme-product complex
3. The enzyme and product then dissociate – as the enzyme was not consumed, the active site is vacant for substrates to bind again

Question 7

What does Enzyme catalysis require?

Answer 7

Enzyme catalysis requires that the substrate be brought into close physical proximity with the active site.

Question 8

What is collision in terms of enzyme activity?

Answer 8

The coming together of a substrate molecule and an active site is known as collision

Question 9

State the requirement needed for enzyme substrate collisions

Answer 9

Enzyme-substrate collisions occur via the molecular motion of enzymes and substrates dissolved in liquid water

Question 10

Describe how enzyme substrate collisions take place

Answer 10

The molecules of water in the liquid state are in contact with each other yet are able to show some degree of free movement and move past each other. The motion of liquid molecules of water is random and therefore collisions between substrate molecules and active occur due to random movement of the two dissolved in water.

Question 11

What are successful collisions?

Answer 11

Successful collisions occur when the substrate and active site are correctly aligned to allow binding to take place

Question 12

How can the rate of enzyme catalysis (activity) can be increased?

Answer 12

The rate of enzyme catalysis can be increased by improving the frequency of collisions via:

Increasing the molecular motion of the particles (thermal energy can be introduced to increase kinetic energy)
Increasing the concentration of particles (either substrate or enzyme concentrations)

Question 13

How is the activity of an enzyme affected by various factors?

Answer 13

Various factors may affect the activity of enzymes, by either affecting the frequency of enzyme-substrate collisions or by affecting the capacity for the enzyme and substrate to interact (e.g. denaturation)

Question 14

Explain enzyme specificity in terms of denaturation

Answer 14

The shape and chemical properties of the active site are highly dependent on the tertiary structure of the enzyme

Like all proteins, enzyme structure can be modified by external factors such as high temperatures and extreme pH

These factors disrupt the chemical bonds which are necessary to maintain the tertiary structure of the enzyme
Any change to the structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate

Question 15

Explain the effect of substance concentration on rate of enzyme activity

Answer 15

Increasing substrate concentration will increase the activity of a corresponding enzyme
More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period
After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels
This is because the environment is saturated with substrate and all enzymes are bound and reacting (Vmax)

Question 16

What are immobilised enzymes?

Answer 16

Immobilised enzymes have been fixed to a static surface in order to improve the efficiency of the catalysed reaction

Question 17

List the use of immobilised enzymes in the industry

Answer 17

Immobilised enzymes are utilised in a wide variety of industrial practices:

Biofuels – Enzymes are used to breakdown carbohydrates to produce ethanol-based fuels
Medicine – Enzymes are used to identify a range of conditions, including certain diseases and pregnancy
Biotechnology – Enzymes are involved in a number of processes, including gene splicing
Food production – Enzymes are used in the production and refinement of beers and dairy products
Textiles – Enzymes are utilised in the processing of fibres (e.g. polishing cloth)
Paper – Enzymes assist in the pulping of wood for paper production

Question 18

Advantages of enzyme immobilisation

Answer 18

Enzyme concentrations are conserved as the enzyme is not dissolved – hence it can be retained for reuse
Separation of the product is more easily achieved as the enzyme remains attached to the static surface
Concentration of enzyme can be increased as the enzyme is not dissolved- increasing rate of reaction
Stability of the enzyme to changes in temperature and pH is increased, reducing rate of degradation of the enzyme, resulting in cost saving

Question 19

Common ways of immobilising enzymes

Answer 19

Aggregations of enzymes bonded together
Attachment of enzyme to a surface for example glass
Entrapped in gels ie. alginate gel beads

Question 20

How is lactose free milk produced?

Answer 20

Lactose-free milk can be produced by treating the milk with the enzyme lactase

The lactase is purified from yeast or bacteria and then bound to an inert substance (such as alginate beads)
Milk is then repeatedly passed over this immobilised enzyme, becoming lactose-free

Question 21

Advantages of lactose free dairy products

Answer 21

The generation of lactose-free milk can be used in a variety of ways:

As a source of dairy for lactose-intolerant individuals
As a means of increasing sweetness in the absence of artificial sweeteners (monosaccharides are sweeter tasting)
As a way of reducing the crystallisation of ice-creams (monosaccharides are more soluble, less likely to crystalise)
As a means of reducing production time for cheeses and yogurts (bacteria ferment monosaccharides more readily)