2.5 Enzymes

Question 1

What is an 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

Do enzymes get used up?

Answer 2

No

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

Question 3

How are enzymes named?

Answer 3

Enzymes are typically named after the molecules they react with (called the substrate) and end with the suffix ‘-ase’

For example, lipids are broken down by the enzyme lipase

Question 4

What is the active site?

Answer 4

The active site is the region on the surface of the enzyme which binds to the substrate molecule

Question 5

What is the active site complementary to?

Answer 5

The active site and the substrate complement each other in terms of both shape and chemical properties

Question 6

What does it mean that the active site is complementary to the substrate?

Answer 6

Hence only a specific substrate is capable of binding to a particular enzyme’s active site

Question 7

Where do enzyme reactions typically occur?

Answer 7

Enzyme reactions typically occur in aqueous solutions (e.g. cytoplasm, interstitial fluid, etc.)

Question 8

How do enzymes usually move around?

Answer 8

Consequently, the substrate and enzyme are usually moving randomly within the solution (Brownian motion)

Question 9

Do enzymes always randomly move?

Answer 9

Sometimes an enzyme may be fixed in position (e.g. membrane-bound) – this serves to localise reactions to particular sites

Question 10

What does enzyme catalysis require?

Answer 10

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

Question 11

What is formed when an enzyme and a catalyst collide?

Answer 11

When a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed

Question 12

What is formed once the reaction is catalysed?

Answer 12

The enzyme catalyses the conversion of the substrate into product, creating an enzyme-product complex

Question 13

What happens after the enzyme has catalysed the reaction?

Answer 13

The enzyme and product then dissociate – as the enzyme was not consumed, it can continue to catalyse further reactions

Question 14

How can the rate of enzyme catalysis be increased?

Answer 14

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 15

What is the active site’s specificity dependent on?

Answer 15

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

Question 16

Can enzymes be denatured like proteins?

Answer 16

Yes

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

Question 17

What happens when an enzyme is denatured?

Answer 17

These factors disrupt the chemical bonds which are necessary to maintain the tertiary structure of the enzyme

Question 18

Why are enzymes not able to catalyse reactions after denaturation?

Answer 18

Any change to the structure of the active site (denaturation) will negatively affect the enzyme’s capacity to bind the substrate

Question 19

What may factors affect in order to affect enzyme activity?

Answer 19

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 20

What 3 factors can affect enzyme activity?

Answer 20

Temperature, pH and substrate concentration will all influence the rate of activity of an enzyme

Question 21

How does low temperature affect enzyme activity?

Answer 21

Low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed

Question 22

How does increasing the temperature affect enzyme activity?

Answer 22

Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity

Question 23

Why does increasing temp increase enzyme activity?

Answer 23

This is because a higher kinetic energy will result in more frequent collisions between the enzymes and substrates

Question 24

When will enzyme activity be at its peak? (temp)

Answer 24

At an optimal temperature (may vary for different enzymes), the rate of enzyme activity will be at its peak

Question 25

How does a temp above the enzyme’s optimum affect its activity?

Answer 25

Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds

Question 26

Why is it harmful when the enzymes bonds break?

Answer 26

This causes the enzyme (particularly the active site) to lose its shape, resulting in the loss of activity (denaturation)

Question 27

How will changing the pH affect enzyme activity?

Answer 27

Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape

Question 28

How will changing the pH affect the active site?

Answer 28

Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function

Question 29

At what pH do enzymes function the best?

Answer 29

Enzymes have an optimal pH (may differ between enzymes) and moving outside this range diminishes enzyme activity

Question 30

How does increasing substrate concentration affect enzyme activity?

Answer 30

Increasing substrate concentration will increase the activity of a corresponding enzyme

Question 31

Why does increasing substrate concentration increase enzyme activity?

Answer 31

More substrates mean there is an increased chance of enzyme and substrate colliding and reacting within a given period

Question 32

Does the rate of enzyme increase alongside an increase in substrate concentration?

Answer 32

ONLY INITIALLY

After a certain point, the rate of activity will cease to rise regardless of any further increases in substrate levels

Question 33

Why does enzyme activity reach a plateau even though the concentration of substrate is still increasing?

Answer 33

This is because the environment is saturated with substrate and all enzymes are bound and reacting (Vmax)

Question 34

What 3 variables must be considered when designing an experiment to test the effect of factors on enzyme activity?

Answer 34

Which factor to investigate (i.e. the independent variable)
Which enzyme / substrate reaction to use
How to measure the enzyme activity (i.e. the dependent variable

Question 35

What are the 4 main factors that will affect the activity of an enzyme?

Answer 35

Temperature (use water baths to minimise fluctuations)
pH (acidic or alkaline solutions)
Substrate concentration (choose range to avoid saturation)
Presence of inhibitor (type of inhibitor will be enzyme-specific)

Question 36

What are most reactions measured according to?

Answer 36

The amount / rate of substrate decomposition (e.g. breakdown of starch)
The amount / rate of product formation (e.g. formation of maltose)

Question 37

What type of enzymes are used commonly in the industry? why?

Answer 37

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

Question 38

What are the 2 main reasons for using immobilised enzymes in the industry?

Answer 38

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

Question 39

In what 6 processes can immobilised enzymes be used?

Answer 39

• biofuels
• medicine
• biotechnology
• food production
• textiles
• paper

Question 40

How are enzymes used to create biofuels?

Answer 40

Enzymes are used to breakdown carbohydrates to produce ethanol-based fuels

Question 41

How are enzymes used to create medicine?

Answer 41

Enzymes are used to identify a range of conditions, including certain diseases and pregnancy

Question 42

How are enzymes used in biotechnology?

Answer 42

Enzymes are involved in a number of processes, including gene splicing

Question 43

How are enzymes used in food production?

Answer 43

Enzymes are used in the production and refinement of beers and dairy products

Question 44

How are enzymes used to create textiles?

Answer 44

Enzymes are utilised in the processing of fibres (e.g. polishing cloth)

Question 45

How are enzymes used to create paper?

Answer 45

– Enzymes assist in the pulping of wood for paper production

Question 46

What is lactose? What can break it down?

Answer 46

Lactose is a disaccharide of glucose and galactose which can be broken down by the enzyme lactase

Question 47

Why is lactose-free milk needed?

Answer 47

Historically, mammals exhibit a marked decrease in lactase production after weaning, leading to lactose intolerance

Question 48

Where is incidence of lactose intolerance particularly high?

Answer 48

Incidence of lactose intolerance is particularly high in Asian, African and Aboriginal populations

Question 49

Where is lactose intolerance less common and why?

Answer 49

Incidence is lower in European populations (due to a mutation that maintains lactase production into adulthood)

Question 50

1. How can lactose-free milk be made (general)?

Answer 50

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

Question 51

2. How is the lactase obtained?

Answer 51

The lactase is purified from yeast or bacteria and then bound to an inert substance (such as alginate beads)

Question 52

3. How is the lactase used to create lactose-free milk?

Answer 52

Milk is then repeatedly passed over this immobilised enzyme, becoming lactose-free

Question 53

How are scientists attempting to combat the problem of lactose intolerance?

Answer 53

Scientists are currently attempting to create transgenic cows that produce lactose-free milk

This involves splicing the lactase gene into the cow’s genome so that the lactose is broken down prior to milking

Question 54

What are the 4 main ways in which lactose-free products can be useful?

Answer 54

As a source of dairy for lactose-intolerant individuals
As a means of increasing sweetness in the absence of artificial sweeteners
As a way of reducing the crystallisation of ice-creams
As a means of reducing production time for cheeses and yogurts

Question 55

Why is lactose-free milk sweeter?

Answer 55

broken down into glucose and galactose - monosaccharides are sweeter tasting

Question 56

How does lactose-free dairy products help in reducing crystallisation?

Answer 56

monosaccharides are more soluble, less likely to crystalise

Question 57

How do lactose-free dairy products reduce production time?

Answer 57

bacteria ferment monosaccharides more readily