2.5

Question 1

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

enzymes are not…

Answer 2

changed or consumed by the reactions they catalyse and thus can be reused

Question 3

enzymes are typically named after…

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

Active Site

Answer 4

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

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

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

Question 5

enzymes reactions typically occur in…

Answer 5

aqueous solutions (e.g. cytoplasm, interstitial fluid, etc.)

Consequently, the substrate and enzyme are usually moving randomly within the solution (Brownian motion)
Sometimes an enzyme may be fixed in position (e.g. membrane-bound) – this serves to localise reactions to particular sites

Question 6

Enzyme Catalysis

Answer 6

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

• When a substrate binds to the enzyme’s active site, an enzyme-substrate complex is formed
• The enzyme catalyses the conversion of the substrate into product, creating an enzyme-product complex
• The enzyme and product then dissociate – as the enzyme was not consumed, it can continue to catalyse further reactions

Question 7

Collision Frequency

Answer 7

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 8

active site

Answer 8

All enzymes possess an indentation or cavity to which the substrate can bind with high specificity

Question 9

Like all proteins, enzyme structure can be modified by external factors such as

Answer 9

high temperature and 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 10

temperature and enzymes

Answer 10

• Low temperatures result in insufficient thermal energy for the activation of an enzyme-catalysed reaction to proceed
• Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity
• This is because a higher kinetic energy will result in more frequent collisions between the enzymes and substrates
• At an optimal temperature (may vary for different enzymes), the rate of enzyme activity will be at its peak
• Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the enzyme’s hydrogen bonds
• This causes the enzyme (particularly the active site) to lose its shape, resulting in the loss of activity (denaturation)

Question 11

pH

Answer 11

• Changing the pH will alter the charge of the enzyme, which in turn will alter protein solubility and overall shape
• Changing the shape or charge of the active site will diminish its ability to bind the substrate, abrogating enzyme function
• Enzymes have an optimal pH (may differ between enzymes) and moving outside this range diminishes enzyme activity

Question 12

Substrate concentration

Answer 12

• 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 13

When designing an experiment to test the effect of factors affecting enzyme activity, the three key decisions to be made are:

Answer 13

• 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 14

The main factors which will affect the activity of an enzyme on a given substrate are:

Answer 14

• 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 15

Immobilised enzymes

Answer 15

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

Question 16

immobilised enzymes concentrations and separation

Answer 16

• 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 17

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

Answer 17

Biofuels, Medicine, Biotechnology, Food production, Textiles and Paper

Question 18

biofuels

Answer 18

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

Question 19

medicine

Answer 19

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

Question 20

biotechnology

Answer 20

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

Question 21

food productions

Answer 21

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

Question 22

textiles

Answer 22

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

Question 23

paper

Answer 23

Enzymes assist in the pulping of wood for paper production

Question 24

Lactose

Answer 24

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

Question 25

Lactose intolerance

Answer 25

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

Incidence of lactose intolerance is particularly high in Asian, African and Aboriginal populations
Incidence is lower in European populations (due to a mutation that maintains lactase production into adulthood)

Question 26

Producing Lactose-Free Milk

Answer 26

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 27

Scientists attempting to make lactose-free milk

Answer 27

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 28

Advantages of Lactose-Free Dairy Products

Answer 28

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)