Study Guide

Immobilised enzymes

CIE A-Level BiologyΒ· 25 min read

1. Definition and methods of immobilisationβ˜…β˜…β˜†β˜†β˜†β± 10 min

πŸ“˜ Definition

Immobilised enzymes

Enzymes that are bound to an inert, insoluble supporting material, rather than being free in solution. This separates the enzyme from the reaction mixture containing substrate and product.

Example:

Lactase enzyme trapped in alginate beads to produce lactose-free milk

  • Adsorption: Enzymes bind non-covalently to the external surface of an inert support (e.g. glass beads, activated charcoal, ion-exchange resin)

  • Covalent bonding: Enzymes covalently bond to a solid support via amino acid R-groups, very low enzyme leakage

  • Entrapment: Enzymes trapped within the porous matrix of a gel (e.g. alginate gel, polyacrylamide gel) or microcapsules

  • Membrane confinement: Enzymes separated from substrate solution by partially permeable membranes

πŸ“ Worked Example

A biotechnologist wants to produce lactose-free milk on an industrial scale. They need a low-cost method that has minimal enzyme leakage into the final product. Which method of immobilisation is most appropriate, and why?

  1. 1
    1. First identify the key requirements: low production cost and minimal enzyme leakage into the final milk product.
  2. 2
    1. Entrapment in alginate beads is the most appropriate method, for two key reasons:
  3. 3
    • Alginate is very low cost, making it suitable for large scale industrial use
  4. 4
    • Enzymes are trapped within the gel matrix, so leakage into the final milk product is minimal
  5. 5
    1. Other methods are less suitable: adsorption is low cost but has high leakage, while covalent bonding has low leakage but is very expensive for large scale production.

Exam tip:

CIE commonly asks you to name and describe one method of immobilisation, so memorise one method (e.g. entrapment in alginate) in detail.

2. Advantages over free enzymesβ˜…β˜…β˜†β˜†β˜†β± 10 min

Immobilised enzymes have several key benefits that make them more useful than free enzymes for most industrial and commercial applications:

  • Easy product separation: Enzymes remain bound to the support, so they can be easily removed from the final product with no contamination, eliminating the need for expensive downstream purification

  • Reusability: Immobilised enzymes can be reused multiple times, significantly reducing overall production costs

  • Increased stability: Binding to a support stabilises the enzyme's tertiary structure, so immobilised enzymes are more resistant to changes in pH and temperature, giving them a longer working life

  • Continuous processing: They can be used in continuous flow production systems, which are more efficient than batch processing with free enzymes

πŸ“ Worked Example

Explain why immobilised enzymes are preferred to free enzymes for industrial production of high-fructose corn syrup.

  1. 1
    1. High-fructose corn syrup is produced in large, continuous batches using the enzyme glucose isomerase.
  2. 2
    1. Immobilised glucose isomerase can be reused for hundreds of production runs, cutting the cost of buying new enzyme for every batch.
  3. 3
    1. The enzyme does not contaminate the final syrup product, so expensive purification steps to remove free enzyme are not required.
  4. 4
    1. Immobilised glucose isomerase also has higher temperature stability than free enzyme, allowing the reaction to run at higher rates for longer.

3. Disadvantages of immobilised enzymesβ˜…β˜…β˜…β˜†β˜†β± 10 min

Immobilised enzymes are not optimal for all applications, and have several key drawbacks compared to free enzymes:

  • Higher initial cost: Immobilisation requires additional processing and supporting materials, leading to higher upfront production costs

  • Reduced enzyme activity: The immobilisation process can alter the shape of the enzyme's active site, leading to lower overall activity than free enzyme

  • Diffusion barrier: Substrate has to diffuse through the support material to reach the enzyme, leading to slower overall reaction rates

  • Contamination risk: Microbes can grow on the organic support material, leading to contamination of the reaction mixture and product

πŸ“ Worked Example

A small pharmaceutical company wants to produce one small batch of a pure medical protein. Explain why they might choose free enzymes instead of immobilised enzymes.

  1. 1
    1. For a single small batch of product, the high upfront cost of immobilising the enzyme is not economically viable.
  2. 2
    1. Free enzymes have higher activity and faster reaction rates for small scale production, because there is no diffusion barrier for substrate to reach the enzyme.
  3. 3
    1. The cost of purifying the final product to remove free enzyme is much lower than the cost of immobilising the enzyme for a single use.

4. Common applicationsβ˜…β˜…β˜†β˜†β˜†β± 10 min

Immobilised enzymes are widely used across food production, biotechnology and medical diagnostics. You are expected to recall at least one named example for CIE exams.

  • Lactose-free milk: Immobilised lactase breaks down lactose into glucose and galactose, producing milk suitable for people with lactose intolerance

  • High-fructose corn syrup: Immobilised glucose isomerase converts glucose to fructose, a common sweetener in processed foods

  • Blood glucose test strips: Immobilised glucose oxidase is bound to test strips to measure blood glucose levels for people with diabetes

  • Biological washing powders: Some formulations use immobilised proteases and lipases that do not contaminate wastewater

πŸ“ Worked Example

Describe how immobilised enzymes are used in blood glucose testing.

  1. 1
    1. Blood glucose test strips have the enzyme glucose oxidase immobilised on the strip surface.
  2. 2
    1. When a drop of blood is added to the strip, glucose from the blood diffuses to the immobilised enzyme.
  3. 3
    1. Glucose oxidase catalyses the oxidation of glucose, producing a product that triggers an electrochemical change measured by the glucose meter.
  4. 4
    1. The enzyme remains bound to the strip, so it does not interfere with the measurement, and the strip can be safely discarded after use.

Exam tip:

Always include a specific named example of a use when asked, CIE examiners award marks for specific examples.

5. Common Pitfalls

Wrong move:

Stating that immobilised enzymes never leach into the product mixture.

Why:

Some methods of immobilisation, especially adsorption, have moderate levels of enzyme leakage.

Correct move:

State that immobilised enzymes have far lower leakage than free enzymes, so contamination is minimal, but leakage can vary by method.

Wrong move:

Claiming immobilised enzymes are always cheaper than free enzymes for all applications.

Why:

Immobilisation has high upfront costs that are only offset when enzymes are reused many times. For small single batches, free enzymes are cheaper.

Correct move:

Immobilised enzymes are cheaper for large scale continuous production due to reusability, but more expensive for small single batches.

Wrong move:

Confusing entrapment with covalent bonding as an immobilisation method.

Why:

Entrapment does not involve covalent bonding between the enzyme and the support material.

Correct move:

Entrapment traps enzymes within the porous matrix of a gel like alginate, no covalent bonds are required.

Wrong move:

Claiming that immobilised enzymes have lower stability than free enzymes.

Why:

Binding to a support stabilises the enzyme's tertiary structure, so most immobilised enzymes are more stable.

Correct move:

Immobilised enzymes generally have higher stability to changes in pH and temperature than free enzymes.

6. Quick Reference Cheatsheet

Feature

Immobilised enzymes

Free enzymes

Reusability

Yes, multiple uses

No, cannot be recovered

Product contamination

Minimal/Low

High

Upfront cost

Higher

Lower

Reaction rate

Slower (diffusion barrier)

Faster

pH/temperature stability

Higher

Lower

B

e

s

t

f

o

r

L

a

r

g

e

s

c

a

l

e

c

o

n

t

i

n

u

o

u

s

p

r

o

d

u

c

t

i

o

n

,

d

i

a

g

n

o

s

t

i

c

s

S

m

a

l

l

s

c

a

l

e

s

i

n

g

l

e

b

a

t

c

h

p

r

o

d

u

c

t

i

o

n

When this came up on past exams

AI-estimated based on syllabus patterns β€” cross-check with official past papers for accuracy. Use only as revision-focus signals.

  • 2022 Β· 2

    Describe one method of enzyme immobilisation

  • 2021 Β· 1

    MCQ: Advantage of immobilised enzymes

  • 2023 Β· 4

    Evaluate use in industrial production