03.01 Enzymes
Definition
- Enzyme: A biological catalyst that speeds up chemical reactions without being consumed.
- Biological as enzymes are proteins
- Catalyst as it remains unchanged after the reaction.
Characteristics of Enzymes
- Globular proteins with specific folding patterns
- Essential for life: Catalyse nearly all metabolic reactions in living organisms
- Naming: Most enzyme names end in -ase (e.g., amylase, ATPase)
Function
- Activation Energy Reduction: Enzymes lower activation energy, allowing reactions to occur faster.
- Example Reaction: Hydrogen peroxide (H₂O₂) decomposition by catalase into water and oxygen.
Case Study: Bombardier Beetle Defence Mechanism
Defence Strategy:
- Uses high-speed enzyme-controlled reactions for a chemical spray attack on predators.
- Mechanism:
- Hydrogen peroxide and hydroquinone mix in a chamber with catalase and peroxidase enzymes.
- Reactions:
- Catalase decomposes hydrogen peroxide to oxygen and water.
- Oxygen oxidizes hydroquinone into quinone.
- Reaction Outcome:
- High heat and gas release.
- Boiling hot spray ejected at predators, creating a loud popping sound and causing predator confusion.
- Beetle escapes.
Experiment – Enzyme Efficiency Comparison
Objective: Test different catalysts on the rate of hydrogen peroxide decomposition to water and oxygen.
- Reaction speed observed via “fizziness” or frothing from oxygen bubbles.
Catalysts Tested:
- Inorganic Catalysts: Iron filings, manganese dioxide
- Biological Catalysts:
- Commercial catalase (pure enzyme)
- Liver and potato pieces (natural sources of catalase)
Results:
- Efficiency Order:
- Catalase (pure) > Liver > Potato > Inorganic catalysts
- Ground-up liver more efficient than liver pieces (increased surface area)
Explanation:
- Biological catalysts (catalase) more effective than inorganic ones due to specific enzyme-substrate binding.
- Pure catalase most efficient due to high enzyme concentration.
- Liver and potato contain catalase, but liver is more concentrated than potato.
- Ground liver offers more surface area, increasing reaction rate.
Types of Enzymes by Location
- Intracellular enzymes: Operate within cells.
- Extracellular enzymes: Secreted to work outside cells.
- Example: Digestive enzymes in the gut.
- Fungi often secrete enzymes externally to digest surrounding food.
Practise Questions
1. Define an enzyme and explain why it is classified as a biological catalyst. (3 marks)
Mark Scheme:
- Enzyme: A biological catalyst that speeds up chemical reactions without being consumed (1).
- Biological: Enzymes are proteins (1).
- Catalyst: Remains unchanged after the reaction (1).
2. Describe two characteristics of enzymes. (2 marks)
Mark Scheme:
- Globular proteins with specific folding patterns (1).
- Essential for life as they catalyse nearly all metabolic reactions in living organisms (1).
3. Most enzyme names end with the suffix ‘-ase.’ Give two examples and state their specific functions. (2 marks)
Mark Scheme:
- Amylase: Breaks down starch into maltose (1).
- ATPase: Hydrolyses ATP into ADP and inorganic phosphate (1).
4. Explain how enzymes lower the activation energy of a reaction. (2 marks)
Mark Scheme:
- Enzymes provide an alternative reaction pathway (1).
- This pathway has a lower activation energy, allowing reactions to occur faster (1).
5. Using the Bombardier beetle as an example, describe how enzymes aid in its defence mechanism. (4 marks)
Mark Scheme:
- Enzymes catalase and peroxidase are used (1).
- Catalase decomposes hydrogen peroxide into oxygen and water (1).
- Oxygen oxidizes hydroquinone into quinone (1).
- This produces heat, gas, and a boiling hot spray to confuse predators (1).
6. In an experiment comparing enzyme efficiency, what was the order of effectiveness of catalysts for decomposing hydrogen peroxide? Explain the results. (4 marks)
Mark Scheme:
- Order of efficiency: Catalase (pure) > Liver > Potato > Inorganic catalysts (1).
- Pure catalase is most efficient due to high enzyme concentration (1).
- Liver contains more catalase than potato, hence faster reaction (1).
- Ground liver has more surface area, increasing reaction rate (1).
7. Differentiate between intracellular and extracellular enzymes, providing an example of each. (4 marks)
Mark Scheme:
- Intracellular enzymes operate within cells (1), e.g., DNA polymerase (1).
- Extracellular enzymes are secreted to work outside cells (1), e.g., digestive enzymes like amylase (1).
8. Why are biological catalysts (enzymes) generally more efficient than inorganic catalysts? (3 marks)
Mark Scheme:
- Enzymes have specific active sites for enzyme-substrate binding (1).
- This specificity increases reaction efficiency (1).
- Inorganic catalysts lack this specific binding mechanism (1).
9. Explain how increasing the surface area of liver affects the rate of reaction in the decomposition of hydrogen peroxide. (3 marks)
Mark Scheme:
- Ground liver provides a larger surface area (1).
- More catalase molecules are exposed to the substrate (1).
- This increases the rate of the reaction (1).
10. Explain why fungi secrete extracellular enzymes and how this benefits them. (3 marks)
Mark Scheme:
- Fungi secrete extracellular enzymes to digest food externally (1).
- Large macromolecules are broken down into smaller, absorbable molecules (1).
- These smaller molecules are absorbed for nutrition (1).