Topic 3: Enzymes Flashcards
State the role of enzymes as globular proteins in cells. [1 Mark]
Enzymes catalyse intracellular (e.g., mitochondria) or extracellular (e.g., gut) reactions. (1 mark)
Definitions I:
(a) Enzyme
(b) Active site
(c) Substrate
(a) Enzyme: Globular protein catalysing reactions.
(b) Active site: Region binding substrate specifically.
(c) Substrate: Molecule acted on by enzyme.
In a lab, outline how to measure the rate of H₂O₂ breakdown by catalase. [2 Marks]
Mix H₂O₂ with catalase, measure O₂ volume over time (1 mark); Rate = O₂ produced/time (1 mark). (2 marks)
In a liver cell, explain the mode of action of catalase using the lock-and-key hypothesis. [2 Marks]
Catalase’s active site fits H₂O₂ (lock-and-key) (1 mark); Lowers activation energy, breaks to H₂O + O₂ (1 mark). (2 marks)
In saliva, explain how amylase works using the induced-fit hypothesis. [2 Marks]
Amylase’s active site adjusts to starch (induced-fit) (1 mark); Lowers energy, hydrolyses to maltose (1 mark). (2 marks)
Explain how pH, using buffers, impacts pepsin activity in the stomach. [3 Marks]
Test pepsin with protein, buffers (pH 2-7) (1 mark); Optimal at pH 2, active site fits (1 mark); Denatures at high pH (1 mark). (3 marks)
In a yeast experiment, outline how enzyme concentration alters fermentation rate. [2 Marks]
Increase yeast enzyme, measure CO₂ in fermentation (1 mark); Rate rises, then plateaus as substrate limits (1 mark). (2 marks)
Using a colorimeter, describe how to track starch digestion by amylase. [2 Marks]
Mix starch, amylase, iodine; colorimeter tracks blue-black fading (1 mark); Rate = absorbance decrease/time (1 mark). (2 marks)
Investigate how temperature affects catalase activity in a potato extract. [3 Marks]
Vary temp (20-60°C), measure O₂ from H₂O₂ (1 mark); Rate peaks at optimum ~40°C (1 mark); Denatures above (1 mark). (3 marks)
Describe how substrate concentration affects lactase in milk digestion. [2 Marks]
Vary lactose, measure glucose production (1 mark); Rate increases, then levels at saturation (1 mark). (2 marks)
Explain Vmax and Km in comparing enzyme affinity for substrates. [3 Marks]
Vmax: Max reaction rate at saturation (1 mark); Km: Substrate conc. at ½ Vmax (1 mark); Lower Km = higher affinity (1 mark). (3 marks)
Describe how a non-competitive inhibitor alters protease activity in digestion. [2 Marks]
Non-competitive binds elsewhere, alters shape (1 mark); Lowers rate, not reversed by substrate (1 mark). (2 marks)
In a drug study, explain how a competitive inhibitor affects enzyme activity. [2 Marks]
Competitor binds active site, e.g., drug vs. substrate (1 mark); Reduces rate, reversible by excess substrate (1 mark). (2 marks)
Investigate the activity of immobilised lactase in alginate vs. free solution. [3 Marks]
Immobilise lactase in alginate, test milk (1 mark); Free lactase faster, immobilised reusable (1 mark); Advantage: stability, cost-effective (1 mark). (3 marks)
Analyse the effects of temperature and inhibitor concentration on amylase activity. [4 Marks]
Temp increases rate to optimum, then denatures (1 mark); Inhibitor binds, slows rate (1 mark); Competitive reversible (1 mark); Non-competitive persistent (1 mark). (4 marks)
