03.04 Enzyme Action: Temperature

Question 1

Explain how temperature affects the rate of enzyme activity at low and increasing temperatures. (5 marks)

Mark Scheme:

1. At low temperatures, enzyme activity is slow because molecules have low kinetic energy. (1 mark)
2. This results in fewer collisions between enzyme and substrate molecules. (1 mark)
3. As temperature increases, kinetic energy rises, leading to more frequent and energetic collisions. (1 mark)
4. This increases the likelihood of substrate binding to the enzyme’s active site, raising the reaction rate. (1 mark)
5. Bonds within the substrate and enzyme are more likely to break or form, facilitating the reaction. (1 mark)

Question 2

Describe what happens to enzyme activity beyond its optimum temperature. (6 marks)

Mark Scheme:

1. Beyond the optimum temperature, excessive vibration occurs within the enzyme molecules. (1 mark)
2. This breaks hydrogen bonds and other weak bonds that maintain the enzyme’s 3D structure. (1 mark)
3. The enzyme’s active site deforms, reducing its ability to bind the substrate. (1 mark)
4. As a result, enzyme activity decreases, and the reaction rate declines. (1 mark)
5. At very high temperatures, the enzyme becomes completely denatured and unable to function. (1 mark)
6. The reaction rate eventually drops to zero. (1 mark)

Question 3

Draw and annotate a graph showing the effect of temperature on enzyme activity, including the regions of low activity, optimum activity, and denaturation. (5 marks)

Mark Scheme:

1. Correctly shaped curve: Slow rise at low temperatures, peak at optimum, and steep decline after. (1 mark)
2. Label X-axis: Temperature, Y-axis: Rate of Reaction. (1 mark)
3. Annotate low-temperature region: Low kinetic energy, few collisions. (1 mark)
4. Annotate peak: Optimum temperature, maximum enzyme activity. (1 mark)
5. Annotate high-temperature region: Denaturation, loss of enzyme structure and activity. (1 mark)

Question 4

Why do thermophilic bacteria have enzymes with high optimum temperatures, and how is this applied in industry? (4 marks)

Mark Scheme:

1. Thermophilic bacteria live in extreme environments, such as hot springs, so their enzymes are adapted to function at high temperatures. (1 mark)
2. These enzymes have stronger bonds (e.g., disulfide bridges) that resist denaturation. (1 mark)
3. Industrial application: Thermophilic enzymes are used in products like biological washing powders, which operate at high temperatures to remove stains. (1 mark)
4. High-temperature stability makes these enzymes more efficient and durable in industrial processes. (1 mark)

Question 5

Explain the importance of the optimum temperature for enzyme activity in humans. (5 marks)

Mark Scheme:

1. The optimum temperature for most human enzymes is around 40°C, close to body temperature (37°C). (1 mark)
2. This ensures enzymes can work efficiently in physiological conditions. (1 mark)
3. At this temperature, the enzyme’s active site is perfectly suited for substrate binding. (1 mark)
4. Deviations from the optimum temperature reduce enzyme activity, impacting metabolic processes. (1 mark)
5. Extreme temperatures, especially high, can lead to denaturation and enzyme inactivation. (1 mark)

Question 6

Compare the effects of low and high temperatures on enzyme activity. (5 marks)

Mark Scheme:

1. At low temperatures, molecules have low kinetic energy, resulting in fewer enzyme-substrate collisions. (1 mark)
2. Reaction rates are slow due to reduced interaction between enzyme and substrate. (1 mark)
3. High temperatures increase kinetic energy, initially raising the reaction rate. (1 mark)
4. Beyond the optimum, high temperatures cause denaturation, deforming the active site and reducing activity. (1 mark)
5. Ultimately, high temperatures can stop the reaction entirely, unlike low temperatures where activity is slow but not halted. (1 mark)

Question 7

Describe how the fraction of folded and functional enzymes changes with temperature and its effect on reaction rate. (4 marks)

Mark Scheme:

1. At low temperatures, most enzymes remain folded but function slowly due to low kinetic energy. (1 mark)
2. At optimum temperature, enzymes are fully folded and functional, maximizing reaction rate. (1 mark)
3. Beyond the optimum, the fraction of folded enzymes decreases as denaturation begins. (1 mark)
4. This reduces the number of active enzymes, causing the reaction rate to decline. (1 mark)

Question 8

How does the temperature vs. reaction rate curve for enzymes reflect changes in kinetic energy and enzyme structure? (6 marks)

Mark Scheme:

1. At low temperatures, the curve rises gradually as kinetic energy increases and collisions become more frequent. (1 mark)
2. The steep rise to the peak reflects the enzyme’s optimum temperature, where activity is highest. (1 mark)
3. The peak corresponds to the maximum number of successful enzyme-substrate collisions. (1 mark)
4. After the optimum, the curve falls sharply due to denaturation. (1 mark)
5. Loss of enzyme structure leads to a rapid decline in activity. (1 mark)
6. The graph illustrates the balance between kinetic energy and structural stability of enzymes. (1 mark)

Question 9

Explain how enzymes adapted to different environments exhibit variations in their optimum temperatures. (5 marks)

Mark Scheme:

1. Enzymes from thermophilic organisms have higher optimum temperatures to function in hot environments. (1 mark)
2. These enzymes have stronger bonds (e.g., disulfide bonds) that prevent denaturation. (1 mark)
3. Enzymes from mesophilic organisms, like humans, have optima near 40°C, suited to moderate environments. (1 mark)
4. Enzymes from psychrophilic organisms (cold environments) function well at low temperatures, with flexible structures. (1 mark)
5. This adaptation ensures enzymes are efficient in the organism’s natural habitat. (1 mark)

Question 10

Outline the consequences of enzyme denaturation due to high temperature. (4 marks)

Mark Scheme:

• Denaturation causes the enzyme’s active site to lose its specific shape. (1 mark)
• Substrates can no longer bind effectively, reducing reaction rates. (1 mark)
• At extreme temperatures, enzymes become completely non-functional, and reactions stop. (1 mark)
• This is irreversible, as the enzyme cannot regain its original structure. (1 mark)