factors affecting enzyme activity

Question 1

Describe how temperature affects enzyme activity (3)

Answer 1

1. Initially, as temperature increases, kinetic energy increases, molecules move faster, and the rate of enzyme-substrate collisions increases, speeding up the reaction;
2. At optimum temperature, the rate of reaction is at its maximum;
3. Beyond the optimum temperature, bonds in the enzyme’s tertiary structure break, the active site changes shape, and the enzyme becomes denatured

Question 2

What is the temperature coefficient (e.g. Q10)? (2)

Answer 2

Q10 shows how much the rate of reaction changes when the temperature is raised by 10°C;

Q10 = 2 means the rate doubles with a 10°C increase, and Q10 = 3 means the rate trebles

Question 3

What happens to an enzyme when it denatures due to temperature? (3)

Answer 3

The enzyme’s active site changes shape;

The substrate is no longer complementary;

So enzyme-substrate complexes can no longer form

Question 4

Describe how pH affects enzyme activity (4)

Answer 4

Enzymes have an optimum pH.;

pH changes break hydrogen and ionic bonds in the enzyme’s tertiary structure;

Altering the active site’s shape;

The substrate is no longer complementary, and the enzyme is denatured

Question 5

How does enzyme concentration affect the rate of reaction? (2)

Answer 5

1. Increasing enzyme concentration increases the chance of successful collisions and the formation of enzyme-substrate (ES) complexes, increasing the reaction rate;
2. If the substrate is limited, the reaction rate will eventually plateau, and adding more enzyme will have no effect

Question 6

How does substrate concentration affect the rate of reaction? (3)

Answer 6

1. Increasing substrate concentration increases the chance of successful collisions, increasing the formation of ES complexes and the reaction rate;
2. At saturation point, all active sites are occupied, and the reaction rate reaches a maximum;
3. Substrate concentration decreases over time unless more is added, so the reaction rate decreases over time

Question 7

How can you measure the rate of an enzyme-controlled reaction? (2)

Answer 7

1. Measure how fast the product appears (e.g., oxygen production by catalase breaking down hydrogen peroxide);
2. Measure how fast the substrate disappears (e.g., using the iodine starch test to time starch breakdown by amylase)

Question 8

How can you investigate the effect of temperature on catalase activity? (7)

Answer 8

1. Set up tubes containing the same volume and concentration of hydrogen peroxide and buffer solution;
2. Place tubes in water baths at different temperatures (e.g., 10-40°C);
3. Leave the tubes for 5 minutes to reach the set temperature;
4. Add the same volume and concentration of catalase to each tube;
5. Measure oxygen production in 60 seconds using a stopwatch;
6. Repeat 3 times and calculate the mean volume of oxygen produced;
7. Calculate the mean rate of reaction (cm³/second)

Question 9

What is the role of a negative control in the experiment of investigating temperature on catalase activity? (1)

Answer 9

Shows that the enzyme alone is not producing oxygen

Question 10

How can you investigate the effect of pH on enzyme activity? (1)

Answer 10

Use buffer solutions with different pH levels for each tube

Question 11

How can you investigate the effect of substrate concentration? (1)

Answer 11

Use different concentrations of hydrogen peroxide, made by serial dilutions

Question 12

How can you investigate the effect of enzyme concentration? (1)

Answer 12

Use different concentrations of catalase in each tube

Question 13

What is the key principle for controlling variables in enzyme experiments? (1)

Answer 13

Only one variable should be changed at a time in the experiment