1. 20.3 Factors Affecting Enzyme Activity
The activity of an enzyme describes how fast an enzyme catalyzes the reaction and is strongly affected by reaction conditions, such as
temperature.
pH.
concentration of the enzyme and substrate.
Learning Goal Describe the effect of changes of temperature, pH, concentration of enzyme, and concentration of substrate on enzyme activity.
Thermophiles survive in the high
temperatures (50°C to 120°C) of
a hot spring.

2. Temperature and Enzyme Activity
Enzymes
are most active at an optimum temperature (usually 37°C in humans).
show little activity at low temperatures.
lose activity at high temperatures as denaturation occurs.
Core Chemistry Skill Identifying Factors Affecting Enzyme
Activity

3. Temperature and Enzyme Activity
Thermophiles
live in environments where temperatures range from 50°C to 120°C.
have enzymes with tertiary structures that are not destroyed by such high temperatures.

4. pH and Enzyme Activity Enzymes
are most active at optimum pH, where proper tertiary structure of the protein is maintained.
contain R groups of amino acids with proper charges at optimum pH.
lose activity in low or high pH as tertiary structure is disrupted.

5. Optimum pH Values Enzymes in the body have an optimum pH of about 7.4.
certain organs operate at lower or higher optimum pH values.

6. Enzyme Concentration An increase in enzyme concentration
increases the rate of reaction (at constant substrate concentration).
binds more substrate with enzyme.

7. Substrate Concentration
An increase in substrate
concentration
increases the rate of reaction (at constant enzyme concentration).
eventually saturates an enzyme with substrate to give maximum activity.

8. Study Check
Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction: A. increasing the concentration of sucrase B. changing the pH to 4.0 C. running the reaction at 70°C 1) no change 2) increase 3) decrease

9. Solution
Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction: A. increasing the concentration of sucrase 2) increase B. changing the pH to 4.0 3) decrease C. running the reaction at 70°C 3) decrease 1) no change 2) increase 3) decrease