3.1.4.2 Many proteins are enzymes - AQA A Level Biology Summary Notes
The effects of the following factors on the rate of enzyme controlled reactions – enzyme
concentration, substrate concentration, concentration of competitive and non competitive
inhibitors, pH and temperature
Student could be given the hydrogen ion concentration of a solution in order to calculate its pH,
using the formula
1) Temperature
Initially, increasing temperature will increase rate of reaction because enzyme and substrate will
have more thermal energy, so more kinetic energy, so more frequent enzyme-substrate collisions, so
more ESCs formed
BUT
If temperature is too high then the rate of reaction will fall because the enzyme will denature
The increased kinetic energy causes hydrogen bonds within the enzymes tertiary structure to break,
causing the active site to lose shape. The substrate is no longer complementary to the active site, so
the substrate no longer binds to the active site, so ESCs are not formed
Notes:
- Different enzymes have different optimum temperatures, so it is not always 37 degrees
- An enzyme can still be functioning very slowly once denatured before finally stopping
- Desaturation is IRREVERSIBLE
- Must describe every step of reasoning – substrate being complementary to active site and
binding to active site are two SEPERATE POINTS
2) pH
Measures the acidity/basicity of a solution – it is a measure of the hydrogen ion (H+)
concentration
Ranges from pH1 to pH14 – lower pH values mean higher H+ concentrations (acidic)
Acidic solutions have pH below 7, Basic/Alkali solutions have pH above 7
Deionised water is pH7, which is termed “neutral”
The effects of the following factors on the rate of enzyme controlled reactions – enzyme
concentration, substrate concentration, concentration of competitive and non competitive
inhibitors, pH and temperature
Student could be given the hydrogen ion concentration of a solution in order to calculate its pH,
using the formula
1) Temperature
Initially, increasing temperature will increase rate of reaction because enzyme and substrate will
have more thermal energy, so more kinetic energy, so more frequent enzyme-substrate collisions, so
more ESCs formed
BUT
If temperature is too high then the rate of reaction will fall because the enzyme will denature
The increased kinetic energy causes hydrogen bonds within the enzymes tertiary structure to break,
causing the active site to lose shape. The substrate is no longer complementary to the active site, so
the substrate no longer binds to the active site, so ESCs are not formed
Notes:
- Different enzymes have different optimum temperatures, so it is not always 37 degrees
- An enzyme can still be functioning very slowly once denatured before finally stopping
- Desaturation is IRREVERSIBLE
- Must describe every step of reasoning – substrate being complementary to active site and
binding to active site are two SEPERATE POINTS
2) pH
Measures the acidity/basicity of a solution – it is a measure of the hydrogen ion (H+)
concentration
Ranges from pH1 to pH14 – lower pH values mean higher H+ concentrations (acidic)
Acidic solutions have pH below 7, Basic/Alkali solutions have pH above 7
Deionised water is pH7, which is termed “neutral”
