4.2 Factors Affecting Enzyme Activity

Question 1

How does temperature affect enzyme activity?

Answer 1

• the increase in temperature, increases the kinetic energy of the particles therefore increasing collisions between substrate and enzyme. This leads to an increase in the rate of reaction

Question 2

What is the temperature coefficient, Q10, of a reaction?

Answer 2

A measure of how much the rate of reaction increases with a 10°C rise in temperature

usually in enzyme controlled reactions the rate of reaction doubles with a 10°C temperature increase

Question 3

Describe denaturation from temperature

Answer 3

At high temperatures the bonds holding the protein together vibrate and beak. This results in a change in the precise tertiary structure. The enzyme has changed shape and has therefore denatured

When an enzyme is denatured the active site changes shape and is no longer complementary to the substrate. The substrate can no longer fit into the active site and the enzyme no longer functions as a catalyst

Question 4

What is the optimum temperature?

Answer 4

The temperature at which the enzyme has the highest rate of activity.
Once the enzymes have denatured above the optimum temperature, the decrease in rate of reaction is rapid. At this point the temperature coefficient does not apply anymore as the enzymes have denatured

Question 5

How does pH affect enzyme activity?

Answer 5

• a change in pH changes refers to a change in hydrogen ion concentration. Hydrogen ions interact with polar and charged R-groups
• the more hydrogen ions present, the less the R-groups are able to interact with each other, this leads to bond breaking and the shape of the enzyme changing
• the active site will only be in right shape at a certain hydrogen ion concentration (optimum pH)
• when the ph changes, the structure of the enzymes is irreversibly altered and the active site will no longe be complementary to the substrate so has now denatured. This reduces rate of reaction

Question 6

How does substrate and enzyme concentration affect enzyme activity?

Answer 6

When the concentration of substrate is increases, the number of substrate molecules increases which leads to higher collision rate and more enzyme-substrate complexes form.
The rate of reaction therefore increases

When the concentration of enzymes increases, the number of available active sites in a particular volume increases. Rate of reaction increases

V max is the maximum of rate of reaction when all active sites are occupied by substrate particles. The only way to increase V max is to add more enzymes or increase temperature