4.2 Factors Affecting Enzyme Activity

Question 1

What factors affect enzyme activity?

Answer 1

Temperature
pH
Substrate and enzyme concentration

Question 2

How does temperature affect enzyme activity?

Answer 2

As the temperature increases up to optimum temperature, so does the rate of reaction

Question 3

Why does increasing temperature up until optimum temperature increase the rate of reaction?

Answer 3

• increasing the temperature of a reaction environment increases the kinetic energy of the particles
• which causes faster movement of particles
• resulting in more frequent collisions
• more successful collisions between substrate and enzyme = increase in rate of reaction

Question 4

What is the temperature coefficient

, Q10, of a reaction?

Answer 4

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

Question 5

What happens to an enzyme in an environment where the temperature is above optimum?

Answer 5

The enzyme denatures

Question 6

Why do enzymes denature above optimum temperature?

Answer 6

• At higher temperatures the bonds holding the protein together vibrate more
• as temp. increases the vibrations increase until bonds strain and then break
• the breaking of these bonds results in a change in the precise tertiary structure of the protein
• the enzyme has changed shape and has therefore denatured
  (The temp only needs to change slightly for the enzyme to denature

Question 7

Why does an enzyme changing shape mean that it has denatured?

Answer 7

• the active site changes shape and is no longer complementary to the substrate
• the substrate can no longer bind to the enzyme because it no longer fits into the active site

Question 8

What is optimum temperature?

Answer 8

The temperature at which an enzyme has the highest rate of activity

Question 9

At what point does the temperature coefficient no longer matter in an enzyme-controlled reaction?

Answer 9

When the enzymes denature

Question 10

When is the decrease in enzyme activity less rapid? Before or after optimum temperature?

Answer 10

Before - because the enzymes have not denatured, they are just less rapid

The decrease in rate of reaction is more rapid after optimum temperature because the enzymes have denatured and are no longer the correct shape to bind to the substrate. It is rapid because the enzymes denature around the same time

Question 11

Which enzymes are more susceptible to temperature change - those adapted to hot temperatures or the adapted to cold temperatures?

Answer 11

Those adapted to cold

• because they are more flexible
• and therefore less stable

Question 12

What are thermophiles?

Answer 12

Organisms adapted to hot environments

Question 13

Why are enzymes adapted to hot environments more stable than other enzymes?

Answer 13

Because they have an increased number of bonds in their tertiary structures
(Particularly hydrogen bonds and surface bonds)
- the shapes of these enzymes and their active sites, are more resistant to change as temperature rises

Question 14

What is optimum pH?

Answer 14

The pH at which an enzyme works best

The specific hydrogen ion concentration at which an enzyme works best

Question 15

What is a change in pH?

Answer 15

A change in hydrogen ion concentration

Question 16

What happens when the pH changes from optimum pH?

Answer 16

The structure if the enzyme, and therefore the active site, is altered.
However of the pH returns to the optimum again then the protein will resume its normal shape and catalyse the reaction again

Question 17

What is renaturation?

Answer 17

When an protein resumes it’s normal shape once the environment has been returned to optimum pH

Question 18

Do proteins always return to their original structure when the pH is returned to optimum pH?

Answer 18

No - when the pH changes more significantly (beyond a certain pH)

• the structure of the enzyme is irreversibly altered
• and the active site will no longer be complementary to the substrate
• the enzyme has denatured

Question 19

Why does pH affect enzyme activity?

Answer 19

-hydrogen ions interact with polar and charged R-groups.
-Changing the concentration of hydrogen ions therefore changes the degree of this interaction
- the interaction of R-groups with hydrogen ions also affects the interaction of R-groups with each other
More hydrogen ions = less R-groups interactions w/ each other= binds breaking = shape of enzyme changing (reverse is true for less hydrogen ions)