4.2 Factors Affecting Enzyme Activity Flashcards
What factors affect enzyme activity?
Temperature
pH
Substrate and enzyme concentration
How does temperature affect enzyme activity?
As the temperature increases up to optimum temperature, so does the rate of reaction
Why does increasing temperature up until optimum temperature increase the rate of reaction?
- 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
What is the temperature coefficient
, Q10, of a reaction?
A measure of how much the rate of reaction increases with a 10°C rise in temperature
What happens to an enzyme in an environment where the temperature is above optimum?
The enzyme denatures
Why do enzymes denature above optimum temperature?
- 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
Why does an enzyme changing shape mean that it has denatured?
- 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
What is optimum temperature?
The temperature at which an enzyme has the highest rate of activity
At what point does the temperature coefficient no longer matter in an enzyme-controlled reaction?
When the enzymes denature
When is the decrease in enzyme activity less rapid? Before or after optimum temperature?
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
Which enzymes are more susceptible to temperature change - those adapted to hot temperatures or the adapted to cold temperatures?
Those adapted to cold
- because they are more flexible
- and therefore less stable
What are thermophiles?
Organisms adapted to hot environments
Why are enzymes adapted to hot environments more stable than other enzymes?
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
What is optimum pH?
The pH at which an enzyme works best
The specific hydrogen ion concentration at which an enzyme works best
What is a change in pH?
A change in hydrogen ion concentration
What happens when the pH changes from optimum pH?
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
What is renaturation?
When an protein resumes it’s normal shape once the environment has been returned to optimum pH
Do proteins always return to their original structure when the pH is returned to optimum pH?
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
Why does pH affect enzyme activity?
-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)
