Factors that Affect Enzyme Action (Cambridge (CIE) A Level Biology): Flashcards
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How does increasing temperature affect enzyme activity up to the optimum?
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How does increasing temperature affect enzyme activity up to the optimum?
Kinetic energy increases, so there are more frequent successful collisions between enzyme and substrate, giving a faster rate.
Define optimum temperature.
The temperature at which an enzyme works at its fastest rate.
What happens to an enzyme above its optimum temperature?
It begins to denature — the active site changes shape and is no longer complementary to the substrate.
Define denaturation.
The change in shape of an enzyme's active site (from the breaking of bonds) so that the substrate can no longer bind.
Why does enzyme activity fall to zero at high temperatures?
The active site is permanently denatured, so no enzyme-substrate complexes can form.
Above the optimum temperature, enzymes begin to .
Above the optimum temperature, enzymes begin to denature.
True or False?
A denatured enzyme can return to its normal shape when cooled.
False.
Denaturation is permanent — the active site does not return to its original shape.
Define optimum pH.
The pH at which an enzyme works at its fastest rate.
What happens to an enzyme at a pH far from its optimum?
It denatures — the active site changes shape, so the substrate can no longer bind.
Why do changes in pH affect the shape of an enzyme?
A change in H^+^ ion concentration breaks hydrogen and ionic bonds, altering the shape of the active site.
Why are buffer solutions used when investigating the effect of pH?
To keep the pH constant at each set value throughout the experiment.
A solution is used to keep pH constant during an experiment.
A buffer solution is used to keep pH constant during an experiment.
True or False?
All enzymes have the same optimum pH.
False.
Different enzymes have different optimum pH values.
How does increasing enzyme concentration affect the rate of reaction when substrate is in excess?
More active sites are available, so more enzyme-substrate complexes form, giving a faster rate.
Why does the rate plateau at high enzyme concentrations?
Substrate becomes the limiting factor — there is not enough substrate to occupy all the active sites.
If substrate is in excess, increasing enzyme concentration the rate of reaction.
If substrate is in excess, increasing enzyme concentration increases the rate of reaction.
Define limiting factor.
A factor that, when in short supply, restricts the rate of a reaction.
At high enzyme concentration, what becomes the limiting factor?
Substrate concentration.
True or False?
Increasing enzyme concentration increases the rate indefinitely.
False.
Once substrate is limiting, adding more enzyme has no further effect on the rate.
How does increasing substrate concentration affect the rate of reaction?
More enzyme-substrate complexes form, giving a faster rate, until all active sites are occupied.
Why does the rate plateau at high substrate concentrations?
All active sites are occupied (saturated), so enzyme concentration becomes the limiting factor.
The rate plateaus when all enzyme sites are occupied.
The rate plateaus when all enzyme active sites are occupied.
Define enzyme saturation.
When all active sites are occupied by substrate, so the rate cannot increase any further.
At high substrate concentration, what is the limiting factor?
Enzyme concentration (the number of available active sites).
True or False?
At low substrate concentration, substrate is the limiting factor.
True.
With few substrate molecules, many active sites are empty, so adding more substrate increases the rate.
Define enzyme inhibitor.
A substance that reduces or stops the rate of an enzyme-catalysed reaction.
How does increasing inhibitor concentration affect the rate of reaction?
The rate decreases, because more enzyme molecules are inhibited at any one time.
Increasing inhibitor concentration the rate of an enzyme-catalysed reaction.
Increasing inhibitor concentration decreases the rate of an enzyme-catalysed reaction.
For a competitive inhibitor, how does increasing substrate concentration affect the amount of inhibition?
It reduces inhibition, because substrate out-competes the inhibitor for the active sites.
For a non-competitive inhibitor, how does increasing substrate concentration affect the amount of inhibition?
It has no effect, because the inhibitor does not bind at the active site.
True or False?
Increasing substrate concentration can reduce the effect of a non-competitive inhibitor.
False.
It only reduces the effect of a competitive inhibitor.
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