Factors that Affect Enzyme Action (Cambridge (CIE) AS 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.
Define V~max~.
The maximum rate of an enzyme-catalysed reaction, reached when the enzyme is saturated with substrate.
Define the Michaelis-Menten constant (K~m~).
The substrate concentration at which an enzyme works at half of its V~max~ (½Vmax).
What does K~m~ tell us about an enzyme?
It measures the enzyme's affinity for its substrate.
Does a low K~m~ mean a high or low affinity for the substrate?
A high affinity — only a low substrate concentration is needed to reach ½Vmax.
How is K~m~ found from a graph of rate against substrate concentration?
Read off V~max~, then find the substrate concentration that gives ½V~max~.
Km is the substrate concentration that gives of the maximum rate.
Km is the substrate concentration that gives half of the maximum rate.
True or False?
An enzyme with a high Km has a high affinity for its substrate.
False.
A high K~m~ means a low affinity for the substrate.
Define competitive inhibitor.
A molecule with a shape similar to the substrate that binds to the active site, blocking the substrate.
Define non-competitive inhibitor.
A molecule that binds to the enzyme at a site other than the active site, changing the shape of the active site.
How does a competitive inhibitor reduce enzyme activity?
It binds to the active site, preventing the substrate from binding and forming enzyme-substrate complexes.
How does a non-competitive inhibitor reduce enzyme activity?
It binds away from the active site, changing the active site's shape so the substrate can no longer bind.
Define reversible inhibitor.
An inhibitor that binds temporarily and can detach from the enzyme, so its effect is not permanent.
How can the effect of a competitive inhibitor be overcome?
By increasing the substrate concentration, so substrate out-competes the inhibitor for the active sites.
A inhibitor binds to a site other than the active site.
A non-competitive inhibitor binds to a site other than the active site.
True or False?
A competitive inhibitor binds to the active site of an enzyme.
True.
Its shape is similar to the substrate, so it competes for the active site.
Define immobilised enzyme.
An enzyme that is trapped or attached to an inert support (e.g. in alginate beads) rather than being free in solution.
How can enzymes be immobilised in a practical investigation?
By trapping them inside alginate beads.
How does the activity of an immobilised enzyme usually compare with the same enzyme free in solution?
Immobilised enzymes usually have a slightly lower activity, because the substrate must diffuse to the active sites, which are less accessible.
State two advantages of using immobilised enzymes.
They can be easily recovered and reused.
The product is not contaminated with enzyme.
Give one advantage of immobilised enzymes relating to stability.
They are more stable and less easily denatured by changes in temperature and pH.
Enzymes are commonly immobilised by trapping them in beads.
Enzymes are commonly immobilised by trapping them in alginate beads.
True or False?
Immobilised enzymes are difficult to reuse.
False.
A key advantage is that they can be easily recovered and reused.
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