5.2 Effects of Temperature & pH (Cambridge (CIE) O Level Biology): Flashcards
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Give two ways to follow the progress of an enzyme-catalysed reaction.
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Give two ways to follow the progress of an enzyme-catalysed reaction.
Measure the rate of product formation
Measure the rate of substrate disappearance
How can you measure the rate of the catalase reaction?
Catalase breaks down hydrogen peroxide, releasing oxygen gas; collect and measure the volume of oxygen using a gas syringe or measuring cylinder.
Define catalase.
An enzyme that breaks down hydrogen peroxide into water and oxygen.
In the amylase-starch experiment, how do you know all the starch has been broken down?
The iodine stops turning blue-black (stays orange-brown), showing that no starch remains.
Amylase breaks down starch, so the blue-black iodine result disappears once all the has been digested.
Amylase breaks down starch, so the blue-black iodine result disappears once all the starch has been digested.
In the amylase temperature experiment, what does a shorter reaction time tell you?
The faster the iodine stops turning blue-black, the faster the enzyme is working at that temperature.
Why is a buffer solution added in the pH investigation of amylase?
To keep the mixture at a constant, known pH while the reaction is investigated.
In the pH investigation of amylase, the end point is reached when the iodine remains .
In the pH investigation of amylase, the end point is reached when the iodine remains orange-brown.
How is amylase activity compared at different pH values?
The less time taken for the iodine to stay orange-brown, the better the enzyme works at that pH.
True or False?
In the amylase experiment, iodine turning blue-black means starch is still present.
True.
Iodine stays blue-black while starch remains, and turns orange-brown once the starch is broken down.
Define the optimum temperature.
The temperature at which an enzyme works fastest — about 37 °C in the human body.
Define denatured.
When an enzyme's active site loses its shape (due to high temperature or extreme pH) so the substrate no longer fits and activity stops.
Why does enzyme activity increase as temperature rises towards the optimum?
Molecules gain more kinetic energy and move faster, so there are more collisions between enzyme and substrate.
Why does enzyme activity fall above the optimum temperature?
High temperatures break the bonds holding the enzyme's shape, distorting the active site until the enzyme is denatured.
Once an enzyme has been denatured by heat, the change is largely .
Once an enzyme has been denatured by heat, the change is largely irreversible.
What is the optimum pH for most enzymes, and give an exception.
Most work best at pH 7; stomach enzymes work best at about pH 2, and duodenum enzymes at about pH 8–9.
True or False?
Low temperatures denature enzymes.
False.
Low temperatures do not denature enzymes; they simply slow activity because there is less kinetic energy and fewer collisions.
How does a pH that is too high or too low affect an enzyme?
It breaks the bonds holding the protein's shape, changing the active site so the substrate no longer fits — the enzyme may become denatured.
Enzymes in the human body have an optimum temperature of about .
Enzymes in the human body have an optimum temperature of about 37 °C.
Why can a denatured enzyme no longer catalyse its reaction?
The shape of its active site is lost, so the substrate can no longer bind to it.
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