Limiting Factors Affecting Enzymes: Temperature

Question 1

Enzymes have a specific optimum temperature – the

Answer 1

temperature at which they catalyse a reaction at the maximum rate

Question 2

Lower temperatures either Lower temperatures either prevent reactions from proceeding or slow them down

this is done as

Answer 2

Molecules move relatively slow

Lower frequency of successful collisions between substrate molecules and active site of enzyme

Less frequent enzyme-substrate complex formation

Substrate and enzyme collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)

Question 3

Higher temperatures speed up reactions why is this

Answer 3

Molecules move more quickly

Higher frequency successful collisions between substrate molecules and active site of enzyme

More frequent enzyme-substrate complex formation

Substrate and enzyme collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)

Question 4

However, as temperatures continue to increase, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature:

what happens

Answer 4

Bonds (eg. hydrogen bonds and ionic) holding the enzyme molecule in its precise shape start to break

This causes the tertiary structure of the protein (ie. the enzyme) to change

This permanently damages the active site, preventing the substrate from binding

Denaturation has occurred if the substrate can no longer bind not anymore complementary

Question 5

Very few human enzymes can function at temperatures above 50°C
This is because

Answer 5

humans maintain a body temperature of about 37°C, therefore even temperatures exceeding 40°C will cause the denaturation of enzymes

High temperatures causes the hydrogen and ionic bonds between amino acids to break, changing the conformation of the enzyme

Question 6

Exam Tip

When answering questions about reaction rates for enzyme-catalysed reactions, make sure to explain how the temperature affects the speed at
which the molecules (enzymes and substrates) are moving and how this, in turn, affects the number of successful collisions.