Enzymes Flashcards
What is an enzyme?
A biological catalyst, that speeds up the rate of reaction by lowering the activation energy needed for the reaction to occur and without being used up.
Explain the lock and key model?
The shape of the active site is exactly complementary to the specific substrate and the substrate fits in exactly as it binds to the active site forming an enzyme-substrate complex. The enzyme substrate complex places stress on the bonds causing them to form or break, leading to the reaction and products being formed. The products are released and the enzyme is unchanged.
Explain the induced fit model?
Before the reaction the shape of the substrate is not complementary to the active site. The substrate binds to the active site causing the shape of the active site to change so it becomes complementary to the substrate. An enzyme-substrate complex then forms causing the bonds to form or break due to the bonds being stressed, leading to the reaction and products being formed. The products are released and the enzyme returns to its original position.
What are the similarities between the lock and key and induced fit model?
In both the substrate binds to the active site and an enzyme-substrate complex is formed.
What are the differences between the lock and key and induced fit model?
In the induced fit model the active site isn’t complementary at the start, but in the lock and key model the active site is complementary.
The active site changes shape when the substrate binds in the induced fit model but does not in the lock and key model.
How do enzymes speed up the rate of reaction?
All reactions require a certain amount of energy before they will occur. Enzyme work by lowering the activation energy needed. This makes the reaction occur faster and also allows the reaction to occur at lower temperatures.
How do enzymes lower the activation energy?
By forming an enzyme-substate complex. When the substrate binds to the active site, the active site changes to become a complementary shape to the substate to form an enzyme-substate complex. This stresses the bonds in the substrate allowing them to break or form more easily meaning less energy is needed.
How does increasing the temperature up to the enzymes optimum effect the enzymes activity?
The enzymes and substrates have more kinetic energy, so move faster, so an increased frequency of successful collisions, so an increase in enzyme-substrate complexes forming, so an increased rate of reaction.
How does carrying out the reaction at the enzymes optimum temperature effect the rate of reaction?
The maximum number of successful collisions occurring, so the maximum number of enzyme-substrate complexes forming.
How does increasing the temperature past the enzymes optimum effect enzyme activity?
The enzymes gain even more kinetic energy, causing the hydrogen bonds that hold the tertiary structure together to break, this changes the tertiary structure, which causes changes in the active site. At first the substrate fits less easily into the active site so fewer enzyme-substrate complexes form so the rate of reaction decreases. At even higher temperatures the enzymes denature because so many hydrogen bonds are broken, the active site is not complementary shaped, so no enzyme-substrate complexes form and the rate of reactions decreases further.
How does carrying out the reaction at the enzymes optimum pH effect the rate of reaction?
The maximum number of successful collisions so the maximum number of enzyme-substrate complexes form because the active site is most complementary to the substrate.
How does increasing the pH above or below the optimum effect the enzyme activity?
Below the optimum H+ increases and above the optimum H+ decreases. H+ ions are attracted to amino acids that form the active site which alters their charge. This causes the hydrogen and ionic bonds holding the tertiary structure together to break , so the tertiary structure changes, so the active site changes shape, so it is no longer complementary to the substrate, so it can’t bind, which means less or no enzyme-substrate complexes form and the rate of reaction decreases.
Explain the rate of reaction at low enzyme concentrations?
When there is an excess of substrate the enzyme concentration limits the rate of reaction. There are not enough active sites available for all the substrates to bind to at one time so less enzyme-substrate complexes form at one time. The enzymes active sites are saturated.
Explain the rate of reaction as you increase the enzyme concentration?
Increasing the enzyme concentration means there are more active sites available for substrates to bind to. This means more enzyme-substrate complexes form at one time.
Explain the rate of reaction as you increase the enzyme concentration further?
Enzyme concentration is no longer the limiting factor and substrate concentration is. There are now empty active sites as there is not enough substrate available to bind to all active sites at one time.