Enzymes Flashcards
What is an enzyme
A protein that acts as a biological catalyst as it speeds up the rate of reaction by lowering the activation energy
Describe the lock and key model
Active site and substrate have specific shapes which are complementary to each other, they bind to form an es complex which decreases the activation energy so product is released and enzyme is unchanged
Describe the induced fit model
Active site and substrate are almost complementary but become complementary when’s the es complex forms as the active site changes shape due to the es complex putting pressure on the bonds in the substrate which decrease the activation energy so product is released and enzyme is unchanged
How does enzyme concentration affect enzyme action
-Increasing enzyme concentration increases the number of active sites available for the substrate to bind with
-More ES-complexes can form as enzyme concentration increases
-The rate of reaction will increase until the amount of substrate becomes the limiting factor as there are more enzymes than substrate so increasing the enzyme concentration will have no more effect on the rate.
-The gradient can be used to calculate how fast the rate is changing
How does substrate concentration affect enzyme action
-Increasing the substrate concentration will increase the rate of reaction as there are more substrate molecules.
-More collisions so more ES-complexes will form.
-The rate of reaction will slow as the enzyme concentration becomes a limiting factor.
-When all the enzyme active sites are occupied (saturation point) increasing the substrate concentration will have no further effect on the rate.
How does temperature affect enzyme action
-As temperature increases so does the rate of reaction as there is more kinetic energy so the molecules move faster increasing the number of collisions and therefore the number of ES-complexes formed.
What happens to enzyme action when temperature goes beyond the optimum
-Each enzyme has an optimum temperature. Once this has been reached increasing the temperature further decreases the rate of reaction.
-At high temperatures the enzyme molecules vibrate too much, and bonds are broken which maintain the tertiary structure. The active site changes shape and no more ES-complexes can be formed as the substrate no longer fits. The enzyme is permanently denatured, the reaction stops
How does ph affect enzyme activity
All enzymes also have an optimum pH as well as temperature. Most work best at pH 7 but some work best at pH 2 (e.g pepsin in the stomach).
-Above and below the optimum pH for each enzyme the H+ ions and OH- ions disrupt the ionic and hydrogen bonds holding the enzyme’s tertiary structure in place.
What happens to enzyme activity when the ph goes beyond the optimum extremely
-At extremes of pH the active site changes shape and no more ES-complexes can be formed as the substrate no longer fits. The enzyme is permanently denatured, the reaction stops.
Name the 2 enzyme inhibitors
Competitive inhibitors
Non competitive inhibitors
What is a competitive inhibitor and what does it do
Have a similar shape to that of substrate molecules
Compete with the substrate to bind to the active site of the enzyme
They block the active site so the substrate cannot bind, and no ES complexes are formed
What is a non competitive inhibitor and what does it do
Do not bind to the active site as have different shape to the substrate so do not compete
Bind to a site away from the active site known as the allosteric site.
Causes the active site of the enzyme to change shape so it is no longer complimentary to the substrate so no ES complexes can be formed
How do competitive inhibitors affect enzyme action
-Increasing the substrate concentration still increases the rate of reaction.
-Increasing the concentration of substrate will reverse the effects of a competitive inhibitor as the substrate will out-compete the inhibitor for the active sites.
