Enzymes Flashcards
What is an enzyme?
A globular protein that catalyses metabolic reactions.
Where do enzymes function?
Inside and outside cels.
Mode of action of enzymes
An enzyme attracts substrates to its active site, catalyzes the chemical reaction by which products are formed, and then allows the products to dissociate.
Lock-and-key theory
The enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.
Induced fit theory
States that the binding of a substrate or some other molecule to an enzyme causes a change in the shape of the enzyme so as to enhance or inhibit its activity.
How does temperature affect enzyme action?
The rate of an enzyme-catalysed reaction increases as the temperature increases. However, at high temperatures the rate decreases again because the enzyme becomes denatured and can no longer function.
How does pH affect enzyme action?
Enzymes are also sensitive to pH . Changing the pH of its surroundings will also change the shape of the active site of an enzyme. All enzymes have an optimum pH value, so above or below the optimum pH, the H+ and OH- ions found in acids and alkalis can mess up the ionic bonds and hydrogen bonds.
How does enzyme concentration affect enzyme action?
Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to.
How does inhibitor concentration affect enxyme action?
The competitive inhibitor binds to the active site and prevents the substrate from binding there. The noncompetitive inhibitor binds to a different site on the enzyme; it doesn’t block substrate binding, but it causes other changes in the enzyme so that it can no longer catalyze the reaction efficiently.
For what is the Vmax used?
To derive the Michaelis-Menten constant (Km).
For what is the Km used?
To compare the affinity of different enzymes for their substrates.
Effects of inhibitors on the rate of enzymes
By binding to enzymes’ active sites, inhibitors reduce the compatibility of substrate and enzyme and this leads to the inhibition of Enzyme-Substrate complexes’ formation, preventing the catalysis of reactions and decreasing (at times to zero) the amount of product produced by a reaction.
Effect of immobilising an enzyme in alginate
May show selectively altered chemical or physical properties, and it may provide a better environment for the enzyme activity. Therefore, immobilized enzymes are often more stable than free enzymes in a solution.
