A Level Biology Revision "Competitive Inhibitors" | Freesciencelessons YouTube Video Summary
This Freesciencelessons video covers competitive inhibitors, which are molecules that bind to the active site of an enzyme and prevent the substrate from binding. Competitive inhibitors compete with the substrate for the active site. By increasing the concentration of the substrate, the effect of the competitive inhibitor can be reduced.
Detailed Summary:
Competitive Inhibitors and Enzymes
This Freesciencelessons video explains that enzymes contain an active site, a groove on the surface of an enzyme, that is complementary to a specific substrate molecule. When the substrate perfectly fits into the active site, an enzyme-substrate complex is formed. The enzyme then catalyzes the reaction to form products. Once released, the enzyme is ready to bind to another substrate molecule to catalyze the reaction again.
Understanding Competitive Inhibitors
A key concept is understanding that the substrate is not the only molecule that can bind to the active site. There are molecules with similar, but not identical, structures to the substrate that can also bind to the active site. Because these molecules are not the substrate, no reaction happens, and after a short time, the molecule leaves the active site. By occupying the active site for a short time, the molecule prevents the actual substrate from colliding with the active site. This effect of the molecule is to reduce the rate of reaction. These molecules are called competitive inhibitors.
Succinate and Malonate
Succinate is the substrate for an enzyme involved in respiration. The molecule malonate has a similar structure to succinate and can act as a competitive inhibitor to prevent succinate from colliding with the active site of the enzyme, thus inhibiting respiration.
Reducing the Effect of Competitive Inhibitors
A competitive inhibitor competes with the substrate molecules for the active site. In order to reduce the effect of a competitive inhibitor, one can increase the concentration of the substrate. With an increase in concentration, there is a much greater chance that a substrate molecule will occupy the active site rather than a competitive inhibitor.
Competitive Inhibitor Graph
In an enzyme with no competitive inhibitor, as the substrate concentration increases, the rate of reaction increases in proportion. At a certain substrate concentration, the rate of reaction no longer increases because all of the active sites are occupied, and scientists refer to this maximum rate as Vmax. When there is a fixed concentration of a competitive inhibitor, the competitive inhibitor reduces the rate of reaction. By temporarily blocking the active site, the competitive inhibitor prevents the substrate from binding and forming an enzyme-substrate complex. However, as the substrate concentration increases, the effect of the competitive inhibitor reduces.
Drugs as Competitive Inhibitors
Many drugs are examples of competitive inhibitors, such as the drug methotrexate, which is used to treat certain cancers. Methotrexate is a reversible competitive inhibitor of an enzyme found in human cells. Another example is the antibiotic penicillin, which is a competitive inhibitor of an enzyme involved in the synthesis of bacterial cell walls. Penicillin binds irreversibly to the enzyme it inhibits. Some competitive inhibitors bind irreversibly to the active site of enzymes, and therefore, one cannot reverse the effect of these inhibitors by increasing the substrate concentration. Once an irreversible competitive inhibitor enters the active site, it never leaves.