Activators and Inhibitors

Hey guys, yesterday we finished our lecture on enzymes by talking about how activators and inhibitors affect enzyme activity. We also talked about allosteric regulation, cooperativity, metabolic pathways and how these pathways are efficient for the cell.

Enzyme activity is sensitive to the presence of specific substances that bind to the enzyme and cause conformational change in the enzyme (conformational change is the change in the shape of the molecule, in this case the active site of the enzyme). Through these substances, a cell is able to regulate which of its enzymes are active and which are inactive at a particular time. This allows the cell to increase its efficiency and to control changes in its characteristic during development.

The first type of substance that we will talk about is an activator which binds to the active site of the enzyme and increases the activity of the enzyme. Enzyme function is often assisted by additional chemical components known as cofactors and coenzymes.

Cofactors are non-protein, small inorganic compounds and ions. Inorganic compounds are compounds that do not have carbon to carbon bonds. These small molecules are usually metals and bind within the enzyme molecule. For example zinc is used by some enzymes to draw electrons away form their position in covalent bonds in the substrate, making the bonds less stable and easier to break the bonds between the substrate. *Remember glucose, it is stable and needs something to disrupt the bond well here the metals in the enzyme draw the electrons away from the substrate molecules, disrupting the bonds between the substrate.*

Coenzymes are nonprotein, organic molecules which are molecules that have carbon to carbon bonds. These molecules bind temporarily or permanently to the enzyme near its active site. Many vitamins are parts of coenzymes. In numerous ozidation reduction reactions that are catalyzed by enzymes, the electrons pass in pairs from the active site of the enzyme ot a coenzyme that serves as the electron acceptor. The coenzyme then trasfers the electrons to a different enzyme, which releases them to the substrates in another reaction. These electrons have energy with them. One of the most important coenzymes is the hydrogen acceptor nicotinamide adenine dinucleotide (NAD+).

Those were activators but there are also substances that bind to he an enzyme and decreases the activity of the enzyme and these substances are called inhibitors. There are four types of inhibition: competitive inhibition, noncompetitive inhibition, irreversible inhibition, and feedback inhibition.

competitive inhibitor

Competitive inhibitors compete with the substrate for the same active site, displacing a percentage of substrate molecules from the enzymes. One example of this type of inhibitors is the medicine penicillin. Penicillin blocks the enzyme bacteria use to build their cell wall. To overcome competitive inhibition is to increase the substrate concentration because if there is higher concentration of substrates than the inhibitor, then there would be more collisions between the enzyme and the substrate; the enzyme will more frequently collide with the substrate.

noncompetitive inhibitor

Noncompetitive inhibitors bind to the enzyme in a location other than the active site, changing the shape of the active site of the enzyme making the enzyme unable to bind to the substrate. Most noncompetitive inhibitors bind to a specific portion fo the enzyme called an allosteric site. A substance that binds ot an allosteric site and reduces enzyme activity si called an allosteric inhibitor. When this substance binds to this site, it causes a conformational change in the active site which is no longer a functional binding site.

Irreversible inhibitors are the same thing as competive and noncompetitive inhibitors, however irreversible inhibitors are inhibitors that permanently bind to the enzyme. So competitor would bind permanently to the active site while the allosteric (noncompetive) will permanently bind to the allosteric site of the enzyme.

Before we can talk about the last inhibitor, it is important if we get the understanding about metabolic pathways. Organisms contain thousands fo different kinds of enzymes that catalyze a wide variety fo reactions. Many of these reactions in a cell occur in sequences called metabolic or biochemical pathways. In such pathways, the product of one reaction becomes the substrate for the next reaction. Metabolic pathways creates organization and efficiency amongst the cell.

Now we can talk about feedback inhibition. Feedback inhibition is a process where the end production of a biochemical pathway acts as an inhibitor of an early reaction. Not only is it unnecessary to synthesize a compound when plenty is already present, but doing so would waste energy and raw materials. It is therefore advantageous for a cell to temporarily shut down biochemical pathways when their products are not needed and this is when feedback inhibition comes in. The end product of the pathway binds to an allosteric site on the enzyme that catalyzes the first reaction in the pathway, causing conformational change and preventing the enzyme from functioning properly.

For a better understanding of the biochemical pathway and the feedback inhibition please go to http://www.explorebiology.com/apbiology/resources/ and go under enzymes and metabolism and click on the second biochemical pathway animations.

Allosteric regulation is conformational changes by regulatory molecules like inhibitors that keep enzyme in an inactive form and activators that keep the enzyme in an active form. Cooperativity is when a substrate acts as an activator because it causes a conformational change in the enzyme and this makes it easier for other substrates to bind to the enzyme.

Well I hope I had helped you out.