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Factors That Affect Enzyme Activity

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FACTORS THAT AFFECT ENZYME ACTIVITY Enzymes are biological catalysts, which speed up the rate of reactions. These catalysts are essential to life as most biological reactions would take place too slowly for life to exist. For example the oxidation of glucose to CO2 and H2O is relatively quick and proceeds almost completely in the direction stated. However, without enzymes, glucose oxidation occurs too slowly at physiological temperatures that the rate is essentially immeasurable. The increase in rate of reaction achieved by the enzymes, depending on the enzyme and reaction, range from a minimum of about a million to as much as a trillion times faster than the un-catalyzed reaction at equivalent concentrations and temperatures. Another significant advantage of enzymes is the fact that they are specific, they only catalyse specific substrates, depending on their shape and the enzymes active site shape. There are substrate concentration, pH, enzyme concentration, temperature, and the presence of inhibitors. Substrate Concentration At very low substrate concentration, collisions between enzyme and substrate molecules are infrequent, due to the decrease in the number of substrate molecules for the enzymes to catalyse, and therefore the reaction proceeds slowly. As the substrate concentration increases, the reaction rate initially increases proportionally as collisions between enzyme molecules and substrate molecules become more frequent, due to the increased number of substrate molecules that the enzymes can break down. ...read more.


This is why enzymes have an optimal temperature, which is the maximum working temperature for the enzymes without being too high as to denature it. The enzymes denature, as the molecules or polypeptide chains that make them up vibrate more and more, until they gain sufficient energy to break their bonds, which holds the enzyme in its shape (that makes it able to accept only substrates of certain shapes), therefore id the bonds are broken, the enzymes tertiary and quaternary structures are changed permanently, and it cannot accept substrate molecules. Effect of pH on enzyme activity Different enzymes have a different optimal pH, which is the pH in which the enzyme catalyses substrate at its fastest rate. If the pH is lower or higher than this, then the reaction rate dramatically decreases until it is eventually nil. For example, the enzyme pepsin has an optimal pH of 2, any higher than this, and the reaction rate dramatically decreases, as shown below. Beyond the optimal pH, the enzyme is denatured, which results in the changing of the active site and therefore inability of the enzyme to accept the substrate molecules to break down. The reason the enzyme denatures due to the bonding that determines the tertiary and quaternary structures being affected, namely the hydrogen bonding between the R groups, and also the ionic bonding involved in holding and stabilizing the structures. ...read more.


Non-competitive inhibitors are molecules that fit into another part of the enzyme, not the active site, and change the shape of the active site there. These are non competitive, as they do not compete with the substrate for the active site. These non-competitive inhibitors decrease the reaction rate considerably due to the fact that no substrate molecules can stop them from bonding to the part of the enzyme that they do. Substrate inhibition occurs where there is such a high number of substrate molecules that they actually block each other from access to the active site, therefore reducing the number of substrate molecules broken down. The concentration of substrate molecules must be extremely high for this to happen, but when it does, it affects the reaction rate considerably. Feedback inhibition occurs where a product of enzyme catalysis is either a non-competitive inhibitor of an enzyme, or is a competitive inhibitor for another enzyme in the chain of enzymes, therefore the reaction rate can reach a maximum, no matter how high the substrate or enzyme concentration, as the increased products that this produces results in more products that are inhibitors made which directly decreases the rate of reaction proportionally. ...read more.

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