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3.6.3 Explain factors affecting enzyme activity

Temperature: As temperature increases so to does the kinetic energy of the enzyme and substrate molecules which randomly collide. The frequency of collisions increases as the temperature increases thus initially increasing the rate of reaction. This occurs up to a maximum rate of reaction and the temperature at which the maximum rate of reaction is reached is referred to as the optimum temperature. Beyond the optimum temperature, increasing temperature increases the kinetic energy of the molecules to the point that the three-dimensional shape of the enzyme can be lost. Thus the shape of its active site changes and can no longer bind to the substrate, reducing the rate of reaction beyond the optimum temperature.pH: All enzymes have an optimum pH at which they have their maximum rate of reaction. Increasing pH values are as a result of the addition of hydroxide ions (OH-) while decreasing pH values are as a result of the addition of hydrogen ions (H+). The addition of either OH- or H+ can change the charges of the amino acids that make up the polypeptide chains of the enzyme. This can alter the bonding in the protein and change the shape of the active site resulting in denaturation, or alternatively it can prevent the substrate from binding with the enzyme's active site. Therefore either increasing or decreasing pH from the optimum value results in decreasing rate of enzyme activity.Substrate concentration: When discussing substrate concentration it is assumed that enzyme concentration remains constant. When substrate concentration is increased the rate of enzyme activity increases as the enzyme's active sites are gradually filled through the increased number of collisions with the substrate (due to increased substrate concentration). However, there comes a point when all of the enzyme's active sites are bound with substrates and the enzyme's are working at their maximum rate of reaction. Any increase in substrate concentration beyond this point will not result in any additional increase in rate of enzyme activity.
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