Effect of temperature, substrate concentration and pH on reaction rate
The rate of an enzyme-catalysed reaction is calculated by measuring the rate at which a A substance on which enzymes act. is used up or by the rate at which a product is formed.
Temperature
As with many chemical reactions, 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. This is shown in the graph below.
As the temperature increases so does the rate of enzyme activity. An The best or most appropriate - for instance, the conditions under which an enzyme works best (eg temperature and pH). activity is reached at the enzyme's optimum temperature. A continued increase in temperature results in a sharp decrease in activity as the enzyme's The part of the enzyme to which a specific substrate can attach or fit on to. changes shape. It is now denatured.
Effects of pH
Changes in Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. also alter the shape of an enzyme鈥檚 active site. Each enzyme work bests at a specific pH value. The optimum pH for an enzyme depends on where it normally works. For example, enzymes in the small intestine have an optimum pH of about 7.5, but stomach enzymes have an optimum pH of about 2.
In the graph above, as the pH increases so does the rate of enzyme activity. An optimum activity is reached at the enzyme鈥檚 optimum pH, pH 8 in this example. A continued increase in pH results in a sharp decrease in activity as the enzyme鈥檚 active site changes shape. It is now denatured.
Substrate concentration
Enzymes will work best if there is plenty of substrate. As the The concentration of a solution tells us how much of a substance is dissolved in water. The higher the concentration, the more particles of the substance are present. of the substrate increases, so does the rate of enzyme activity. However, the rate of enzyme activity does not increase forever. This is because a point will be reached when the enzymes become saturated and no more substrates can fit at any one time even though there is plenty of substrate available.
As the substrate concentration increases so does the rate of enzyme activity. An optimum rate is reached at the enzyme鈥檚 optimum substrate concentration. A continued increase in substrate concentration results in the same activity as there are not enough enzyme molecules available to break down the excess substrate molecules.