An enzyme has an active site, which has a unique shape into which only a substrate of the exact same unique shape can fit. When this substrate fits into the active site it forms an enzyme-substrate complex: Enzymes can be denatured at certain conditions. These conditions are high temperatures and extreme levels of pH. The bonds that hold enzymes together are quite weak and so are easily broken by the above conditions. When these bonds are broken the enzyme, along with the active site, is deformed, thus deactivating the enzyme. This is know as a denatured enzyme:
The Effect of Enzyme Concentration:
Rate of Reaction
The rate of reaction is directly proportional to the enzyme concentration when the substrate is in excess. This is due to the fact that when the enzyme concentration is raised it makes more active sites available to react with the substrate.
The Effect of Substrate Concentration:
As you can see from the graph, at low substrate concentrations the rate of reaction is directly proportional to the substrate concentration due to the fact that when the substrate concentration is increased the rate of enzyme-substrate collisions (reaction) is equally increased. However, as the substrate concentration rises the rate of reaction will finally reach a maximum level. This is because all the active sites are saturated with substrate. The Effect of Temperature: Optimum Temperature
0 10 20 30 40 50 60 70 80 90 100
Temperature /°C At the lower temperatures, the rate of reaction rises with a very steep gradient as the temperature increases (0-36°C). This is because the molecules of the enzyme move faster and faster thus causing the rate of enzyme-substrate collisions to increase. We know that the rate of reaction doubles every 10°C. This can be shown by:
Q10 = 2 The temperature rises to such a degree that the enzyme becomes denatured. This is because the molecules of the enzyme vibrate so violently that they break their weak bonds holding the structure of the enzyme together. As shown in the graph, the perfect temperature for the majority of enzymes is 37ºC. For this reason, our body temperature is 37°C
The Effect of pH:
Rate of Optimum
0 3 5 7 9 11 13
pH With a change of pH the weak bonds holding the enzyme together will break. This will denature the enzyme, thus deactivating the active site. As enzymes normally exist within cells where the pH is 7, the most favourable pH is obviously 7. As you can see from the graph, a pH significantly higher or lower than 7 will kill the cells.