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B2 C) Enzyme Rate of Reaction
B2 C) Enzyme Rate of Reaction
Enzymes are biological catalysts – biological means that they have been produced by us, and catalyst means that they speed up the rate of reactions without being used up/ changed during the reaction. The rate of reaction for enzymes is affected by temperature and pH.
Temperature
Enzymes in the human body have evolved to work best at normal body temperature, which is 37°C. At 37°C, the rate of reaction for enzymes will be the greatest – we say that 37°C is the enzyme’s optimal temperature. A temperature above or below 37°C results in a lower rate of reaction. The graph below shows how the rate of reaction for an enzyme changes as temperature increases.
Enzymes in the human body have evolved to work best at normal body temperature, which is 37°C. At 37°C, the rate of reaction for enzymes will be the greatest – we say that 37°C is the enzyme’s optimal temperature. A temperature above or below 37°C results in a lower rate of reaction. The graph below shows how the rate of reaction for an enzyme changes as temperature increases.
The rate of reaction increases as the temperature goes from 0°C to 37°C. This is because the greater temperature gives the substrates and enzymes more kinetic energy. This means that they move around faster, which leads to more frequent collisions between the enzymes and substrates. More frequent collisions means that there will be a greater rate of reaction as the temperature increases from 0°C to 37°C (the optimal temperature for human enzymes).
When the temperature goes above 37°C, the high temperature causes the bonds that make up the enzyme to break. This changes the shape of the active site, which means that the substrates can no longer fit into the active sites of the enzymes – this decreases the rate of reaction. This process is known as denaturing. A diagram of a normal enzyme and a denatured enzyme is shown below.
When the temperature goes above 37°C, the high temperature causes the bonds that make up the enzyme to break. This changes the shape of the active site, which means that the substrates can no longer fit into the active sites of the enzymes – this decreases the rate of reaction. This process is known as denaturing. A diagram of a normal enzyme and a denatured enzyme is shown below.
From the above diagram, you can see that the active site for the denatured enzyme has changed shape because the high temperature has broken the bonds in the enzyme. The changed shape for the active site of the denatured enzyme means that the substrates can no longer fit into the active site, which results in the rate of reaction decreasing. So, as the temperature goes above 37°C (the optimal), the rate of reaction decreases because the enzymes denature – the graph slopes downwards after 37°C.
pH
The rate of reaction for enzymes is also affected by pH, which goes from 0 to 14 – a value of 7 is neutral, values between 0 and 6 are acidic, and values between 8 and 14 are alkaline. Enzymes have evolved to work best at the pH of the cells that they are operating in – this pH is usually neutral (a pH of 7). The graph below shows how the rate of reaction for an enzyme that is found in cells that have a neutral pH (7) changes as pH increases.
The rate of reaction for enzymes is also affected by pH, which goes from 0 to 14 – a value of 7 is neutral, values between 0 and 6 are acidic, and values between 8 and 14 are alkaline. Enzymes have evolved to work best at the pH of the cells that they are operating in – this pH is usually neutral (a pH of 7). The graph below shows how the rate of reaction for an enzyme that is found in cells that have a neutral pH (7) changes as pH increases.
If the pH is above or below 7 (neutral), the rate of reaction falls. The rate of reaction falls because the pH interferes with the bonds in the enzyme, which changes the shape of the active site, thus meaning that the substrates can no longer fit into the active site of the enzyme, which results in the rate of reaction falling. This is known as denaturing and it happens on both sides of the optimal pH; for the enzyme above, denaturing happens when the pH is between 0 and 6, and when the pH is between 8 and 14.
The majority of enzymes in our body are found in neutral conditions and will therefore have an optimal pH of 7. However, some enzymes are found in conditions where the pH is not 7 and these enzymes will have a different optimal pH. For example, the enzyme pepsin is found in the stomach. The stomach produces hydrochloric acid, which makes the contents of the stomach very acidic. The enzyme pepsin has evolved to work best at a pH of 2, which is the pH of the stomach; the optimal pH for pepsin is 2. A pH away from 2 will result in pepsin denaturing, which reduces the rate of reaction.
The majority of enzymes in our body are found in neutral conditions and will therefore have an optimal pH of 7. However, some enzymes are found in conditions where the pH is not 7 and these enzymes will have a different optimal pH. For example, the enzyme pepsin is found in the stomach. The stomach produces hydrochloric acid, which makes the contents of the stomach very acidic. The enzyme pepsin has evolved to work best at a pH of 2, which is the pH of the stomach; the optimal pH for pepsin is 2. A pH away from 2 will result in pepsin denaturing, which reduces the rate of reaction.