Factors affecting enzyme activity

• Measuring enzyme activity:

  1. how fast the product is made - there are different molecules present at the end of a chemical reaction than there are at the beginning. By measuring the amount of end product present at different times during the experiment the reaction rate can be calculated
  2. how fast the substrate is broken down - to produce the end products in a reaction, substrate molecules have to be used up. By measuring the amount of substance molecules left at different times during the experiment, the reaction rate can be calculated
• Temperature: like any chemical reaction, the rate of an enzyme-controlled reaction increases when the temperature's increased
• More heat means more kinetic energy, so molecules move faster. This makes substrate molecules more likely to collide with the enzymes' active sites. The energy of these collisions also increases, which means each collision is more likely to result in a reaction
• If the temperature gets too high, the reaction stops
• The rise in temperature makes the enzyme's molecules vibrate more. If the temperature goes above a certain level, this vibration breaks some of the bonds that hold the enzyme in shape. The active site changes shape and the enzyme and substrate no longer fit together - the enzyme is denatured
• Denatured = no longer functions as a catalyst
• Every enzyme has an optimum temperature. For most human enzymes - 37 degrees, but some enzymes, like those used in biological washing powders, can work well at 60 degrees
• All enzymes have an optimum pH value. Most human enzymes work best at pH 7, but there are exceptions
• Pepsin works best at pH 2 (acidic) - which is useful because it is found in the stomach
• Above and below the optimum pH, the H+ and OH- ions found in acids and alkalis can disrupt the ionic bonds and hydrogen bonds that hold an enzyme's tertiary structure in place. The enzyme becomes denatured, and the active site changes shape.
• The higher the substrate concentration, the faster the reaction - more substrate molecules means a collision between substrate and enzyme is more likely and so more active sites will be occupied
• This is only true up until a 'saturation' point. After this point, there are so many substrate molecules that all the active sites are occupied - adding more makes no difference
• The more enzyme molecules there are in a solution, the more likely a substrate is to collide with one and form an enzyme-substrate complex. So increasing the concentration of the enzyme increases the rate of reaction
• But, if the amount of substrate is limited, there comes a point when there's more than enough enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect.