pH is a measure of the hydrogen ion (H +) concentration. When there is a high concentration of H +, there is a low pH value and when there is a low concentration of H + there is a high pH value. A large amount of hydrogen and ionic bonds hold the tertiary structure of an enzyme protein in place. Therefore as a result the active site of the enzyme is held in the right shape. There is attraction between the oppositely charged groups on the amino acids in the enzyme protein which allow these bonds to occur.
Therefore by increasing or decreasing the concentration of hydrogen ions around the enzyme, the tertiary structure of the enzyme molecule can be altered. Consequently the shape of the active site changes due to the change in the charges around the active site, when the pH is changed, this in turn changes the rate of the enzyme-controlled reaction. This occurs because more hydrogen ions are attracted towards the negatively charged groups in the active site.
All enzymes have their own unique optimum pH, at which the rate of reaction is highest, which is generally pH7. At this optimum pH, an effective overall shape is given to the tertiary structure of the enzyme by the hydrogen ions. Therefore the active site is held in the best possible shape the substrate can complementarily fit into.
When the pH is changed, or the concentration of the hydrogen ions is modified, the reaction rate decreases rapidly. This is because the shape of the enzyme molecule is altered which in turn changes the shape of the active site. Enzymes are not denatured by minor changes in pH. If the pH is changed then it returns to its optimum then the bonds that have been broken can be re-formed. Therefore the chemical formula of the enzyme molecule is also affected by the pH.
Enzymes denature at 37-40egC. The rate of reaction of an enzyme-controlled reaction is increased when the temperature increases. However when the temperature carries on increasing the rate of reaction decreases, which leads to the enzyme not being able to function. The enzymes optimum temperature provides the maximum rate of reaction.
Competitive inhibitor molecules have a similar shape to the substrate molecules. Therefore they can occupy the active site allowing the formation of enzyme inhibitor complexes. Products are not formed from these because the inhibitors are not identical to the substrate. The reaction is not catalysed by the enzyme. A substrate molecule cannot enter when an inhibitor molecule is occupying an enzymes active site. Therefore there are a low amount of enzyme-substrate complexes and the rate of the reaction is reduced.
The level of inhibition is dependent on the concentration of the inhibitor and substrate. The level of inhibition decreases when the amounts of substrate molecules are increased. This is because a substrate molecule is more likely to collide with an active site than an inhibitor molecule.
There is no competition between non-competitive inhibitors and substrate molecules for a place within the active site. They attach on to the enzyme molecule in a location that is distant form the active site. This distorts the tertiary structure of the enzyme molecule which in turn changes the shape of the active site. Therefore the substrate can no longer fit into the active site, which prevents enzyme-substrate complexes from forming and the reaction rate s decreased.
The level of inhibition is dependent on the amount of inhibitor molecules present. The enzyme controlled reaction will halt if there are enough inhibitor molecules to bind to all the enzyme molecules present. This type of inhibition is not affected by changing the substrate concentration.
