Aim
To investigate the effect of increasing inhibitor concentration on the enzyme activity of catalase.
Underlying Biology
Enzymes have a hollow in their structure called an active site which allows enzymes to create an energetically favourable environment for biological reactions in the body’s metabolic pathways by lowering the activation energy. This is vital for life because the reaction rates needed to sustain life are very high and the body would perish if its temperature was increased to the levels needed to reach these reaction rates without enzymes. Instead, enzymes allow important metabolic pathways to function correctly and efficiently at normal body temperature.
A substrate joins to an enzyme’s active site in an enzyme reaction. Substrates have a high affinity for the enzyme’s active site, attracting them to the enzyme to attach to it, and when they join to the active site the enzyme’s structure changes to become better suited to the shape of the substrate. This process is called induced fit and it allows a more correct alignment of the enzyme and the substrate so that the reaction can take place.
The products produced from an enzyme reactions have a contrasting low affinity for the enzyme’s active site, which allows them to leave the enzyme’s active site.
An enzyme’s ability to function properly can be impeded by chemicals called inhibitors. There are two types of inhibitors: competitive and non-competitive inhibitors. Both types inhibit the enzyme by preventing the substrate from binding to the enzyme.
Competitive inhibitors compete with substrate molecule(s) to attach at an enzyme’s active site, as they both have a shape which allows them to fit into the active site. Once a competitive inhibitor binds to the active site, substrate molecule(s) are blocked from binding so the enzyme reaction cannot occur. Competitive inhibition can be reversed by increasing substrate concentration, because this allows more and more substrates to outcompete the inhibitors to bind to the enzyme active sites, until almost all active sites are occupied by a true substrate.
Non-competitive inhibitors attach to a site on the enzyme away from the active site, which causes the active site to change shape so that it is no longer suitable for the substrate(s) to bind to. This type of inhibition is not reversed by increasing substrate concentration because having more substrates present does not prevent non-competitive inhibitors binding to non active sites on the enzymes.
Another way inhibition can occur is end product or feedback inhibition, which allows metabolic pathways to be regulated. This happens when the end product of a metabolic pathway reaches a critical concentration. After this, the end product acts as an inhibitor for one of the earlier enzymes in the metabolic pathway blocking the pathway and preventing further synthesis of the end product.
Method
Piece of liver were added to four beakers with different copper nitrate concentrations, and four measuring cylinders were set up with hydrogen peroxide and detergent. Liver pieces from each beaker were added to a measuring cylinder and a set time was tracked with a stop clock. The volume of froth produced after a set duration was measured with the measuring cylinders. This was repeated at each copper nitrate concentration.
Results
