enzyme experiment a level biology

Biology A level revision resource: Reaction rates of enzymes

Living cells and organisms could not function without enzyme-controlled reactions. The more we understand about how enzymes function and the reactions they control, the better we can use the machinery of nature to benefit human endeavours.

How do you measure the rate of enzyme controlled reactions?

Enzymes operate throughout biological organisms, both intracellularly and extracellularly. You will be aware that enzymes are biological catalysts, meaning they increase the rate of chemical reactions without undergoing any permanent change. Enzymes are made from long chains of amino acids, folded precisely into a three dimensional shape (or tertiary structure) with an active site that allows it to operate as a catalyst. Any changes to this three dimensional structure can change the shape of the active site and cause the enzyme to become denatured. This structure is represented in the lock and key and induced-fit models of enzyme action, with the induced-fit model including the changes that can occur in enzyme shape to allow catalysis.

Given the range of enzyme controlled reactions, there is no single best method for measuring reaction rates as the products of reactions vary greatly. For example, catalase is a common intracellular enzyme that speeds the decomposition of hydrogen peroxide (a byproduct of metabolism) into water and oxygen. In this reaction the produced oxygen gas can be collected and used as a way of measuring the reaction rate. Alternatively, the extracellular enzyme tripsin breaks down casein in milk, changing its colour from white to clear. The reaction rate can therefore be measured with a colorimeter, which will indicate the absorbance of light through the product. The spectrophotometer shown below is similar to a colorimeter, although it measures the transmission, rather than the absorption of light.