An investigation into what happens when hydrogen peroxide is broken down by an enzyme found in yeast called catalase
AS Biology Coursework Katie Man
The effect of different substrate concentrations on the rate of reaction.
My aim is to investigate what happens when concentration of Hydrogen Peroxide is changed and how it affects the rate of reaction when it is broken down by the enzyme catalase (H2O2 → 2H2O + O2)
Scientific knowledge.
Enzymes are biological catalysts, regulating the rate at which chemical reactions take place without the enzyme being altered in the process.
Enzymes bind temporarily to one or more of the substrate molecules of the reaction they catalyse.
Enzymes work by lowering the activation energy required for a reaction to proceed. In order to do so, and enzyme molecule must unite - even if very briefly - with the substrate molecule(s). Enzymes are able to do this because an area of their structure matches to the substrate. This area is called the active site and is complementary in shape, charge and hydrophobic/hydrophilic areas. The substrate attaches to the active site by a random collision but is held briefly by hydrogen bonds, ionic and hydrophobic interactions. Because the substrate must fit into the active site the mode of enzyme action is comparable to a lock and key.
Sometimes the substrate attaches to the active site and triggers a shape change in the enzyme molecule which improves the fit further and causes the reaction to occur. This is referred to as induced fit.
The requirement for complementarity in the configuration of substrate and enzyme explains the remarkable specificity of most enzymes. Generally, a given enzyme is able to catalyse only a single chemical reaction or, at most, a few reactions involving substrates with very similar molecular structures.
The activity of catalase is strongly affected by changes in pH, and temperature. Each catalase molecule works best at a certain pH and temperature. The values for pH, and temperature, which give an enzymes greatest rate of reaction, are known as the optimum values. The activity of enzymes decreases away from these values. This is due to the importance of the tertiary structure in its function.
As the temperature of the solution containing the hydrogen peroxide and catalase molecules increases so does the rate of reaction. This occurs because as the temperature increases the kinetic energy of the molecules also increases. As the molecules are moving around faster there are more collisions which lead to reactions between catalase molecules, and hydrogen peroxide molecules. This effect continues up to the optimum temperature. Above the optimum temperature, the rate of reaction decreases, as the increasing kinetic energy causes the hydrogen bonds, holding the structure of the enzyme together, to break. This causes the active site to change shape. This is known as denaturation. The hydrogen peroxide substrate molecule can therefore no longer fit the active site, and the rate of reaction decreases until all the catalase molecules are denatured, and the rate of reaction is zero.
