Introduction Enzymes are types of proteins that exist in living organisms to catalyse reactions which break down the enzyme’s substrate into its component parts. Enzymes do this by binding onto the substrate with the active site of the enzyme. This is the specific part of the enzyme designed to break down the substrate. The active site of the enzyme is specifically shaped to only accept one substrate meaning that only one (or very few) molecules can be broken down by any one type of enzyme. This can be illustrated by the lock and key analogy which was made popular by Emil Fischer in 1894.

In this analogy the enzyme is a lock into which a key (substrate) fits. If the substrate is the wrong size or shape it will not fit into the lock and thus the lock will not open (the substrate will not be broken down). Below is a diagram explaining the lock and key analogy. In this project I have chosen to investigate the factors which affect the reaction rate of the enzyme catalase. I have chosen this enzyme as after researching several enzymes I discovered that this particular enzyme is very common, it is found in the peroxisomes of nearly all human cells and is particularly abundant in mammalian livers.

Catalase is also found in vegetables such as potatoes. I have decided to use either liver, potato or apple in a suspension to use in my experiments as they contain catalase and can be suspended in water so I can conduct my experiments with relative ease. Although oxygen is vital for human survival excess oxygen is in fact very dangerous to the human body. Within the cells electrons are continually shuttled around by carrier molecules. When oxygen molecules collide with these carrier molecules they can react to form compounds which are often dangerous.

One such molecule is hydrogen peroxide (H2O2) which can attack delicate sulphur atoms and metal ions in proteins thus making it a very dangerous substance to have present in the human body. To combat this the enzyme catalase is used to break down toxic hydrogen peroxide into harmless oxygen and water. The reaction which takes place is as follows: Put simply two molecules of hydrogen peroxide liquid are broken down by catalase into one molecule of oxygen gas and two molecules of water.

In the following experiment I will investigate a factor affecting the reaction rate of catalase, after taking numerous results I will analyse them and come to conclusions regarding the relationship between the factor I investigate and the rate at which catalase reacts with hydrogen peroxide. Further Theory The mechanism by which the enzyme breaks down its substrate relies heavily on collision theory. This theory states that for the substrate to be broken down by the enzyme the two must collide. However, this is more complicated than it sounds.

For a reaction to take place the right part of the substrate must collide with the active site of the enzyme. Also, a certain amount of energy is needed to start the reaction. This is called the activation energy. If the substrate does not collide with the active site of the enzyme with sufficient energy the two will simply bounce off each other. This means that if there is a higher concentration of enzymes it is more likely that these will collisions will take place and therefore it is likely that the rate of reaction would be higher than if there were a lower concentration of enzymes.

Enzymes are made up of several amino acids joined together to form a polypeptide chain. These amino acids are held together by several different bonds, namely hydrogen bonds, disulphide bonds, ionic bonds and hydrophobic bonds. These bonds make certain molecules within the polypeptide chain slightly charged. Opposite charges attract causing the chain to fold over in several different places forming a globular shape. This also forms the specific shape for the active site of enzymes. If these bonds were to be broken the active site would lose its shape and so could not accept its substrate rendering it useless.

This is called denaturing and can be caused by several different factors. Two of these are temperature and pH. If the temperature of the enzyme is raised too much the enzyme will have too much energy moving the bonds and breaking them apart denaturing the enzyme. Also, if the pH is not the right ph for the specific enzyme then there will either be too many OH- ions or too many H+ ions which will disrupt hydrogen bonds thus denaturing the enzyme. Key factors investigating the rate of enzyme activity.

After conducting extensive research into the factors affecting enzyme activity I discovered that there were several different factors, four of which I could feasibly investigate in the school laboratory. These four factors were temperature, pH, concentration of substrate (hydrogen peroxide) and concentration of the enzyme solution (catalase solution). I think temperature would affect the rate of enzyme activity as all enzymes have an optimum temperature at which they work best, the reason for this is explained in the further theory section.