The effects of temperature on catalase in yeast and liver.

Introduction & Theory:

As stated in the headline, this will be a plan to investigate the effects of temperature on the enzyme catalase in yeast and liver. But before I go in to detail about the experiment itself, the biology behind the reaction should be discussed. Starting with what will in great part control the reaction, some knowlegde of the biology of enzymes should be obtained.

As we have learned, enzymes may be described as globular proteins with catalytic properties. They cannot cause reactions to occur, but only speed up ones which would otherwise take place more slowly. While the enzyme molecule is normally larger than the substrate molecule it acts upon, only a small part of the enzyme, called the active site, actually comes into contact with the substrate. It is commonly accepted that the enzymes operate on a socalled lock and key mechanism. The lock and key mechanism works in the way that in same way as a lock fits a key, the substrate fits exactly into the active site of the enzyme molecule. There, the substrate is either split into two or more molecules, or two or more molecules may be joined together, as with dipeptide. During the entire process, the enzyme remains unchanged and maintains its initial shape. This allows it to keep turning sustrate into products, being used over and over again. The rate at which enzymes normally work can be shown on a graph as a rapid increase at first, as there is plenty of substrate for the enzymes to bump into and turn into product. At a point though, the reaction will reach its peak. A maximum number of substrate is being turned into product per second/minute. After this, the rate of which the process is taking place will decrease. With fewer substrates around for the enzymes to work on, the collisions are fewer and longer apart. After a while the process will come to a full stop as there are no more substrates to be turned into a certain product.

Also involved in forming products is the activation energy. This is the energy needed in many reactions to convert a substrate to a product. When a substrate locks to the active site of an enzyme, the shape of its molecule changes, which makes it easier to change into a product. The activation energy with enzyme is lower, making it economical to use as energy can be saved and the enzymes can be re-used.

Different factors can influence the working rate of an enzyme. These include enzyme concentration, substrate concentration, pH and temperature. As said above, we will be investigating the effects of the latter in this experiment, but we still have to take into account the possible influences of the others.

The effect of enzyme concentration:

The more enzyme present, the more active sites will be available for the substrate to lock into. The initial rate of a reaction will increase proportionally with enzyme concentration as long as there is plenty of substrate available. When there is no more substrate available to fit the lock and key, the addition of more enzymes will make no difference. There is simply no substrate available for them to collide into.

The effect of substrate concentration:

The more substrate molecules there are, the more often one can lock into the active site of an enzyme. In other words, as substrate concentration increases, the initial rate of reaction also increases. This is only up to a certain point though. As we go on increasing the substrate concentration, keeping the amount of enzymes the same, there comes a point where every enzyme's active site is working continuously. It cannot take on any more substrate at the present time, and the substrates litterally have to "queue up". At this point, we say the enzyme is working at its maximum possible rate, known as Vmax.

The effect of pH:

Most enzymes work best in neutral conditions, which is a pH of around 7. Some , for instance pepsin, have a different optimum pH, but they are the exception rather than the rule. pH is a measure of the concentration of H-ions in a solution, The higher the pH, the lower the H-ion concentration. A pH which differs greatly from the optimum pH could cause denaturation of an enzyme. The active site only needs a slight change to become unfittable with the substrate, which could happend as the H-ions interacting with the R-groups in ...