What influence does pH have on the enzyme Catalase?

Authors Avatar

Anna Broadley                BIOLOGY DATA ANALYSIS

UVC

Biology Data Analysis

What influence does pH have on the enzyme Catalase?

_____________________________________________________________________________

Enzymes act as catalysts in the cells of an organism, speeding up a chemical reaction but remaining unchanged itself. Most enzymes break down large molecules into small molecules. However, others can join small molecules together. Enzymes are important in an organism because they regulate the many chemical reactions that take place inside the cells in the process of metabolism. They are proteins, made of long chains of amino acids folded into a complex shape called a globular protein.

The molecules in the reaction, called the substrate, must fit exactly into the enzyme in a place called the active site, which is where the reaction takes place, for the enzyme to work. Changes in the environment the enzyme, for example temperature or pH, can affect the active site shape and therefore they change the rate of reaction.

This data analysis was to investigate the influence of pH on the rate of reaction of the enzyme catalase in potatoes. Catalase breaks down the highly oxidising hydrogen peroxide, into water and oxygen.

2H2O      CATALASE     2H2O + O2

Hydrogen peroxide is formed as a by-product of various other biochemical reactions and would damage cell membranes very quickly if not removed, so catalase is an essential enzyme to work quickly and effectively. Catalase occurs in many plant and animal tissues, but this experiment used the catalase in potatoes.

During the experiment, potato discs which naturally contain catalase were placed in a solution of a known pH and hydrogen peroxide. Then the rate at which oxygen produced evolved the manometer liquid within twenty seconds was measured. The oxygen production proved that there was a reaction taking place and the movement reflected the rate of reaction of the catalase in the potato, measured in mm/20s. The class used eight different potatoes at a range of pH values from pH 4 to pH 8.

Results

The following table displays the results taken, with the range of the values at each pH and the mean result from each pH indicated on the right hand side.

I plotted this mean with error bars to display the range on the graph (Figure 1)

I then worked out the minimum, lower quartile, medium, upper quartile and maximum value from the results at each pH, shown in this second table. I plotted these in the form of a box and whisker diagram on my graph (Figure 2) to display the distribution of the data collected.

Summery of Evidence

The set of results show that pH clearly does have a great effect on the activity of enzymes. The data shows that the enzyme catalase causes a reaction at the range of pH values we trialled, showing catalase can catalyse the reaction between pH 4 and 8.

Moreover, they show a trend that as the pH buffer was increased; more oxygen was made and evolved the manometer liquid showing that rate of reaction between catalase and hydrogen peroxide increased. Figure 1 represents this with the positive correlation of the curve. The values also concur with the trend. For example, at pH 4 the mean reading was 20mm/20s, but at pH it was 64mm/20s. This shows that the rate roughly tripled between pH 4 and pH 8, showing a clear increase.

The quickest rate of reaction was at pH 8, where the mean result was 64mm/20s.

However, the rate of reaction did not increase at a constant or directly proportional rate, increasing in reaction the same amount with increase pH, or exponentially like some chemical reactions. However, it rose in three stages, which are shown in the line of best fit in Figure 1. It went very steeply to begin with between the most acidic pH 4 and 6, rising very quickly 17mm/20s between the means of pH 4 and 5, and still sharply with a growth of 25 mm/20s between pH 5 and 6 (42mm/20s overall between pH 4 and 6). The curve then begins to slow down between pH 6 and 7 as the pH became neutral, with the mean values only increasing 1mm/20s. Finally it flattens out between pH 7 and 8. A few potatoes increase a little. Potato 4 has an average of 34mm/20s at pH 7 and 37mm/20s and pH8. However, some decreased a little. Potato 8 went from 65mm/20s at pH 7 to 56mm/20s at pH 8. This shows that the data peaked at its maximum somewhere between pH 7 and 8.

There were three measurements from the table which I considered to be outliers as they did not follow the increasing trend at one pH that all the other potatoes did and although was generally a lot of spread between the data and varying ranges of rate of reaction, these three were more than double the next highest rate.

Therefore the conclusion of my results is that although the enzyme catalase works at a low pH 4, the rate of reaction is much higher, and consequently the enzyme is more effective, when the pH is increased. The pH where the relative rate of reaction was most high at the values we investigated was pH 8. This shows that the optimum pH, where catalase breaks down hydrogen peroxide most effectively, is approximately around pH 8. However, the rate of reaction begins to slow down and effectively flattens out between pH 7 and 8. In fact with potatoes 1, 7 and 8 the results for pH 8 were lower than the results for pH 7. This shows that the increase in the rate of reaction which the increase of pH causes is not permanent and that it is likely the other potatoes will not increase any more or little after pH 8. This suggests that when the pH is more alkali than pH 8, the enzyme activity is reduced and therefore the rate of reaction should decrease. It suggests that the curve were to continue it is likely it would be bell shaped.

Join now!

Limitations to the conclusion

However, there are also some limitations to my conclusion due to the extent of my data, which could affect the confidence I can place in it. This relationship of the rate of reaction increasing is not definite as the error bounds showing the range of results overlap, showing that the true rate of reaction theoretically could be the same at pH 5, 6, 7 and 8. However, the box and whisker plots in Figure 2 show that the majority of the data in the boxes (representing 50% of the results) do not overlap. There is a ...

This is a preview of the whole essay