INTRODUCTION

An enzyme is a biological catalyst (Purchon 2012). Its most common function is to speed up the rate of reaction. Without the existence of enzymes within living organisms, the process of digestion would take weeks and the function of our muscles,nerves and bones will decrease in efficiency (Purchon 2012). Therefore the activities in living systems are controlled through and dependent on enzymes. Similar to other catalysts, enzymes can be reused multiple times, however their natural properties are easily taken away or altered by heat (Purchon 2012). In order for enzymes to maintain their natural qualities, they must exist in body temperature and a specific pH (Purchon 2012). The reason why enzymes are so sensitive to heat and pH is because they are protein molecules in nature (Purchon 2012). Enzymes works they bind themselves to one reactant also known as a substrate, by doing this they are lowering the activation energy of the reaction that they are catalyzing, hence the speed of reaction is increased. There are many different types of enzymes within living organisms catalyzing specific chemical reactions.

In this particular experiment, the enzyme pepsin was used. First recognized in 1836,pepsin is a digestive enzyme found in the gastric juices of the stomach of living organisms, mainly mammals (Pepsin 2012). It breaks down protein in foods such as meat, eggs, seeds and dairy products into peptides. Pepsin is formed by the release of pepsinogen in the stomach (Pepsin 2012). This is sparked by impulses from nerves and hormonal secretions of gastrin and secretin. The pepsinogen then is exposed to and mixes with the hydrochloric acid and rapidly unfolds and breaks, converting into pepsin(Pepsin 2012). To break proteins into basic amino acid molecules,the peptide bonds must be broken first (Hendrickson 2010). The reaction that breaks these bonds is called hydrolysis, as a water molecule is required in order for the peptide bonds to split (Hendrickson 2011).

During this reaction the peptide bond breaks, simultaneously the water molecule splits and a new bond is formed with one of the amino acids and the hydrogen atom from water, the other amino acid forms a bond with the other hydrogen atom and an oxygen atom present (Hendrickson 2011). Pepsin speeds up the hydrolysis of protein and makes this reaction more effective(Hendrickson 2011). Pepsin performs most proficiently at pH of 1- 3, which is the normal acidity of gastric juices (Pepsin 2012). Any pH higher than that,the enzyme will cease to function properly (Hendrickson 2010). The enzyme is important for the absorption of nutrition from the protein consumed. The absence of pepsin would cause the digestive tract to move the food eaten through the stomach and intestine very quickly and would not give the body enough time to absorb the nutrition, as the rate of the hydrolysis reaction is too slow without pepsin (Hendrickson 2010).

The aim of this experiment is to investigate the effect of different pH levels on the activity of pepsin on proteins. The protein that we used was egg white. The main objective was to model the activity of pepsin in the stomach by showing its actions on protein by simulating the effect with pepsin and egg whites. The experiment was carried out at a number of pH levels to show that pepsin (and all other enzymes) have an optimal pH range in which they perform most effectively, in order to model the effect the changing pH has on the activity of the enzyme. Enzyme has an optimal pH range and anything outside this range inhibits its activity(Hendrickson 2010), therefore it was proved that the lower the pH, the faster the rate of enzyme reaction activity. Pepsin has an optimal range of pH 3(Pepsin 2012), which is highly acidic and is found in the stomach of the human body where it digests proteins. This means that any pH less acidic or more basic than this level will not allow the reaction to occur, as these are not the optimal conditions for the activity of the enzyme.

Methodology

5 test tubes were collected, labeled one to six and placed on a test tube rack. In each of the labeled test tubes 5cm3 of egg – white suspension was placed into it using a clean pasteur pipette. Test tube labeled one had 2cm3 sodium carbonate solution. 0. 5cm3 sodium carbonate solution was added to test tube 2 and test tube 3 had nothing which was used as a control. 1cm3 and 2cm3 of HCL was added into test tubes 4 and 5 respectively, using Pasteur pipettes. 1cm3 of pepsin was added into each test tube 1 using a clean Pasteur pipette. Results Testtube Egg-white suspensionand pepsin PH Appearance of contents after 5minutes 1 2cm3 sodium carbonate solution 9 Remain unchanged 2 0. 5cm3 sodium carbonate solution 8. 9 Remain unchanged 3 Nothing 7. 4 Slightly off-white colour observed 4 1cm3 HCL 3. 9 Off-white colour observed 5 2m3 HCL 3. 1 Off-white colour observed

Discussion

The results from this experiment support the hypothesized statement. It was hypothesized that the lower the pH, the faster the rate of enzyme reaction (pepsin)activity and this was proven to be true, the average time for pepsin to render the egg-white suspension clear was lowest at the lower pH of 0 and 3. The PH 3 made pepsin to turn to the egg white suspension off white this makes sense because it is stated above that pepsin has an optimal range of pH 1-3 (Pepsin 2012). Therefore the results obtained suggest that any pH above 3 will inhibit the function of pepsin and stops the reaction between egg white and pepsin or makes it move very slowly. According to the results obtained from this experiment pepsin works best at pH 3. This is true as pepsin performs most proficiently at a pH of 1 – 3, which is the normal acidity of gastric juices (Pepsin2012).

Therefore any pH below or above this range will inhibit or slow down the function of pepsin. The major sources of possible error was our PH meters which doesn’t function well so there was a need to take more PH readings. During the experiment there were different people within the group guessing when the egg white had turned off white and in order to improve this error maybe one person should have been nominated to make this judgment so that all the results were consistent throughout the whole experiment. In order to maintain accuracy there were a few things that were controlled such as the amount pepsin, egg white and acid or buffer solution used. The type of instrument to measure all of these solutions, which was a clean Pasteur pipette. To avoid contamination, a different pipette was used for each type of solution.

CONCLUSION

The experiment was easy to carry out. During this experiment, quite few things was learnt about the enzyme pepsin, its purpose, function and the environment as to which it works best in.