Studying the Effect of pH on the Activity of Pepsin

c



Studying the effect of pH on the activity of pepsin  oblem statement : What are the effects of pH on the activity of pepsin? Va iables Manipulated variable : pH of medium Responding variable : Rate of enzymatic reaction Fixed variable : Volume and concentration of albumne suspension Hypothesis The optimum pH for the activity of pepsin is an acidic medium of pH 3 Mate ials Albumen suspension, 1% pepsin solution, 0.1 M hydrochloric acid, 0.1 M sodium hydroxide solution and distilled water. Appa atus Beakers, droppers, thermometers, test tubes, 5 ml syringes, pH paper, wire gauze, a stopwatch and a test-tube rack. Technique Observe and record the condition of mixture before and after 20 minutes.  ocedu e 1. An albumen suspension is prepared by mixing the egg white from an egg, with 500 ml of distilled water. The suspension is boiled and cooled down. Large particles are removed by using glass wool. 2. Three test tubes are prepared and labeled P, Q and R respectively. 3. A syringe is used to add 5 ml of the albumen suspension to each test tube. 4. The solution below are added to the test tubes.



P: 1 ml of 0.1 M hydrochloric acid + 1 ml of 1% pepsin solution.




Q: 1 ml of distilled water + 1 ml of 1% epsin solution. R: 1 ml of 0.1 M sodium hydroxide
solution +1 ml of 1% pepsin







c



Figure 1 5. A piece of pH paper is dipped into each test tube and the pH value is determined and recorded. 6. All the test tubes are immersed in a water bath maintained at 37 C for 20 minutes. (Figure 1) 7. The conditions of the mixtures are observed at the beginning of the experiment and again after 30 minutes. 8. The result are recorded in a table Result: Mixture Test tube

pH

P

3

Q

7

Cloudy

Cloudy

R

8

cloudy

Cloudy

At the beginning of the experiment Cloudy

After 20 minutes Cloudy

üiscussion: 1. The test tube are immersed in the water bath maintained at 37 C because that is the optimum temperature for the action of pepsin 2. Pepsin, hydrolyses albumen (a protein) into polypeptides in an acidic medium. This solution turns clear because polypeptides are soluble in water. 3. (a) The pH condition in test tube P (pH 3) is optimum for the function of pepsin (b) This is because the contents of test tube P become clear at the end of the experiment. (c) this shows that albumen has been digested or hydrolysed by pepsin.

c



4. (a) The content of test tubes Q and R are still cloudy at the end of the experiment (b) This shows that a neutral (test tube Q) and an alkaline pH (test tube R) are not suitable for the activity of pepsin  onclusion : The activity of pepsin is affected by the pH of its medium. An acidic medium (pH 3) is the most suitable medium for pepsin to function effectively. The hypothesis is accepted