Discussion
This experiment is about the effect of pH in the activities of catalyse. A cork borer is used to cut out a potato cylinder from the potato. The potato cylinder was then cut into 10 disc shape with even thickness. A test tube was filled with 5 cm? of buffer solution and the 10 potato pieces were put into the test tube. 5 cm’ of hydrogen peroxide was measured and poured into the test tube. The delivery tube was then connected to a test tube of water. The reaction was shown where the bubbles had appeared. We are required to calculate the number of bubbles in the test tube. The experiment was conducted using different pH of buffer solution. The experiment was also repeated for each pH of buffer solution and the average readings were taken.
For pH 4.4 buffer solution, 4 bubbles were released at the first time, 6 bubbles were released at the second time and 1 bubble was released, the average bubbles released were 3.7. For pH 5.2 buffer solution, 5 bubbles were released at the first time, second time and the third time, the average bubbles released is 5. For pH 6.5, 5 bubbles were released at the first time, same to second time, 5 bubbles were released, and 6 bubbles were released at the third time, the average bubbles released were 5.3. For pH 7.5, 13 bubbles were released at the first time, 11 bubbles were released at the second time, 8 bubbles were released at the third time, the average bubbles released were 10.7.
Based on our result, the buffer solution that produced the most bubbles was buffer solution of pH7.5. Therefore, the optimum pH for starch to catalyse the reaction is pH 7.5. When the buffer solution of pH 4.4 was used, the bubbles released is the least because the pH is too low for the enzyme to catalyse the reaction. When the pH increases, the released bubbles also increases. When buffer solution of pH 7.5 was used, the released bubbles is the most. This had shown that buffer solution of pH 7.5 is the most suitable pH for the enzyme to carry out its reaction.
The activity of enzymes is affected by the acidity and alkality of the solutions they reacted. A slight change in pH can decrease the rate of enzyme-catalysed reactions as each enzyme only function at a particular pH.
Optimum pH is actually the pH at which an enzymatic or any other reaction or process is most effective under a given set of conditions. It is also defined as the pH at which the rate of enzymatic reaction is at its fastest. Different enzyme have different optimum pH where the enzyme need different pH value to carry out the reaction. In most of the cells, most enzymes function optimally at pH with the ranges of pH 6 to 8.
A change in the pH value can alter the charges on the active sites of an enzyme and the surface of the substrate. This can reduce the mobility of both molecules so that they will not bind with each other. If the pH value is low, the excess hydrogen ions will bind attach themselves with the active site of the enzymes. This causes the ionic charges on the active site altered. The substrate is unable to bind itself to the enzyme so reaction does not take place.
There are many examples of enzymes’ optimum pH. Pepsin is the enzyme of vertebrate pancreatic juice, which is produced in stomach. Pepsin’s optimum pH is pH 3 to 4. Pepsin is acidic to break down protein into smaller peptides. Another example is trypsin. The optimum pH for trypsin is pH 7. Trypsin is neutral and it is used to hydrolyse protein. Lipase is another example of enzyme. When lipase is presents in stomach, the optimum pH is pH 4 to 5 where it is used to break down fats into smaller molecules which is fatty acids and glycerol. When lipase is present in pancreas, the optimum pH is 8 where it is used to make pancreatic lipase that acts in the small intestine. The optimum pH of amylase is pH 4.6 to 5.2. When we chew the food in our mouth, amylase will convert the starch into maltose. The optimum of maltase is pH 6.1 to 6.8. It is used to catalyse the hydrolysis of the disaccharide maltose to the simple sugar glucose.
Throughout this experiment, we knew that each enzymes have its own optimum pH. Enzymes are important in our life such as it plays an important role in our digestive system.
Discussion
This experiment is about the effect of substrate concentration on enzyme activity. A cork borer is used to cut out a potato cylinder from the potato. The potato cylinder was then cut into 10 disc shape with even thickness by using a sharp scalpel and a ruler. 10 cm’ of 0.5 mol dm 3 hydrogen peroxide solution was filled into a test tube. The cut potato disc were put into the test tube and was shook gently. The test tube was later connected to another test tube filled with water. After 30 minutes, the number of bubbles released were calculated. The experiment was conducted using different concentration of hydrogen peroxide solution which is 1.0, 1.5, and 2.0 mol dm -3. The experiment was repeated for each concentration of hydrogen peroxide solution and the average reading will be taken so that the readings are more accurate.
When 0.5 mol dm 3 of hydrogen peroxide was used, the amount of bubbles released is 3 at the first time, 6 bubbles were released at the second time and 3 bubbles were released at the third time. Therefore the average bubbles released were 5. When 1.0 mol dm -3 of hydrogen peroxide was used, at the first time, 7 bubbles were released, 4 bubbles were released at the second time, 6 bubbles were released at the third time and the average amount of bubbles released were 5.7. When 1.5 mol dm } of hydrogen peroxide was used, the amount of bubbles released at the first time is 4, at the second time 8 bubbles were released, 16 bubbles were released at the third time. The average amount of the bubbles released were 9.3. When 2.0 mol dm-3 of hydrogen peroxide was used, 7 bubbles were released at the first time, 8 bubbles were released at the second time and 17 bubbles were released at the third time. The average bubbles released was 10.7.
Based on our result, we found that the hydrogen peroxide that produced the most amount of bubbles was hydrogen peroxide with concentration of 2.0 mol dm -3. It shown that the most suitable concentration for the enzyme to function in this experiment is 2.0 mol dm -3 of hydrogen peroxide. The hydrogen peroxide with concentration of 0.5 mol dm released the least bubbles. It is because the concentration is too low for the enzyme to catalyse the reaction.
The rate of an enzyme-catalysed reaction is directly proportional to the substrate concentration until the reaction reaches a maximum rate. Any increase rate in substrate concentration has no effect on the rate of reaction because the active sites of the enzyme molecules are fully occupied by the substrate molecules.
At low substrate concentration, a few of substrate molecules are present. There are many active sites which are available. Therefore, the rate of reaction increases direct proportional to the substrate concentration. The increases in substrate concentration means that more substrate molecules are available. Therefore there are more chances of collision between the substrate molecules and enzyme molecules to take place for a catalytic reaction. As more substrate molecules fill the active sites, more products are formed.
The increase in substrate concentration will only lead to an increase in the rate of reaction only if the enzyme molecules is enough and are available to catalyse the additional substrate molecules. There is a limit to how the rate of a reaction can be further increased by adding more substrate molecules to a fixed concentration of an enzyme. At a certain substrate concentration, the rate of reaction will not increase further and it becomes constant. It is because a reaction called maximum rate is reached. At this point, all the active sites are filled and engaged in catalysis. The enzyme molecules are saturated now. When the products leave an active site, another substrate molecule will enter the active site.
At high substrate concentration, there are more substrate molecules compared to enzyme molecules. The excess substrate molecules will have to compete with one another for the active sites. These sites will only become available until all the enzyme molecules have finished catalyzing the substrate molecules. When all the active sites are engaged in the catalysis of the substrate, the increase in the substrate concentration will not alter the rate of reaction so the rate of reaction becomes constant. At this point the enzyme has become the limiting factor in the reaction. The rate of reaction will only be increased if the enzyme concentration increase.
