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Activity of Diastase On Starch

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ACTIVITY OF DIASTASE ON STARCH Brief Starch is a polymer where the individual units in the polymer are glucose molecules. The most important enzyme that degrades starch is called diastase. This enzyme catalyses a split in the starch polymer so that eventually what is left over are short chains consisting of just a few glucose units (maltose). These can then be broken down by water so that the entire starch polymer is degraded to glucose. The glucose concentration that will be produced in a fixed time by the action of diastase on starch can be measured to find out the rate of hydrolysis of starch, as the equation below shows: STARCH DIASTASE GLUCOSE + MALTOSE The reaction between starch + water = glucose is called hydrolysis. In the chemical reaction that occurs, water is introduced into the bond between two glucose units with a -OH becoming part of one side of the bond and a hydrogen (H-) becoming attached to the other glucose molecule. Rate of hydrolysis of starch ? concentration of glucose produced (In the above relation time is kept constant) Glucose concentration can be measured by titrating glucose solution with quantitative Benedict solution having sodium carbonate in it. 25ml of quantitative Benedict solution+10 grams of sodium carbonate can be titrated with a solution having glucose in it. This titration gives us the volume of glucose solution used to carry out the titration. Subsequently we can find out the rate of hydrolysis of starch by comparing the concentration of glucose produced in one minute. So, lesser the volume of glucose solution used greater the concentration of glucose and faster the rate of hydrolysis of starch. ...read more.


pH Volume of reaction mixture used Rate of the reaction = 1/ volume of reaction mixture used 4 10.24 ml 0.0976 4.8 9.65 ml 0.104 5 9.35 ml 0.107 7 11.00 ml 0.0909 9 11.67 ml 0.0857 A graph of the rate of hydrolysis of starch against ph is shown below pH affects the three-dimensional structure of all enzymes. Enzymes are made up of amino acids. Each amino acid has a -NH2 group and a -COOH group, not to mention certain amino acids that have an extra -COOH group (e.g. aspartame) or an extra -NH3+group (e.g. asparagines). PH is all about concentration of H+ ions. At low pH and high H+ concentration the predominant forms of these groups will be -COOH and -NH3+ or the "protonated forms". At neutral pH the predominant forms will be -COO and -NH3+. At high pH the predominant forms will be -COO- and -NH2. However the actual pH at which each group becomes ionised depends on the particular amino acid and also the environment in which the enzyme is found. The usual way of expressing this is the pK value: this pK is the pH at which half of the groups are ionised. Interactions between these positive and negative charges are a very important part of what holds the structure together in an enzyme. These links are known as salt links, salt bridges or electrostatic interactions and involve a + to - attraction. Changing the pH therefore alters the properties of these salt bridges. Even a small shift away from optimum pH might mean one of these salt bridges is affected and therefore the shape and activity and stability of the protein will also be affected. ...read more.


Following results were obtained from these titrations. Titration readings using 1% starch solution. Titration no Initial reading Final reading Volume of solution used 1 1.00 13.6 12.6ml 2 13.6 25.7 12.7ml 3 25.7 38.4 12.7ml Mean volume of solution used = 12.6+12.7+12.7 = 12.67ml 3 Titration readings using 2% starch solution. Titration no Initial reading Final reading Volume of solution used 1 1.00 13.3 12.3ml 2 13.3 25.6 12.3ml 3 25.6 37.8 12.2ml Mean volume of solution used = 12.3+12.3+12.2 = 12.27 ml 3 Titration readings using 3% starch solution. Titration no Initial reading Final reading Volume of solution used 1 1.00 13.3 12.3ml 2 13.3 25.5 12.2ml 3 25.5 37.8 12.3ml Mean volume of solution used = 12.3+12.2+12.3 = 12.27ml 3 Effect of change in the concentration of starch on the rate of hydrolysis of starch Concentration of starch Volume of solution used Rate of hydrolysis of starch = 1/ volume of solution used 1% 12.67ml 0.0789 2% 12.27ml 0.0815 3% 12.27ml 0.0815 A graph of concentration of starch against rate is shown below These results shows that increasing the concentration of starch increases the rate of the reaction. This is because there are more molecules of starch present to be broken down, increasing the rate. However there comes a certain point whereby increasing the concentration of starch will no longer affect the rate of the reaction. From my results I can observe that this optimum stage at where this happens is when the concentration of the starch is at 2 and 3 percent. The reason for this is because all the active sites of the diastase enzyme were busy in breaking down the starch molecules, leaving no available active sites for new starch molecules. Therefore increasing the concentration of starch did not effect the rate of the reaction. ...read more.

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