The name of enzyme involved in this experiment is salivary amylase, which presents in our saliva. Salivary amylase catalyses the breakdown of complex sugar, such as starch, into a simple sugar, such as glucose. In this experiment, the optimum temperature for salivary amylase to function is 37˚C. Above the optimum temperature, the kinetic energy in the substrate and enzyme increases.
The number of collisions between substrate and enzyme also increases, but the formation of enzyme-substrate complex decreases. This is because the increasing of kinetic energy causes the amino acid molecules to vibrate violently. Some bonds like hydrogen and ionic bonds which hold the configuration of the enzyme break. The shape of active site of the enzyme changes and is not able to bind with the substrate anymore. 3D structure of the enzyme is said to be destroyed. Thus, the enzyme denatures at high temperature and loses its catalytic activity permanently.
Hydrochloric acid, HCL in this experiment is used to hydrolyze the complex sugar which present in solution B into monomers or simpler sugars. At 37˚C, salivary amylase present in saliva reacts actively to hydrolyze the complex sugar in solution B as 37˚C is its optimum temperature. Therefore, it gives positive result for the Benedict’s test, which is formed brick-red precipitate. However, at the same temperature, hydrochloric acid gives negative result as it is unable to hydrolyze the content in solution B. At 95˚C, hydrochloric acid has obtained enough activation energy and breaks the bonds of complex sugar in solution B into simpler sugars.
Thus, it produces positive result for Benedict’s test. Inversely, salivary amylase is denatured at 95˚C and unable to react normally with substrate in solution B and therefore, the result for Benedict’s test is negative. The product formed when 10ml of solution B and 1ml of saliva react at 37˚C is monosaccharide. The product formed when 10ml of solution B and 1ml of 3M hydrochloric acid react at 95˚C is monosaccharide too. Solution A gives positive result for Benedict’s test, which indicates it is one of the reducing sugars and the negative result for iodine test shows that starch is absent in solution A. In solution B, reducing sugar is absent because the result for Benedict’s test is negative. However, the result for iodine test is positive, which indicates starch is present in solution B.
In test tubes 1 and 3, reducing sugar is present after reacted in 37˚C and 95˚C respectively because it show positive result when tested with Benedict’s reagent. So, the structure of the sugar in solution A is simpler, while the structure of the sugar in solution B is more complex as it needs salivary amylase or hydrochloric acid to hydrolyze before it gives positive result for Benedict’s test.
Iodine test is used to detect the presence of starch in a solution. When starch presents, iodine changes its colour from yellow to dark purple. Benedict’s test is used to detect the presence of reducing sugar in a solution. When reducing sugar presents, a brick-red precipitate appears in the solution. Benedict reagent contains copper (II) ions, which is blue in colour can be reduced to copper (I) ions, which is insoluble brick-red precipitate when reducing sugar is present. Carbohydrate B is more complex than carbohydrate A, because salivary amylase or hydrochloric acid is needed at 37˚C and 95˚C respectively to be hydrolyzed into monomers before it gives positive result for Benedict’s test. In conclusion, solution A contains simple sugar and solution B contains starch. Salivary amylase actives at 37˚C, while hydrochloric acid actives at 95˚C.
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