Question

Laboratory activity

1) 3 testubes A , B and C with 4ml of starch solution

2) 3, A-1, A-2 and A-3 testubes with alfa amylase: testube A-1 is placed in a cold bath, and B-1 in a 37C water bath and C-1 in a boiling bath for 5 min

3) Transfer contents of tube A into ice bath and pour contents of A-1 to tube A, Mix and place tube A back in ice bath. After 10 min add 2 drops of iodine and note color of solution. Repeat the same for B-1 to B and C-1 to C, using instead the 37C water for B and boiling water for C.

4) Rank the tubes from 1 to 3 with 1 being colorless or meaning greatest digestion, and 3 which means least or no digestion. A dark blue soln indicates the presence of starch and partial digestion of starch results in a violet or red colored soln and a colorless soln indicates the complete digestion of the polysaccharide.

Question: provide color of soln and rank
Temperature :Color of Soln : Rank

1. Ice water bath

2. 37C

3. 100C

Answer 1

Alpha amylase is a hydrolase enzyme that hydrolyses the glycosidic linkages in polysaccharides. Starch, a polysaccharide adsorbs iodine in its chains and branchings which gives a deep blue-black colour. If however starch is hydrolysed, the absence of chains or branchings leaves the iodine unadsorbed leaving the solution colourless. Alpha amylase, like any enzyme has an optimum temperature at which its activity or rate of hydrolysis is highest. Going below that temperature results in a lower activity that leads to partial hydrolysis while going to temperatures much higher than the optimum leads to the denaturation of the enzyme thus leaving the starch without hydrolysis.

The enzyme is present in the human body and over the course of time has evolved to be most efficient at the temperature of a human body - 37^oC. Thus, in ice, below the optimum temperature, the enzyme hydrolyses very slowly while at a boiling bath, it gets denatured leaving the starch intact. Therefore, the order of hydrolysis is as 3 < 1 < 2 giving 2 to be colourless, 1 to be violet or red and 3 to be dark blue in colour.

Ice water - violet or red : 2

37^oC - colourless : 1

100^oC - deep blue : 3