Question

I’ve given you four solutions, in test tubes 1 through 5, and told you that one contains lactose, one contains raffinose, one contains insulin, one contains some extract from a starchy root vegetable, and one contains distilled water. You don’t know what’s in each test tube. I perform the following tests on the tubes and report the following observations.

1. When Lugols reagent is added to tube 4 the contents quickly turn black. This happens in no other tubes.
2. I perform acid hydrolysis reactions on all of the tubes and find that the hydrolysis produces monomers used to build a more complex molecule in all tubes except tubes 1 and 3.
3. Tube 1 tests positive in the Benedicts test. Following hydrolysis, tubes 4 and 5 also test positive in the Benedicts test.
4. Test tube 2 tests positive in the Biurets test before hydrolysis but negative/very weakly positive after hydrolysis.
   
   Based on the data reported fill in the following table. There may not be one single correct answer. You must supply ALL the evidence from the data that supports your conclusion of the contents of a tube. The evidence does not have to be conclusive; it just has to support your conclusion of what is in the tube. A different piece of evidence might be conclusive of what is in the tube. Include even negative evidence (e.g. if a test is negative).
   

Tube	Contents	Explanation
1
2
3
4
5

Answer 1

Tube 1: content: lactose. Explanation: it test positive in the Benedict test. Lactose contains a sugar with a free reducing aldehyde moiety. The Benedict test is used to detect the reducing sugars which contains free reducing aldehyde moiety.

Tube 2: content: insulin. Explanation: this test tube test positive in the biuret's test before hydrolysis. This test is used to detect the presence of peptide bonds. It gives violet colour for proteins and the intensity is in proportion to the number of peptide bonds. Insulin is a protein enzyme.

Tube 3: content: distilled water. Explanation: because acid hydrolysis give no reaction with this test tube. It happens when the test tube contains a blank solution like distilled water.

Tube 4: content: extract of starchy root vegetable. Explanation: lugol's reagent turns it into black. Lugol's solution (elemental iodine solution) stains the starches in organic compound due to iodine's interaction with the coiled polysaccharide structure.

Tube 5: content: raffinose. Explanation: because it tests positive for Benedict's test after hydrolysis. raffinose can be hydrolysed to sucrose and galactose. Galactose contains free reducing aldehyde moiety.