Experiment 1: Testing for Proteins Data Tables Table 1: Testing for Proteins Res

Question

Experiment 1: Testing for Proteins

Data Tables

Table 1: Testing for Proteins Results

Sample

Initial Color

Final Color

Is Protein Present?

1. Albumin Solution

2. Gelatin Solution

3. Glucose

4. Water

5. Unknown

Post-Lab Questions

Record your hypothesis about what will happen when Biuret solution is mixed with the solutions from test tubes 1, 2, 3, and 4 here. Be sure to use scientific reasoning to support your hypothesis.

Write a statement to explain the molecular composition of the unknown solution based on the results obtained during testing with the Biuret solution and each sample solution.

Diet and nutrition are closely linked to the study of biomolecules. How should you monitor your food intake to ensure the cells in your body have the materials necessary to function?

There are other types of reagents used to determine what type of biomolecule a substance is. For example, copper ions present in Benedict’s reagent reacts with the free end of any reducing sugars, such as glucose, when heated. Originally blue in color, these copper ions are reduced by the sugar, and produce an orange-red colored precipitate. Alternatively, iodine-potassium iodide (IKI) may also be used when working with starch. IKI contains special tri-iodine ions which interact with the coiled structure of a starch polymer. Prior to a reaction, the IKI displays a yellow-brown color; however, after reacting with starch, a dark purple or black color is presented.

The molecule pictured below produced a blue color when tested with Benedict’s reagent, a yellow color when tested with IKI, and a violet color when tested with Biuret reagent. Based on the structure shown below and these chemical results, what kind of biomolecule is this?

Sample

Initial Color

Final Color

Is Protein Present?

1. Albumin Solution

2. Gelatin Solution

3. Glucose

4. Water

5. Unknown

Explanation / Answer

Biuret test is done for protein detection. It specifically detect the presence of peptide bonds in proteins. The reagent is potassium sodium tartrate treated with cupric sulfate and sodium hydroxide in an aqueous solution. The colour of reagent is blue in absence of protein. Cu2+ ions form a violet coloured coordination complex with Nitrogen of peptide bond and oxygen of water.

Albumin is a protein and will give positive biuret test results by showing violet colour when the reagent is added.

Gelatin is also a protein formed from collagen denaturation and contains peptide bonds. It will also give positive biuret test result.

Glucose is a carbohydrate and will give negative biuret test result and water will also give negative results.

Our food should have a balance of carbohydrates ,proteins and vitamins and minerals. Carbohydrates like glucose serve as energy source as their breakdown produces ATP. Proteins act as a source of amino acids which can serve as precursors of cells self synthesized protein molecules. Vitamins and minerals serve as cofactor for various enzymes involved in plethora of cellular processes.

The structure of the molecule is not attached with the question. However from the test results it seems the molecule is protein.

If it was a reducing sugar , it would have given brick red precipitate on reaction with benedict reagent, but it give blue colur which is colour of the reagent itself suggesting no reaction has taken place.

If it was starch it would have given blue-black colouration on reaction with IKI.

It gives violet colour with biuret reagent which is a positive result for proteins

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