Experiment 3 – Testing for proteins Proteins are complex molecules often with a

Question

Experiment 3 – Testing for proteins

Proteins are complex molecules often with a 3 dimensional structure. These biomolecules are composed of amino acids building blocks joined by peptide bonds. Proteins form structural components of cells, insulin, hemoglobin, muscle, enzymes, eye, hair color, and thousands of other essential body components. Proteins can be identified using the Biuret test. In the presence of peptide bonds, Biuret reagent turns from blue to purple.                 

Materials

Biuret Solution

Unknown solution

Knox gelatin

1% glucose solution

5 test tubes

10 ml graduated cylinder

100 ml graduated cylinder

Pipettes

Spatula

Thermometer

Marker / wax pencil

2 beakers

* distilled water

* hot water

* egg white

* you must provide

Procedure

1. Label five test tubes 1 – 5

2. Prepare samples as follows:

a. In a 250 ml beaker mix the packet of knox gelatin with 50 ml hot water, and stir until dissolved. Place 5 ml of this solution into test tube 1 using a clean graduated pipette.   

b. In a separate 250 ml beaker, mix the white from one egg with 25 ml water to create an albumin solution. Place 5 ml of this solution into test tube 1 using a graduated pipette.

3. Place 5 ml 1% glucose solution into test tube 3.

4. Place 5 ml water into test tube 4.

5. Place 5 ml unknown solution into test tube 5.

6. Record the initial color of each sample in table 3.

7. Add 5 drops of Biurets solution to each test tube. Swirl each tube to mix.

8. Record and color change in table 3.

   Note: If a light purple color is observed, protein is present in the sample.

Table 3: Experimental Results for Testing for Protein

Sample

Initial Color

Final Color

Positive for protein (yes or no)

1 – gelatin

2 – albumin
     (egg white)

3 – glucose

4 – water

5 - unknown

Table 3: Experimental Results for Testing for Protein

Sample

Initial Color

Final Color

Positive for protein (yes or no)

1 – gelatin

2 – albumin
     (egg white)

3 – glucose

4 – water

5 - unknown

Explanation / Answer

Table:3 Sample initial color final color positive for protein (yes or no) Gelatin blue purple yes Albumin blue purple yes Glucose blue no color change no Water blue no color change no Unknown blue If and only if it contains protein it gives purple color ctherwise no color change

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