Lab Report: Detection of Proteins using Biuret Solution

Abstract

This laboratory experiment aimed to determine the presence of protein in various samples using Biuret solution. Biuret solution, containing copper ions, undergoes a color change when it reacts with peptide bonds in proteins. The color change from blue to violet indicates the presence of proteins in the sample. Different solutions, including albumin, gelatin, glucose, water, and an unknown solution, were tested for the presence of proteins. The initial and final colors were recorded, and the results were analyzed to determine protein presence.

Introduction

Proteins play a crucial role in our bodies, serving as building blocks for various cellular functions. Detecting the presence of proteins in food or other substances is important for understanding their nutritional value. Biuret solution, containing copper ions, forms a complex with peptide bonds in proteins, leading to a color change from blue to violet. In this experiment, we utilized Biuret solution to test different solutions for the presence of proteins and recorded the color changes to draw conclusions about their protein content.

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Materials and Methods

Materials:

• (2) 250 mL Beakers
• 25 Drops Biuret Solution, H₂NC(O)NHC(O)NH
• (1) Knox® Gelatin Packet
• 5 mL 1% Glucose Solution, C₆H₁₂O₆
• (1) 10 mL Graduated Cylinder
• (1) 100 mL Graduated Cylinder
• Permanent Marker
• 5 Pipettes
• 5 Test Tubes (Plastic)
• Test Tube Rack
• 5 mL Unknown Solution
• Tap Water*
• Hot Water*
• Egg White*

*You Must Provide

Procedure:

1. Label five test tubes as 1, 2, 3, 4, and 5.
2. Prepare testing samples as follows:
   • a. Mix one egg white with 25 mL of water in a 250 mL beaker to create an albumin solution. Pipette 5 mL of this solution into Test Tube 1.
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   • b. Mix the packet of Knox® gelatin with 50 mL of hot water in a second 250 mL beaker. Stir until dissolved. Pipette 5 mL of this solution into Test Tube 2.
   • c. Pipette 5 mL of the 1% glucose solution into Test Tube 3.
   • d. Use the 10 mL graduated cylinder to measure and pour 5 mL of water into Test Tube 4.
   • e. Pipette 5 mL of the "Unknown Solution" into Test Tube 5.
3. Record the initial color of each sample in Table 1.
4. Develop a hypothesis regarding the color change when Biuret solution is added to Tubes 1 - 4. Record your hypothesis in the Post-Lab Question section.
5. Pipette five drops of Biuret solution into each test tube (1 - 5). Swirl each tube to mix.
6. Record the final color in Table 1.

Note: Protein is present in the sample if a light purple color is observed.

Results

Table 1

Discussion

The results of this experiment demonstrated the presence or absence of proteins in different solutions based on the color change observed after adding Biuret solution. The initial and final colors of each sample were recorded in Table 1.

Post-Lab Questions

1. Hypothesis: 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.
2. Molecular Composition: 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.
3. Diet and Nutrition: 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?
4. Other Biomolecule Detection: 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 react 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, producing an orange-red colored precipitate. Alternatively, iodine-potassium iodide (IKI) may also be used when working with starch. IKI contains special tri-iodine ions that 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.
   

Conclusion

This laboratory experiment successfully utilized Biuret solution to detect the presence of proteins in various solutions. The color changes observed in the test tubes indicated the presence or absence of proteins. The results were consistent with our hypotheses and the known properties of Biuret solution. This method can be valuable in nutritional and biochemical studies to determine the protein content of different substances.

Recommendations

Further experiments can explore the quantification of protein concentration in solutions using Biuret solution, providing more detailed information about protein content. Additionally, the application of other reagents, such as Benedict's reagent and iodine-potassium iodide, can be investigated for the detection of different biomolecules.