Macromolecule Lab - Proteins and Starches

Summary

This video script outlines a lab experiment to test for proteins, starch, and sugar using various reagents. It details the materials needed, the procedure for testing substances like milk, egg whites, and sucrose solutions with Biuret and Iodine reagents, and how to record results in tables. The script also prompts viewers to hypothesize, record observations, and draw conclusions about the presence of these macromolecules.

Takeaways

• 🔬 **Materials Needed**: Test tube rack, test tubes, transfer pipet, protective glasses, paper bags, DI water, various solutions, and reagents like Biuret, Iodine, and Benedict's are required for the experiments.
• 🧪 **Protein Testing Protocol**: To test for proteins, add 3ml of the substance to a test tube, add 5 drops of Biuret reagent, mix, and observe the color change.
• 📊 **Results Table**: Create a results table labeled 'Table 1' to record the contents of each test tube and the final color after adding Biuret reagent.
• 💧 **DI Water as Negative Control**: DI water is used as a negative control in the protein test and is expected to remain blue, indicating no protein presence.
• 🥛 **Milk and Egg White Positive Results**: Milk solution and 50% egg white solution turn pinkish-purple, indicating a positive test for protein.
• 🍬 **Sucrose Negative Result**: 1% sucrose solution remains light blue, indicating a negative test for protein.
• 🌟 **Observing Color Changes**: The color change after adding Biuret reagent is crucial for determining the presence of protein.
• 📝 **Conclusion Section**: After recording results, analyze whether they were expected and explain any unexpected outcomes, suggesting next steps.
• 🍠 **Starch Testing Protocol**: Similar to protein testing, but uses Iodine reagent, with positive results turning purple to dark-purple/ black.
• 🥔 **Starch Results**: 1% starch solution turns light purple, indicating a positive test for starch, while other substances tested negative.
• 🤔 **Unexpected Results Analysis**: If results are unexpected, consider possible reasons and what steps to take next, such as retesting with fresh materials.

Q & A

What is the purpose of the experiments being performed?

The experiments are designed to test for the presence of organic macromolecules such as proteins, starch, sugar, and fat using various reagents.

What materials are required to perform the experiments?

The materials needed include a test tube rack, 4-5 test tubes, a transfer pipet, protective glasses, 3 pieces of paper bag, DI water, evaporated milk, 50% egg white solution, 1% sucrose solution, 1% starch solution, onion juice, 10% sucrose solution, vegetable oil, Biuret reagent, iodine, and Benedict's reagent.

How do you perform the test for proteins?

To test for proteins, 3ml of the substance is added to a test tube using a transfer pipet. Then, 5 drops of Biuret reagent are added, the mixture is swirled, and the color change is observed. A blue color indicates a negative result, while a purple or pinkish-purple color indicates a positive result for protein.

Why is DI water used in the protein test?

DI water is used as a negative control in the protein test. Since water should not contain proteins, it is expected to show a negative result (blue color) when Biuret reagent is added.

What were the results of the protein test for each substance?

Test tube 1 (DI water): blue, negative for protein. Test tube 2 (milk solution): pinkish purple, positive for protein. Test tube 3 (50% egg white solution): purple, positive for protein. Test tube 4 (1% sucrose solution): light blue, negative for protein.

What reagent is used to test for starch and what indicates a positive result?

Iodine is used to test for starch. A positive result is indicated by a purple to dark-purple/black color, while a negative result will remain yellowish-brown.

What were the results of the starch test for each substance?

Test tube 1 (DI water): light yellow, negative for starch. Test tube 2 (1% starch solution): light purple, positive for starch. Test tube 3 (onion juice): light yellow, negative for starch. Test tube 4 (1% sucrose solution): light yellow, negative for starch.

What should you do if the DI water tests positive for protein in the experiment?

If DI water tests positive for protein, it would be an unexpected result. The experiment should be restarted with fresh equipment, reagent, and water samples to ensure accuracy, as DI water is the negative control and should not contain proteins.

Why is it important to include a control in experiments like these?

A control is important because it provides a baseline for comparison. In this case, DI water is used as a negative control to ensure the reagents are working properly. If the control produces unexpected results, it signals that the experiment may have been compromised.

What are the key questions to answer in the conclusion section for each test?

The conclusion section should answer the following questions: 1. What were the results (color changes)? 2. Were the results expected? Why or why not? 3. If unexpected, explain possible reasons and outline what steps would be taken going forward.