L9. PROTEIN IDENTIFICATION

L9. Prtoein identification

1. Introduction

Biuret's test is a chemical test used for detecting the presence of peptide blond's. Polypeptids as protein, are chains of amino acids links togerther by peptide bonds.

A peptide bond can be broken by hydrolysis. In organisms, protein molecules called enzymes facilitate the process.
The solution to be tested in treated with a strong base followed by a few drops of copper(II) sulphate.

Only peptids with a chain of at least 3 amino acids give a significant measurable colour shift with these reagents. Protein in the alkaline environment reduce Cu2+ to Cu+, which forms a coordination complex with protein, leading to a blue to pink-purpule colour change.


2. Objectives

• Identify peptide bonds
• Compare protein concentration in different foods.

3. Hypotesis

the hypotesis is getting to identify food that contains protein and not.

4. Material

• 7x250mL
• 6 test tubes
• test tube rack
• 6x10mL pipet
• mortar
• glass marking pen
• gloves
• goggles
• milk
• rice milk
• egg
• yogurt
• potatoe
• distilled water
• NaOH 20%
• 10 drops of CuSO4

5. Procedure

We are going to determine protein concentration in some foods: milk, rice milk, yogurt, potatoe and egg. We are going to test separately the egg white and the yolk.

First of all we are going to dilute the protein. We add 100mL of ditillated water to each 250 mL beaker. Label them with M(milk),R(rice milk),EW(egg white),EY(yolk), Y(yogurt) and P(potato).

After, we separate the egg white and the yolk in another beaker and smash the potatoe in a mortar and add some amount of the smashed potato to the P beaker.

Now we prepare the samples:

First of all, we add 10mL of dispersion of each food(M,R,EY,EW and Y) to the indicate beaker. Calculate the final concentration. All the groups will use the same dispersion from the beaker.

After, we prepare 6 test tubes and label M,R,EW,EY,Y and P. Add 2mL of the every food dilution of each beaker.

We add 2mL of 20%NaOH dissolution and shake gently and add 5 drops of CuS in each tube. Allow the mixture to stand for 5 minutes. 

Finally, we note any colour change. Remember that proteins will turn solution pink or purrple. Compare the test tubes.

6. Observations

To dilute the food we like food you contain protein canvian color, and react with a stronger or less lilac, segons the amount of protein they contain.

7. Conclusions

Has arrived at the conclusion that food animals are you contain a high level of proteins, such as egg white, milk, yogurt, potato.

8. Questions

1. Which food has protein?

Egg white, milk, yogurt, potato, utimately, the animal food.

2. Which food has more protein? why?

1st - Egg white, 2n- yogurt, 3rd- cow milk. Because the animal food is rich in protain.

3. Do you find any difference between rice and cow milk?

Rice milk dosen't have protain however cow milk does.

4. Is there any difference among milk and yogurt? why?

Yes, yogurt has more protain than milk.