L9: PROTEIN IDENTIFICATION

1. INTRODUCTION

Biuret's test is a chemical test used for detecting the presence of peptide bonds. A peptide bond can be broken by hydrolysis (the adding of water). In organisms, protein molecules called enzymes facilate the process.

The biuret reaction can be used to assess the concentracion of proteins because peptide bonds occur with the same frequency of amino acid peptide. 

The solution to be tested in treated with a strong base followed by a few with a strong based followed by a few drops of copper (II) sulphate. If the solution turns purple, protein is present.

2. OBJECTIVES

- Identify peptide bonds.

- Compare protein concentracion in differents foods.

3.MATERIAL

- 7 x 250mL beaker

- 6 test tubes

- Test tube rack

- 6 x 10mL Pipet

- Mortar

- Glass marking pen

- Gloves

- Goggles

- Milk

- Soy milk

- Egg

- Yogurt 

- Potato

- Distilled water

- NaOH 20%

- 10 drops of CuSO4

4. PROCEDURE

First of all are going to dilute the protein,

1. Add 100mL of distilled water to each 250mL beaker. Label them with M (milk), S (soy milk) and EW ( egg white), EY (yolk), Y (yogurt) and P (potato).

2. Separate the egg white nd the yolk in another beaker.

3. Smash the potato in a mortar and add some amount of the smashed potato to the P beaker.

Prepare the samples:

4. Add 10 mL of a dispersion of each food ( M,S,EY,EW and Y) to the indicate beaker. Calculate the final concentracion. All the groups will use the same dispersion from the beakers.

5. Prepare 6 test tubes and label M,S,EW,EY,Y and P. Add 2 mL to test tube of the every food disolution of each beaker.

6. Add 2 mL of 20% NaOH dissolution.

7. Shake gently and add 5 drops of CuCO4 in each tube. Allow the mixture to stand for 5 minutes.

8. Note any colour change. Remember that proteins will turn solution pink or purple.

9. Compare the test tubes.

5. OBSERVATIONS

6. QUESTIONS

1. Which food has protein? 

Animal food.

2. Which food has more proteins? Why?

Eggs white, yogurt, potato and milk. Are animal food.

3. Do you find any different between soy and cow milk?

Rice milk, doesn't have protein, however has milk has.

4. Is there any different among milk and yogurt?Why?

Yes. Yogurt has more protein than milk.