Skip to main content
Biology LibreTexts

5.4: Proteins

  • Page ID
  • 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.


    Biuret test for Protiens


    • Test tubes
    • Test tube racks
    • Wax pencil
    • Biuret reagent


    Hypothesize about which substance(s) will produce a color change with the Biuret test


    1. Label test-tubes 1 – 6.
    2. Draw a line 1 cm from the bottom of each test tube and another line 2 cm from the bottom of each tube.
    3. Fill in Table 3 to specify which tube will receive which test solution.
    4. Add the appropriate test solution to the level of the 1 cm line.
    5. Add Biuret reagent to the 2 cm line of each tube. Mix gently.
    6. Record data in the table
    Tube Contents Final Color Check if protein present
    1 Distilled water    
    2 Potato Juice    
    3 Glucose    
    4 Milk    
    5 Egg White    
    6 Unknown