Name(s): ______Period: ______Group: ______

Lab:DENATURING PROTEINS—Group 1
Objective:To experiment with different methods of denaturing the protein found in
egg white (albumin) and milk (casein)
Background:
Proteins are large molecules made up of small amino acids. Proteins are held in a natural
shape due to the interaction of side groups on the amino acids from one part of the
molecule to another area of the molecule. These interactions may be hydrogen bonds or
disulfide bonds. We can denature the proteins by disrupting the H-bonds that are within
the structure. When this happens the overall shape of the protein changes and new
properties can be observed. The shape of a protein is associated with food processing
properties, such as solubility, gel formation, and enzyme activity.
PROTEIN DENATURATION or WHAT HAPPENS WHEN YOU FRY AN EGG?
In the egg whites the albumin will change from clear to white. We will explore how the
following denature egg albumin as well as milk casein.When egg white is heated above a certain temperature (i.e. 60 °C) bonds in the protein moleculesbreak and reform in different ways. This causes the protein molecules to denature or lose theircharacteristic three-dimensional structure. As the proteins uncoil, they tend to interact with eachother to form a solid mass or coagulum (the process called coagulation). This explains the changesthat we observe as we watch an egg being cooked. However, factors other than high temperaturemay also produce this denaturationphenomenon.
  • Heat – done by cooking
  • Acids & bases – can form ions on some side groups of amino acids
  • Organic compounds – form their own hydrogen bonds with the amino acids
  • Heavy metals – react with disulfide bonds
Procedures for Denaturation Labs:
Group 1 -Denaturation by HEAT
Materials
1 glass dish
1 paper cup
1 set of measuring spoons
1 test tube in test tube rack
1 egg
2 –50 ml beakers of milk (15 ml each)
50 ml beaker of Lemon juice (5 ml)
Stirring rod
Egg Albumin Procedure:
  1. Separate 1 egg white, placing the egg whites in a large glass dish. Discard the egg yolk into the paper cup.
Note: The clarity of the egg white this is your baseline or control, record your observations in Data Table 1 below.
  1. Transfer approximately 15ml (1 tablespoon) of egg white into 1 test tube for heating.
  2. Take the test tube to your instructor to be placed in boiling water and allowed to “cook” till egg turns white.
  3. Record your observation in the Egg Albumin Data Table (Data Table 1) below , and for Group 1 and on the front board.
  4. Now Do Milk (Casein) Denaturation.
Procedure for Milk (Casein) Denaturation:
  1. Pour the 5 ml of Lemon juice into one of the beakers of milk and stir.
  2. Compare the beaker with lemon juice and milk to the beaker with only milk. Look for any changes in color, texture, etc…
  3. Record Observations in Data Table 2 on page 3, and on the front board next to your group number.
DATA TABLE 1~ Egg Albumin Data Table
Group / Added / Observations
ALL GROUPS / Nothing—initial observation
1 / Heat
2 / NaCl – Ionic Compound (heavy metal)
3 / NaHCO3– Base
4 / Lemon Juice – Acid
5 / Rubbing Alcohol – Organic Liquid
6 / Pine Apple Juice- Acid
DATA TABLE 2~ Milk Casein Data Table
Group / Added / Observations
Your group / Lemon Juice – Acid
Other groups / Lemon Juice – Acid
Post Lab Questions:
1.Copy and record all the Data on the front board into your data tables.
2. What three factors have caused denaturation of the egg albumin in this lab?
3. What common result occurred in all of the experiments with the egg albumin?
4. What results did you get with the milk casein?
5. Was the milk casein denatured?
6. Did all of the groups get the same results with the milk casein? If not list the differences.
7. Explain the changes that you observed in terms of change in protein structure at the
molecularlevel (be very specific). You may want to get a copy of an article called
‘Denaturation’ from your instructor to help you answer this question.

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