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Course Code: SBI4U: Biochemistry
Teacher Demo: Denaturing Proteins
Topics
protein
denaturation
acid
Timing
preparation: 10-20 min
demonstration: 5-10 min
Specific Expectations: SBI4U
Introduction
Proteins have specific uses inside cells to support biochemical reactions important for cell
structures and metabolic processes. Cells maintain a balanced internal environment that allows
these proteins to retain the structure important to whatever action it performs. In this demo, the
impact of an acidic environment is used to denature albumin, the protein in egg white. It can be
used as a starting point for a discussion of protein biochemistry such as the way that proteins are
dependent on their structure for function and once that structure is disturbed, proteins usually no
longer function properly.
This demonstration is best used with students who have some understanding of protein structure
(primary, secondary and tertiary).
Materials
one raw egg (white only)
100 mL distilled water in 250 mL Erlenmeyer flask
10mL of 0.1 mol/L hydrochloric acid
one dropper/pipette bottle
one pair vinyl (or nitrile) gloves
one pair splash goggles
Safety Considerations
Hydrochloric acid (HCl) is corrosive to skin and eyes.
Wear gloves and splash goggles and do not inhale fumes.
Be aware that some people are allergic to egg proteins.
An alternative to egg white is a protein solution made from protein powder.
Procedure
Preparation
1. Add egg white to flask of distilled water.
2. Swirl gently to make an egg white solution.
3. Transfer 10mL 0.1mol/L HCl to dropper bottle. Label clearly.
Predict/Explain
4. Organize students into pairs for this demonstration. Ask them to record their thoughts.
5. Hold up the flask of egg white solution and the dropper bottle of hydrochloric acid.
6. Explain that you will be adding an acid solution to this solution.
7. Ask students to predict what they think will happen and explain their thoughts.
Observe
8. Ask each pair to describe the egg white solution in the flask.
9. Walk around the class so that people can make their observations.
10. Place 10 drops 0.1M HCl into flask.
11. Swirl flask until precipitate is formed.
12. Ask students to describe what they observe.
Explain
13. Instruct the student pairs to review their prediction.
14. Ask students to share their notes and list possible reasons for this change.
Disposal
Neutralize the egg white solution with a base (e.g. baking soda solution). Discard the precipitated
egg white in the garbage and pour remaining fluid into municipal water system.
What happens?
Albumin is a globular protein that can be mixed with water. The hydronium ions (H3O+)
resulting from the strong acid (HCl) disrupt the structure of this globular protein so that it
denatures (unravels/unfolds). As a result, the egg white becomes opaque white and is no longer
mixed with the water. It will then settle to the bottom of the flask.
How does it work?
Protein function is dependent on protein structure. Protein molecules are usually very long
chains of amino acid building blocks that must fold in a certain way to achieve the shape
required for function. Anything that changes the shape of a folded protein has the potential to
disrupt the protein’s function. Adding a strong acid to the egg white changes the shape of the
egg’s proteins (the most abundant of which in the egg white is albumin) and makes the proteins
non-functional. This is called denaturation. The egg white becomes opaque because the
changing shape of the proteins changes their optical properties so that the egg white is no longer
transparent to light. Denatured proteins cannot be refolded into their correct shape (called
conformation) and thus cannot be made functional again.
Teaching Suggestions/Hints
1. Ensure to swirl gently when making egg white solution. Vigorous shaking may denature
the protein before the demonstration.
2. This demo can be used to demonstrate how changes to protein structure affect the
protein’s ability to function.
3. This demo can be used to generate ideas with respect to the structural changes made by
disruption to different functional groups.
4. When considering specialized organelles, this can generate a discussion about the
necessity of isolating low pH in the lysosome to activate the lysosome enzymes without
denaturing other enzymes in the cell.
Next Steps
1. This demo can lead into the role of active sites and allosteric sites of various enzymes.
The role of the allosteric site allows a cell to temporarily disrupt a protein with
denaturing it entirely.
2. Students can be asked to research denaturation further and develop an inquiry to
investigate their literature research.
Additional Resources
1. A YouTube video of this demo performed with three different acids:
http://www.youtube.com/watch?v=DedE68fjKRM
2. An excellent intro to proteins: http://grade9chem.weebly.com/proteins.html
3. More detailed info on protein denaturing agents:
http://www.elmhurst.edu/~chm/vchembook/568denaturation.html
Specific Expectations
SBI4U
A1.1 formulate relevant scientific questions about observed relationships, ideas, problems, or
issues, make informed predictions, and/or formulate educated hypotheses to focus inquiries
or research
B3.2 describe the structure of important biochemical compounds, including carbohydrates,
proteins, lipids, and nucleic acids, and explain their function within cells
B3.4 describe the chemical structures and mechanisms of various enzymes