Name:
Date:
.
The Chemistry of Scrambling Eggs
What type of changes occur when you cook an egg?
The major protein in egg whites are
.
Proteins are large molecules made up of a sequence (or sequences) of
Proteins are held together by
side groups on the amino acids interact.
and
.
bonds that form when the
What happens to these bonds when proteins are exposed to extreme heat?
This process is called protein
.
How can we observe that this has occurred?
Other changes that can cause protein denaturation are the addition of:




Acids or Bases
Salts
Heavy Metals
Organic Solvents
Now we will do an experiment to actually see how these conditions cause protein denaturation.
You can work in groups of two. Closed-toe shoes and safety glass are required!
This is what you will need for this lab:
100 mL liquid egg whites
Test Tube Holders
Bunsen burner
9 test tubes
Ring stand
15 mL salt solution
Stir rod
15 mL 1M sodium hydroxide (NaOH)
2 400 mL beakers
15 mL 3M hydrochloric acid (HCl)
Test Tube Rack
15 mL 0.1M copper(II) sulfate (CuSO4)
Ice
15 mL rubbing alcohol (isopropanol)
Procedure:
Part I
1. Place 300 mL of water in a 400 mL beaker, place on ring stand and heat to boiling.
2. Fill another 400 mL beakers ¾ full of ice.
3. Label 6 test tubes #1-7.
4. Transfer egg white in each test tube until ¼ full.
5. Place test tube #1 in the boiling water (carefully) and allow to “cook”. Note observations.
6. Place test tube #2 in the beaker full of ice for 1 minute. Note observations (If any).
7. Add 50 drops of NaCl solution to test tube #3 and stir. Watch carefully and note observations.
8. Add 50 drops of 1M NaOH to test tube #4 and stir. Let the reaction sit for 1 min, note
observations.
9. Add 50 drops of 3M HCl (Carefully!) to test tube #5 and stir. Note observations.
10. Add 20 drops of 0.1M CuSO4 to test tube #6 and stir. Note observations.
11. Add 50 drops of 70% isopropanol to test tube #7 and stir. Note observations.
Test
Tube
1
Condition
High Temperature
2
Low Temperature
3
With Salt
4
With Base
5
With Acid
6
With Heavy
Metal
7
With Organic
Solvent
Observation






Increased Temperature – Increasing the temperature increases the kinetic energy of
molecules, which causes the hydrogen bonds to break and the protein to denature.
Decreased Temperature - A decrease in temperature stabilizes protein structure as it
decreases kinetic energy. Therefore, proteins are often stored by freezing them.
Adding Salt - An increase in salinity can denature proteins. The ions from the salt bind
to certain amino acids and disrupt the ionic bonds in proteins.
Acids & Bases – Each protein is functional within a specific pH range. Above and
below this pH range the protein denatures and the protein loses activity.
Organic Compounds – form their own hydrogen bonds with the amino acids, which
disrupts the hydrogen bonds within the protein.
Heavy metals – Heavy metals such as lead, mercury and cadmium denature proteins by
binding with sulfur groups. This disrupts the disulfide bonds that form in certain amino
acids of proteins, and cause the protein to denature.
Now that you have a better idea of protein denaturation, design your own experiment using the
provided materials. Before testing your conditions, think about what you believe will occur and
write it in the expectation section below. Then, test your conditions and write what you actually
observed.
PART II
Test Tube
1
Condition
Expectation
Observation
2
Questions
1. Which method appeared to have the most dramatic denaturing effect? Why do you think this
method had a greater effect?
2. Why is milk (high in protein) given to someone who accidentally ingests a heavy metal ion
such as silver or mercury?
3. Why are heat and alcohol used to disinfect medical equipment?
4. Which of these conditions does your body use to digest proteins in food?
Adapted From:
University of Nebraska-Lincoln, Food Science Labs, submitted by Deb Dommel
http://www.math.unl.edu/~jump/Center1/Labs/DenaturingProteins.pdf
Aidan Sterk’s Digital Portfolio, protein denaturation lab
https://sites.google.com/a/hightechhigh.org/aidan-sterk-s-digital-portfolio/home/10th-grade/10thgrade-chemistry-and-math/chemistry-labs/protein-denaturation-lab