As I grew up, different states of matter were an interesting phenomenon. I would get ice and drop it in water just to watch it melt. Naturally, as a 20-something graduate student, accidentally making something precipitate (crystallize out of solution) in the lab got me to thinking about biological states of matter. I never did figure out why my experiment precipitated, but I DID come up with a lab to do with you!
In each cell, we have proteins that have different jobs, ranging from simply holding other cellular components together, to making the energy we need to survive. When these proteins are made, they are transformed from a single peptide of amino acids, like biological legos,into a folded protein by chaperone proteins. Think of it like parents or teachers overseeing children learning a new project. They help the kids learn how to do things the right way to get the right result. Chaperone proteins help newly formed proteins fold correctly and get the right chemical modifications to do their jobs in the cell.
When we do experiments in a research lab, we often have to collect proteins to study, but we also have to modify them to do our experiments. A common way is to heat the sample of proteins to near-boiling. By treating the proteins like this, we cause a chemical change in the proteins, called denaturation. This means we are breaking the weak hydrogen bonds that held the protein in shape (but NOT the strong, covalent peptide bonds that hold the peptide together) and linearizing the peptide.
Usually, this change is irreversible, so, if the conditions are right, the linearized proteins will not reform their folded shape, but instead tangle up on themselves and precipitate when the solution is cooled.
Today, we are investigating the same type of change in my Bucket Biology Lab, but by other means. When we cook eggs, the egg white goes from runny and clear to solid and white. This is due to the denaturation and coagulation (tangling) of the proteins in the egg white, most of which is a protein called albumin. However, we have cooked an egg in a pan before. Today we will “cook” an egg with alcohol.
Disclaimer: While the result is the same, I can assure you that they are not nearly as tasty as heat-cooked eggs. The author may or may not have tried some egg denatured with ethanol, and the result is not pleasing. PLEASE DO NOT EAT THE DENATURED EGGS as you can get food poisoning, and especially DO NOT EAT THEM IF YOU USE RUBBING ALCOHOL for the experiment, which is a poison.
Small Glass Bowl
An Egg (or more if testing different conditions)
70% Rubbing Alcohol (Isopropanol, or alternatively high-proof ethanol)
- Break the egg into the bowl. You can “scramble” it if you would like, but the end result is not as nice looking.
- Gently pour some alcohol over the egg.
- Swirl gently.
- After 5-10 seconds, you should notice the egg white turning white.
- With 70% isopropanol, maximum coagulation should occur in 15 or so minutes.
How this works:
The proteins in the egg white are in an aqueous solution, one that is water based. Alcohol is an organic solvent, and it disrupts the hydrogen bonds in the proteins it comes into contact with. Because alcohols are organic, they can often also interact with the hydrophilic core of the protein, the part of the protein that does not interact well with water and is usually wrapped inside the middle of the protein, away from the aqueous solution. Thus, like with heat, the alcohol causes the proteins to linearize and then tangle, giving you a “cooked” egg.
Other conditions can also result in precipitated proteins, such as high salt, or highly acidic or alkaline solutions. These types of conditions remove the proteins from their normal environment, making it difficult for them to maintain their structure. Thus, this laboratory would be versatile for both older and younger students with the addition of a range of different solutions and/or different concentrations of solutions.
Which solutions will you test when you do the experiment?
- Build a hypothesis for what will happen when you add alcohol to the egg.
- What did you observe before, during, and 15 minutes after addition of the alcohol to the egg?
- Was your hypothesis correct?
- How do you think the changes observed occurred?
- What other conditions could we try to get a similar result?
Biotechie (Social Media Manager) Biotechie is the Science ACEs social media manger (@scienceaces and facebook.com/scienceaces). She is a rising 3rd year PhD student researching cell fundtion, cholesterol, and obesity. You can follow her personal twitter @biotech_babe.