Coacervates Lab

Coacervates are a life-like creation that prove that life may have formed from simple organic substances under the right conditions that eventually led to the formation of prokaryotes. Sometimes called protocells, these coacervates mimic life by creating vacuoles and movement. All it takes to create these coacervates is protein, carbohydrates, and an adjusted pH. This is easily done in the lab and then the coacervates can be studied under a microscope to observe their life-like properties.

Materials:

• goggles
• lab coats or protective covering for clothes
• compound light microscope
• microscope slides
• coverslips
• test tube rack
• small culture tubes (one tube per student)
• rubber stopper or cap that fits the culture tube
• one medicine dropper per tube
• 0.1M HCl solution
• pH paper
• coacervate mix

Making the coacervate mix:

Mix 5 parts of 1% gelatin solution with 3 parts 1% gum acacia solution on the day of the lab (the 1% solutions can be made up ahead of time). Gelatin can be purchased at either the grocery store or a science supply company. Gum acacia is very affordable and can be bought from some science supply companies.

Procedure:

1. Put on the goggles and lab coats for safety. There is acid used in this lab, so extra precautions should be taken when working with the chemicals.
2. Use good lab practices when setting up the microscope. Make sure the microscope slide and coverslip are clean and ready for use.
3. Obtain a clean culture tube and a test tube rack to hold it. Fill up the culture tube about half way with the coacervate mix which is a combination of 5 parts gelatin (a protein) to 3 parts gum acacia (a carbohydrate).
4. Use a dropper to put a drop of the mix onto a piece of pH paper and record the initial pH.
5. Add a drop of acid to the tube and then cover the end of the tube with a rubber stopper (or culture tube cap) and invert the entire tube once to mix. If this is done properly, it will turn somewhat cloudy. If the cloudiness disappears, add another drop of acid and invert the tube once again to mix. Continue adding drops of acid until the cloudiness stays. Most likely, this will not take more than 3 drops. If it takes more than that, check to be sure you have the right concentration of acid. When it stays cloudy, check the pH by putting a drop on pH paper and record the pH.
6. Place a drop of the cloudy coacervate mix on a slide. Cover the mix with a coverslip, and search under low power for your sample. It should look like clear, round bubbles with smaller bubbles inside. If you are having trouble finding your coacervates, try adjusting the light of the microscope.
7. Switch the microscope to high power. Draw a typical coacervate.
8. Add three more drops of acid, one at a time, inverting the tube to mix after each single drop. Take a drop of the new mix and test its pH by putting it on the pH paper.
9. After washing your original coacervates off of your microscope slide (and the coverslip, too), put a drop of the new mix on the slide and cover with the coverslip.
10. Find a new coacervate on low power of your microscope, then switch to high power and draw it on your paper.
11. Be careful with clean up of this lab. Follow all safety procedures for working with acid when cleaning.

Critical Thinking Questions:

1. Compare and contrast the materials you used in this lab to create coacervates to the supposed materials available on the ancient Earth.
2. At what pH did the coacervate droplets form? What does this tell you about the acidity of the ancient oceans (if it is assumed this is how life formed)?
3. What happened to the coacervates after you added the extra drops of acid? Hypothesize how you could get the original coacervates to come back into your solution.
4. Is there a way coacervates may be more visible when looking through a microscope? Create a controlled experiment to test your hypothesis.

Lab adapted from original procedure by the University of Indiana