|Concepts of Biology (BIOL116) - Dr. S.G. Saupe; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; firstname.lastname@example.org; http://www.employees.csbsju.edu/ssaupe/|
Gink and Go Make Mayonnaise
Setting: Go's kitchen. On the counter is a bottle of vinegar, a bottle of vegetable oil, and an egg. Gink arrives hungry as usual.
Gink: Hey dude .got anything for me to eat?
Go: If you wait just a minute, I'll have some yummy mayonnaise. Hand me the oil and water over on the counter.
Gink: I had hoped for some Ho-Ho's, but I guess mayo will do. Are oil and water ingredients in the mayo?
Go: You bet they are and I'm going to mix them up right now.
Gink: Wait a minute, oil and vinegar don't mix. Remember that oil is hydrophobic and non-polar, but the vinegar is hydrophilic and polar. You can't mix them to make creamy mayo. Look I'll sketch what happens when you mix them together
Go: Right, but I have a secret.
Gink: I hope this isn't one of Saupe's silly tricks.
Go: Nah - I learned it from Harold Morowitz in his essay, "Mayonnaise and the Origin of Life" (Berkley Books, NY, 1985).
Gink: OK, so what's the trick?
Go: You need an egg.
Gink: Oh, I was wondering what that what the egg was for. I thought you were gonna make an egg salad sandwich with it.
Go: No hungry one - we're need the egg yolk. It contains lecithin which is a phospholipid.
Gink: I remember phospholipids from Saupe's biology class - aren't they the molecules made of a 3-carbon glycerol backbone? Two of the carbons are esterified to fatty acids and the other is attached to a phosphate group which is further attached to another charged group (draw one here)
Go: Wow, you amaze sometimes. The molecule then has a two-tailed sperm appearance with the fatty acids representing the tail and the phosphate and charged group begin the head. (sketch one)
Gink: What happens when you put phospholipids in water?
Go: They form a bilayer which is a very stable configuration. The non-polar tails groups are arranged together toward the inside while the polar head groups are oriented to the outside. (Sketch this arrangement)
Gink: Yup, I even remembered that. But what I don't understand is how this will help make mayonnaise.
Go: Simple - the phospholipids form a single layer around the droplets of vegetable oil, emulsifying the mixture. (Sketch this).
Gink: Wow, that's radical. Is that the same as the structure of the oleosomes in the seeds of plants that store oils?
Gink: Let's get to work, I'm starving. But, I still have one question. Why did what does the origin of life have to do with mayonnaise?
Go: Good question. Morowitz suggests that one of the first things that had to happen during the evolution of cells was the formation of the cell membrane - it was necessary to separate the internal cellular environment from the external environment. I like his quote, "From a more humanistic point of view, individuality entered the world when the first membrane fragment wrapped itself into a closed shell and separated the interior components from the rest of the universe."
Gink: So, you're suggesting that over 3.5 billion years ago someone made some mayonnaise and it became alive? Will our mayonnaise creep out of the jar?
Go: Don't be silly. Morowitz is simply saying that phospholipids were probably floating around in the primordial oceans of the earth. These components found there way to small pools along the shoreline and as they evaporated this primordial oil slick of phospholipids would have spontaneously aggregated to form small vesicles - the beginning of simple cells.
Gink: Awesome. It sounds as though this process and these vesicles are similar to liposomes.
Go: You bet. Let's eat!
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