Before anyone asks, yes, I did take Olivia Netwon Johns' "Let's get Physical" and give it a scientific application (it was one of my ways of remembering lipid arrangements.
So we know that lipids are amphiphilic (meaning that they have both a hydrophobic head, and hydrophilic tail, or on occasion the other way around). Either way, due to the hydrophobic effect (which as we were told last week, should more aptly be called the hydrophilic effect, as water loves water more) the lipids aggregate themselves into different types of arrangements so as to decrease the overall energy of the system. These arrangements include:
* micelles - like a soccer ball, where each of the hexagons making up the ball have a tail attached, which exists inside the ball (except replace the hexagon with the hydrophilic head)
* bilayer - the classic arrangement we've all been taught for cell membranes, where there are two layers of lipids which come together to create a semipermeable layer.
* vesicle - like a fusion of a micelle and a bilayer. There is the micelles structure, with then what we can consider a reverse micelle within the micelle, interacting with the micelle in the same way that the two layers of the bilayer interact.
Associated with the micelles is a term known as the critical micelle concentration. This term, the CMC, refers to the point where the concentration of lipids is high enough to spontaneously form structures such as a micelle.
Matt, you said "meaning that they have both a hydrophobic head, and hydrophilic tail, or on occasion the other way around". Can you give an example where it is the other way around? I was under the impression that the tail was a tail because it was a hydrophobic hydrocarbon tail, and the head was a localised charged ion, or polyatomic ion, which would be small, like a head. I can't imagine a molecue with a hydrophobic head and a hydrophilic tail.
ReplyDeleteAlso, is there any difference between a liposome and a vesicle? Or are they different terms for the same thing?
Compositionally they are the same thing, but liposomes are artificially made whereas vesicles are 'naturally' made within cells.
ReplyDeleteOk, so Heather has already answered one of those answers for me. In regards to your question about an example of a reverse micelle, I'm not actually able to remember an example on the spot, and I haven't been able to find my old phys chem notes, but I do recall having taught about their existance, where their existance comes about because their tails have hydrophilic properties about them, or have charged groups across the tail which are attracted to water, while the head has hydrophobic properties to them
ReplyDelete