Expert: Profile Closed - 10/4/2009

Question
QUESTION: I am making trying to make a biphospholipd membrane, you suggested me to use jello like layer right? I was wondering if I can make a jello then put it in a blender so that it will be almost be liquid, but won't mix with other liquids. My teacher and my friend suggested me not to use that method, but they didn't tell me why. Can you tell me the cons behind my method? And whether should I use soft jello or hard jello for this.

ANSWER: Hi, thanks for the question.

The reason that you probably shouldn't go with the "liquidy" jello is primarily that you're relying on the integrity of the set jello to prevent mixing; jello that's liquid enough to move would mix completely after about 12 hours, and you wouldn't get the nice different layers. Again, you have to remember that, because we're not on a cellular level, you're having to set up a system with force enough to prevent the natural tendency of a layered system collapsing.

Remember that a real phospholipid membrane isn't liquid anyway, so making your model from something like jello would be more accurate. It's also worth planning how you're going to represent the bilayer structure; remember that the top and bottom layers of the membrane contain the same materials (hydrophobic ends) so it should really be just a two-color model - two identical jellos at the top and bottom representing the hydrophobic areas, and a different colour in the middle for the hydrophilic.

You might also want to accompany your layered structure with models (made from Lego or similar) showing how the molecules making up the membrane fit together. You could also demonstrate hydrophobic interactions with water and oil in a glass.

Hope this helps; I have more info regarding the way we conduct this practical, so if there are any points you want more detail on, don't hesitate to let me know.
Thanks again, best wishes.


---------- FOLLOW-UP ----------

QUESTION: I am thinking of creating the whole structure (phospholipid, protein cholesterol) using flour dough since I can mould it easily. Is there any problem that might occur? Also I want to ask if I should make hard jello (more gellitone) or soft ones.

ANSWER: Salt-based flour dough should work ok as a modelling agent provided it's not in contact with liquids. And we usually just make the jello using the amount recommended by the manufacturer on the packet; sometimes, with the cheaper jellies, you have to add a bit more to make it set firm. In any case, err on the side of making it too firm, not too sloppy. This'll stop the colours running and ruining the separation. Hope this helps!





---------- FOLLOW-UP ----------

QUESTION: What is err???? What are salt based flour dough?? (never heard of the term) Is it ok if I cover the dough with a layer of oil?? does that help?

Answer
Hi, and thanks for the follow-up

Err as in "commit an error";
http://www.merriam-webster.com/dictionary/err

I just meant it's better to make the jelly too thick rather than too thin, so if in doubt, add more jello to your mix.

Salt-dough is a mix of flour and salt that can be shaped and baked; it's better than other doughs because it sets rock-hard, and the salt helps to preserve it. 2 cups of plain flour, one of salt and one of water. Put in a bowl and knead until mixed, then use to make your model. Bake in an oven till set (about half an hour). You probably won't need to cover it in oil, but it depends exactly what you want the model to do.

If you have them available, you may find something like lego or wood a better modelling material for a simple system like a bilayer; the dough works but is a bit of a fuss when you're only trying to provide a visual guide.

Hope this helps, best wishes.