cell membrane - (Dec/28/2006 )
On my book, it says Cell membrane consists of two layers of lipid molecules. Protein molecules are embedded in this lipid bilayer. My question is: What is on the inner memberane surface and outer membrane surface. i think lipid molecules are on the both surfaces because of the first sentence i wrote, but on my book, it says, the protein molecules may be on the inner membrane surface, on the outer membrane surface, or may extend entirely through both membrane surfaces. so i am totally confused, i don't know where the protein molecules should be on?! Also, my teacher told us that 'P L L P' which means protein molecules are on the two surfaces, lipid molecules are between.
Hope you can give me idea, i am just so confused! Thanks so much!
I attempted to answer your question but more I write more confusing it will be for U. It is best to refer to some figure of cell membrane. It will make U clear.
Here's a link http://personal.tmlp.com/Jimr57/textbook/c...r3/chapter3.htm
This site gives U the description in the simplest possible way with lot of animations to help U understand. If still U have confusion, please post your question again.
the membrane consists of two layers of phospholipids (amphipathic molecules, mainly hydrophobic, with a hydrophilic head), the outer surface is hydrophilic, and the inner part of the membrane is hydrophobic.
some proteins contain hydrophobic domains, called transmembrane domain, and this domain will be in the lipidic membrane. proteins can be exposed to the outer surface or the inner surface. the domain that is exposed to the surface is hydrophilic.
Hope you can give me idea, i am just so confused! Thanks so much!
If I remember right the fluid mosaic model was established in 1972; there was that proposed what your books says; in the mean time, it seems to be as missele says: membrane proteins are integral and mostly have cytoplasmic and extracellular domains; some such as calmodulin or PKC may transiently bind to lipids f.i. to phosphatidylserine which coactivates some PKC; transient binding is useful for translocation and regulation;
some proteins can be lipidated, mostly palmitoylated upon signaling pathway activation, so the protein will be anchored via the lipid moiety to the lipidic membrane.
Here is a picture for the structure of cell membrane. As you can see the picture, the two surfaces are phospholipid.!! the protein just travels around. THey just appear like a point, not the whole surface. i think the two surfaces must be lipids, and proteins are just like some points stand out. What i mean is that proteins don't cover the whole surface as lipids shown above do. THat's my point. I really don't understand how come it would be 'P LL P' , it should be 'L pp L'.
I'll try not to muddy the waters further. Your teacher told you "PLLP" as a way of memorising the membrane structure. He may have been talking about the orientation of the phospholipid. The phosphotidyl group (P) of the phospholipid head (the circle) is hydrophillic so is in the aqueous layers i.e. on the internal and external surfaces. The lipid tails (L) (the two lines) are hydrophobic and will be inside the bilayer so you get "PLLP". Proteins can be membrane spanning which will have extracellular and intracellular domains with a hydrophobic transmembrane domain in the membrane. Other protein may be external or internal with or without transmembrane (they sometimes have anchors which insert into the membrane see farnesyl groups or GPI anchors)
http://www.bbc.co.uk/education/asguru/biol...ane/index.shtml has another diagram if you need one.
The membrane is a fluid layer like the surface of water with proteins "swimming" in it either above and below the surface or just above or below.
Hope that helps (?).
Ceri