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Saturday, January 29, 2011

Membranes: The amazing phospholipids

Phospholipids are amazing molecules.  Place them in a watery environment and they self associate into a spherical ball and make membranes. Membranes made of phospholipids  are fluid structures which are sticky  to themselves, so that they make a barrier which typically defines, in part, the outer boundry of a cell and helps hold things in the cell, yet it remains a fluid.  Life would not work without these fluid barriers.  Who would of thought of that?  What a perfect idea for a membrane, a fluid barrier!  We would be very stiff creations indeed if our membranes were not made out of these soapy molecules. 

So we see in membranes the same principle we discussed regarding the idea that all macro-organisms are made of smaller pieces or entities  we call cells, i.e.,  membranes are made of lots of smaller parts (phospholipids). Relatedly, we also see modularity, i.e., the parts are somewhat interchangeable and  pliable.  And this modularity and pliability allows for a lot of things to be stuck in membranes.

But, if phospholipids are sticky (self associate because of hydrophobicity) why don't all cells near one another, stick together and form one big clump....for instance when we bump into each other  why don't we form one big glumpy smear of phospholipid humanity on the earth.   How do pond organisms swim around with these sticky membranes and not get stuck or fuse together?  In fact this is how some viruses work, they invade cells by fusing their outer lipid membrane envelope  with the cell membrane, and they take advantage of this sticky/hydrophobic effect.  Works like a charm.  The virus fuses to the membrane and releases its contents ( at least some viruses work this way, not all do).

So my questions for this blog are;

1 Why and how do phospholipids self associate?
2 What prevents membranes from fusing with all other nearby membranes?
3 Could the self assembly of phospholipids be a posssible explanation for how the first cell membranes evolved?
4 When phospholipids form membranes in a water based environment, do they make membranes  similar to the cell membranes we find in cells today?


  1. 1. I believe the answer lies in peptides, because this affects the membrane's selectivity to other cells. There are a few factors that determine the peptide sequence, one of which are specific amino acids. The peptide sequence results in the formation of a-helical bundles that make the membrane want to bond strongly to other membranes. Peptides self-associate depending on many factors, some of which include mutations and fatty acids. Sounds complicated!

    2. I did not find a specific answer to this, but I believe the answer could be that membranes do not fuse because of lipids alone, they have to have proteins to make fusion happen. The lipids also have to undergo physical change in order to fuse. When I rub up against something or someone does not mean that my membranes of my cells are undergoing physical change.

    3. Well, for starters, I do not believe cell membranes evolved, I believe they were created by God. However, if I were to take the position of a evolutionist, I would say that if all of the elements needed to make a cell membrane were close together, they would want to be bonded to each other. It would take the right amount of the correct peptides, proteins, phospholipids, etc to make a cell membrane.

    4. Yes, when the phospholipids are in a water based solution, they actually form a bilayer, and arrange themselves so that the hydrophilic heads face out. This allows certain substances to enter the membrane, but keeps most things out.

  2. Micayla, thanks for being the first responder. Your first answer probably won't work as stated....self assembly of pure phospholipids into a membrane would not involve peptides.

  3. This comment has been removed by the author.

  4. I'm not sure about this but i found that most phospholipid layers are made out of non-covalent bonds which because of this, allows it to not stick to other molecules? According to wikipedia, "There are four commonly mentioned types of non-covalent interactions: hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions." Instead of chemically sharing electrons, the bond is made by a "dispersed electromagnetic interactions."

  5. 1) Phospholipids self associate for one reason: to form a bi-layer, hiding their hydrophobic tails from H20 and to associate their hydrophilic polar head group towards the H20.
    Phospholipids are made of a polar head group: a diglyceride, a negatively charged phosphate group, that is attracted to water; and a long chain of fatty acids and hydrocarbon chains, that are hydrophobic (repel water). Because of this amphipathic nature, the hydrophobic tails repel the water and come together while the hydrophilic polar heads line up facing the water. So when the phospholipids are suspended in water, they come together and form different types of membrane structures. But in all cases, the hydrophobic fatty acids are excluded from water and the hydrophilic phosphate sections interact with the water. They can form a sphere which fully encases water in the inside and excludes water on the outside, thus keeping the fatty acids away from the water. The phospholipids can from a couple of different types of membrane types such as the micelle, the liposome, and the bilayer sheet.

    2) To help find the answer for this question, I looked up some instances when cells do fuse. Like in fertilization, embryogenesis, and viruses. According to Wikipedia, fusion takes place because of the interplay of various interfacial forces, like hydration repulsion, hydrophobic attraction, van der Waals forces, and even sometimes mediated by proteins.
    When two hydrated bilayers experience a strong repulsion as they approach one another. This is hydration repulsion ( hydration repulsion- the work required in removing the water molecules around the hydrophilic molecules in the bilayer system. The water molecules are attracted to the hydrophilic head groups and try to arrange themselves around the head groups and it becomes very hard to separate this attraction. So because of hydration repulsion, it could conceivable be to much energy to separate the H2O molecules form the polar head groups, thus preventing them from sticking and merging.
    But adhesion between the phospholipids do not follow the same principles as the fusion between two membranes. In order for cells to adhere to one another, Cell Adhesion Molecules are required. CAMs are proteins that are located on the cell membrane surface involved with binding to other cells. They are transmembrane receptors that are hydrolyzed (a chemical reaction in which molecules of water are split into hydrogen anions) by extracellular enzymes. But cell-cell adhesion in eukaryotes are mediated by cadherins which basically allows cells or disallows cells to adhere together and make junctions. In prokaryotes, the cell-cell adhesion is are formed by molecules called “adhesins” that bind them together. Adhesion between viruses and host cells occur because they also have adhesion molecules that help them bind to host cells.
    So basically my investigation led me to this… cell fusions do not take place randomly, there are forces that keep them apart (usually). Cell adhesion also does not take place randomly. The cells have adhesion molecules that regulate what they adhere to.

  6. 3) I would say not. A bunch of phospholipids could not just evolve together at the same rate and become a complex bi-layer membrane. Where would these complex phospholipids come from? They would have to be created by something. So let’s say that they were synthesized. But then that would mean a cell would be already there with DNA. But how would this cell be protected? It wouldn’t be, that would mean that even before the cell was able to evolve a membrane, it would die because their would be no container holding all of the organelles. I do not believe this is a possible explanation for how cell membranes evolved.

    4) As I stated in question 1, they can from many different kinds of membrane structures like the micelle, the liposome, and the bi-layer sheet. The micelle is a spherical shaped phospholipid chain with only 1 layer essentially it has a single sheet of polar heads facing the water while the tails all congregate towards the center of the sphere. The liposome is an interesting concept. It is also spherical in shape, but it is sphere with an empty middle (think of a jelly donut with the jelly missing). The polar heads face outward again for the outside attracted to the water with its hydrophobic tails pointing towards the center again, but the center is actually hollow, with a second layer of phospholipids, this time the heads are facing towards the center forming a hollow section. The tails meet up with the first layer’s tails, thus protecting them from the water. Lastly the bi-layer sheet is the one we are most familiar with, it is a thin sheet of 2 layers of phospholipids that connect together forming a continuous sheet that stretches into a spherical shape.
    One thing in common with these 3 different types of phospholipid formations is that they all seem to form spheres, which makes sense because it is the only way to form a continuous barrier that protects the hydrophobic tails.

  7. 1: When the phospholipids are near one another, the can adjust their mechanical properties-meaning that they resist stretching and bending. The adjustment of temperature can also effect how they associate with themselves. At low temperatures, the bilayer can ‘adopt a solid gel phase state but undergo phase transition to a fluid state at higher temperatures’.
    Im having a hard time coming up with an answer for that question so that’s all I have so far.
    2: I think that by the inner layer of the phospholipid being hydrophobic, phospholipids can clump together but will never fuse into each other’s membranes because it’s against their nature.
    3: I don’t really think that cell membranes evolved but I do think that with changing conditions, evolution does occur with cells, and really any living thing over a long period of time. Evolution- meaning change. Organisms adapt to their conditions so therefore change must occur. Cell membranes created by phospholipids are easy to create. They are created by mixing lipids with water, and some sort of electrolyte solution that contain salts. However, these membranes aren’t just composed of lipids, but they also contain proteins. I think that the structure of the cell membrane can change depending on the condition, or in this case the ingredients of what’s available to create the cell membrane.
    4: I would say yes because cell membranes that are in the cells of humans are created in a mostly water based environment, so I would say that they are most likely similar to phospholipids that form membranes in a water based environment also. The structure may be a little different because of the amount of salt content, and other things that are in the water which contribute to the formation of the membrane as well. Different kinds of proteins could also be in the water so depending on what resources are available all depend on the similarity of cell membranes that are formed from the phospholipids.

  8. 1. Why and how do phospholipids self associate?
    Phospholipids could self associate because of their Amphipathic character. The Phosphorus head is hydrophilic while the fatty acid chain is hydrophobic. Naturally the hydrophilic end of the phospholipid will be attracted to water and the hydrophobic end to another phospholipid through non-covalent bonds. This forms the bilayer that is seen in many membranes.

    2. What prevents membranes from fusing with all other nearby membranes?
    After some research, it would seem that Cell Adhesion Molecules regulate when cell membranes can fuse together. Also, some of these CAMs are Calcium-dependent, which could be related to the smooth ER which regulates the concentration of Calcium ions. Maybe the smooth ER releases some Calcium ions when the cell needs its membrane to fuse?

  9. 3. Could the self assembly of phospholipids be a possible explanation for how the first cell membranes evolved?
    Probably not. Because a large amount of phospholipids would have needed to evolve at the same time and in the right conformation in order to form the attraction that we see in plasma membranes. The only way all of these factors could have come together is through a design. One could say that the cell itself could have designed it’s own membrane, but how could a cell function without a membrane to begin with? It’s organelles would be floating around and it’s DNA would be scattered. This reminds me of Friday’s class when Dr. Francis showed us the picture of a ruptured bacterium. It’s DNA was scattered outside of the cell, along with other essential cellular components. The only way phospholipids could form a bilayer is through an external intelligent source. (The creator God)

    4. When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today?
    Phospholipids naturally form a bilayer in a water based environment. Because the hydrophilic phosphate head naturally attracts water while the hydrophobic fatty acid opposes water. The hydrophobic ends are protected from water by the hydrophilic ends which form on the outside, next to the water. This forms a membrane that is similar to the cell membranes that we find today.

  10. I'm loving everyone's comments! Very encouraging!

  11. 1. Phospholipids definitely associate because the attractive forces between them are greater than those from the surrounding environment. 2.It's possible that phospholipids in the cell membranes do not fuse with the cell membranes of other cells due to the proteins interspersed in them.
    3. One of the problems with phospholipids resulting in the evolution of a cell is that one would have to ask why the self association does not continue until all the phopholipids are one mass. Before it is a cell, it may not have any proteins in it and may easily interact with other phospholipids, supposing this is an uncontrolled process. However, that is not the case.
    4. In a basic sense, I would say they do.

  12. 1) I agree with Erik. Phospholipids have polar heads and nonpolar tales. The tales naturally don't want to be touching water, thus the bilayer configuration.What i would find interesting is whether this would still happen if you placed phospholipids in a non polar solution( although i would guess that this would just result in the bilayer flipping around) My point is this: do the phospholipids self-congregate, or is the water pushing them together?
    2)Cell membranes don't stick to each other, because they are always surrounded by water. The attraction between the water molecules and the membranes is so great that the membranes never actually get to touch, so their is no opportunity for fusion. also, it seems like the parts of the membranes that would touch are both polar, therefore the molecules would have one positive and one negative side. if the membranes were coming together, they would be opposites of each other, therefore the parts of the molecules that would need to touch would have the same charge, forcing them apart. maybe that's why special molecules are needed for two separate membranes to fuse together.i don't know if that makes sense....
    3)If you were a biologist that was desperate to make the theory of macroevolution work, i could see how the evolution of the cell from a random ball of phopholipids would make sense. there are a lot of problems with that idea, however. where did the organelles inside the cell come from? how did they(in some cases) become surrounded by a membrane too? how did proteins come to be interspersed throughout the membrane? and most importantly, how does something that isn't alive adapt to its surroundings? molecules and atoms don't develop, so it makes no sense that they would evolve.
    4)they are similar in one sense. phopholipids do freely associate into a bilayer because of their amphipathicity. however, they are not exactly like the ones in cells, because cell membranes don't just have phospholipids, they also have have all kinds of proteins and cholesterol interspersed in them to give them a structure.

  13. 1) Why and how do phospholipids self-associate?

    Phospholipids self-associate by the hydrophobic effect. Once connected, the associated phospholipids create a membrane which both retains necessary fluid like the cytoplasm and repels substances that could harm the cell.

    2) What prevents membranes from fusing with all other nearby membranes?

    According to Faraday Discuss., 1999, 111, 55-68, “Previous studies from this laboratory have shown that the enzymic generation of diacylglycerol in bilayers by phospholipase C may lead to membrane fusion through the formation of transient non-lamellar lipidic intermediates.” For membranes to fuse, there must be some substance formed and at work in the membranes to cause fusion. If the substance, diaglycerol for example, is not present, membranes will not fuse.

    Also, “Lipid bilayer fusion is thought to involve formation of a local hemifusion connection, referred to as a fusion stalk. The subsequent fusion stages leading to the opening of a fusion pore remain unknown. The earliest fusion pore could represent a bilayer connection between the membranes and could be formed directly from the stalk. ” Biophys J. 2002 November; 83(5): 2634–2651. If the formation of a fusion stalk and fusion pore could be prevented by the cell unless specifically triggered, then perhaps non-intentional lipid bilayer fusion could be prevented (like people sticking together).

  14. 3) Could the self assembly of phospholipids be a possible explanation for how the first cell membranes evolved?

    At first glance, it seems that the association of phospholipids could explain the origin of cell membranes. However -- and perhaps I am over-simplifying -- this doesn’t make sense. How does a cell survive without any sort of membrane? The membrane would have had to have been present at the beginning of the cell’s existence and developed to the point where it could contain and protect the contents of the cell.

    4) When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today?

    Yes. Looking back to the first part of the blog, “Place [phospholipids] in a watery environment and they self associate into a spherical ball and make membranes.” The membranes that are formed are bilayers, just like cell membranes.

  15. Phospholipids are able to self associate because they are amphipathic molecules. For instance the hydrophobic regions aggregate together along with the hydrophilic regions. The hydrophobic regions which “fear water” associate side-by-side and inverted to create a bilayer. Thus the phospholipid bilayer.

    The membranes do not fuse with themselves and collapse because the cell contains a cytoskeleton which maintains the general shape of the cell and the pressure of the fluid in the cell would also prevent it from collapsing on itself. Why they don’t associate with other phospholipid bilayers is another story. It doesn’t seem to me that these would fuse with other cells. The hydrophobic regions on the phospholipids fuse together because they area inside and outside the cell are made of mostly water so they naturally seek water opposing molecules like themselves. The hydrophilic regions do not have any need to fuse with other cells though because they are “water loving” and since they are already surrounded by water, have no desire to merge with other membranes. Viruses are able to fuse with membranes but use a protein to fuse with cells.

    I believe that hypothetically this is true but cell membranes are a lot more than simply phospholipids which self aggregate. Membranes consist of cholesterol and many proteins and it was not just happenstance that these membranes arose because they have a perfect assembly of these other macromolecules. I would say then that it is highly improbable that phospholipids ability to form by individually gave rise to the first membrane.

    Yes, these molecules are able to assemble by themselves to create a barrier in a natural environment.

  16. 1. I was seeing that phospholipids covalently bond and so we put near each other I would guess that they are attracted to each other like a Sodium atom would be attracted to a Chlorine atom so the bond is hard to break. Unlike the NaCl molecule though the phospholipid biayer actually comes closer together when put in water. The head of the phospholipid which is toward the outside is hydrophilic so it enjoys being in the water. I'm not sure this is correct but that could explain the attraction of phospholipids to each other and then it forms a phospholipid bilayer because the hydrophobic tails of the phospholipids bind with each other and form a bilayer where the inside is hydrophobic and the outside is hydrophilic.
    2. I read in here ( that the phospholipid head which is a phosphate group is polar so I would guess that the phosphates of another membrane cannot fuse with this membrane because they are not attracted to each other so just like 2 magnets of the same polarization they would repel each other before the other membrane could even get close enough to be sticky and stick to it.
    3. I agree with Sam that you would need a cell membrane there so it could not have evolved it would have had to be there from the very first cell. We even saw with that bacteria from last week that when it was put into water that was off balance in salt content the cell burst and without the cell membrane in tact the DNA spilled everywhere and if the cell were not created I could not think of a way that the cell membrane would just happen to form around that amount of DNA and package it up all nice and pretty like it is seen in cells.
    4. Yes I would think they would because the hydrophobic region of the phospholipids would automatically bind with each other and as more came the process would keep going till they were all together and the hydrophobic ends were attached to each other and the hydrophilic ends were facing the water which would in turn form a phospholipid bilayer.

  17. To answer the first question, I got the idea from a few different things I read that the reason that the phospholipids associate the way they do is due to the hydrophobic nature of the tail and the hydrophobic nature of the head. It's like oil only one end of the molecule is hydrophilic so that end of the bilayer is always pointed outward since cells contain allot of water.

    To answer the second question, it seams like the would not be attracted due to the polarization of the molecule. Since the inside of the bilayer is hydrophobic it would repel the outside of another bilayer.

    After looking around a little, it seams that most evolutionist don't even believe that the original cells had a phospholipid bilayer membrane but rather a "simpler" membrane just made up of nucleic acids since phospholipids are synthesized by cells and don't just happen outside of cells. So that doesn't really work.

    Do they form membranes in water? I would think so for the same reason they do in water, because they have the one hydrophobic end, those ends would be attracted to each other.

  18. Greetings to my especially smart peers!! The question that interested me the most was #2 about why the membranes do not stick together. All I could guess was the fact that cells are always maybe the "friction" between the membranes would cause them to not stick together? Well, since I knew my prediction was wrong, I looked up the answer on google. :) I found out that the large amount of Cholesterol in the membrane has a lot to do with it! pretty cool website. :D

  19. 2) I think cell's plasma membrane contains enzyme and membrane channels that play the role of signaling to the cell. These proteins and receptors inform the cell to yield and response to other cell and necessary molecular around them. This process is similar to how cell react to stimuli to prevent other cells fuse to it.

  20. 1. The reason that phospholipids associate in water has to do with their hydrophobic and hydrophilic ends. Their nonpolar heads are attracted to eachother and are mutually repulsed by water.
    2. A component of membranes that could stop them from fusing to all other membranes could be the proteins interspersed throughout the membrane that recognize cell membranes of the same organism, but don't allow cohesion between different the membranes of different creatures.
    3. Trick question? They didn't evolve. From the evolutionists point of view however, it seems that phospholipids are capable of self associating in water, so it seems like they could be able to do this on their own.
    4. A major difference between a group of phospholipids and a cell membrane would be the proteins inside the membrane. They would be similar in that they don't allow ions or water through, but the structural and functional differences because of the lack of membrane proteins would be huge.

  21. As I went back and reviewed everyone's comments, I realized that I was way off for question 1. The general make up of phospholipids would make them associate in water, because of their hydrophilic and hydrophobic ends, as has already been said. Nice work everyone!

  22. For the first one, as everyone has said, it has to do with the phospholipids being amphipathic meaning they are both hydrophilic and hydrophobic. Their hydrophobic sides will form together and the hydrophilic the same and create the bilayer protecting the cell from unwanted substances.
    The second one is because of the cells cytoskeleton, which keeps the cells main shape also allowing the cell to move wherever it is needed and protecting the organelles inside of the cell.
    The third one, I agree with Susan and Sam-a-lama. Without a membrane telling it to come together and tell it what’s good and bad, there is not way it would randomly happen to form around random matter that just happened to make a membrane.
    In that way stated, I would say yes.

  23. Most likely my answers will look very similar to other people’s answers, but this is what I have found.
    Phospholipids associate based on their two parts: their tail and their head. The head is hydrophilic and the two tails are hydrophobic. When the membrane is placed in water the tails orient themselves toward the center which means the center of the membrane contains almost no water.
    Membrane fusion does occur, but these reactions are catalyzed by proteins. If the right proteins are not present, the membranes will not fuse. In an article describing membrane fusion from the Max-Planck-Institute for Biophysical Chemistry it says, “These proteins mediate the initial recognition of the membranes that are destined for fusion and pull the membranes close together to destabilize the lipid/water interface and to initiate mixing of the lipids.” Sometimes only one protein is required, but other times actual complexes are required. Without these entities fusion is not going to occur; however sticky the membrane might be.
    This question does not make too much sense to me. I think it was Sam that said the membrane had to exist simultaneously with the cell, there could not be a cell without a membrane and I agree with that. The cell could not have existed without the membrane, it would have fallen apart so if evolution was involved, they would have had to evolve at the same time which would require everything to be placed in exactly the right spot; which is highly unlikely.
    Yes, they do. It is the water that forces the phospholipids to form the bi-layer because it forces the hydrophobic tails inward.

  24. 1.) Phospholipids organize themsleves into bilayers in water because of their polarity. The tails want to be away from water and the heads are attracted to it.
    2.) Certain transmembrane proteins must be present for membranes to fuse. Water constatnly surrounds lipid membranes and the attraction to water molecules keeps them from sticking to other membranes. But when the right enzymens and proteins are present in the membrane, they allow it to fuse with other membranes.
    3.) I guess you could say that meybe some phospholipids globbed together in a membrane trapping some random elements and amino and nucleic acids inside which formed proteins and some genetic material and poof you have a cell...
    4.) No, random "membrane" formation in water doesn't really resemble a cell because it doesn't have the supportive cytoskeleton that cells do, which give it some stability and shape.

  25. 1. Phospholipids self associate because of their amphipathatic state, being hydrophilic and phydrophobic. I think this allows them to change their state allowing them to resist being suctioned in with another phospholipid.
    2. I think phospholipids help along with other minerals like proteins to allow the membranes not to fuse together.
    3. I do not believe that cell membranes evolved. I believe things probably changed within the phospholipid membrane. I believe over time they gathered information from probably the simplest phospholipid bilayer and became more complex over time.
    4. I think that the phospholipids do form a cell membrane when injected in water that are similar to the ones we have today because I think the water kind of forces them together creating the membrane.

  26. 1) The heads of the lipid are electrically attracted to each other because they are hydrophilic and their tails repell water by hydrophobic affect. Therefore they force to form a double layers to have this amphipathic effect.
    2)Could it be the proteins on the membrane preventing the cells to fuse together? There was an experiment by Larry Frye and Michael Edidin about fusing human cell with mouse cell and they did fuse together. But the hybrid cell dies after a brief period of time.

  27. 1 Why and how do phospholipids self associate?
    according to the Pubmed website, the hydrophic affect plays a big role in the self association there is something that takes places that allows them to resist the suction which keeps things out leading to the thus the self association!
    2 What prevents membranes from fusing with all other nearby membranes? It should be the proteins however there is more going on here, " Like all fusing bilayers, viral envelopes locally adopt hourglass-shaped stalks during the initial stages of fusion, a process that requires local negative membrane curvature. Unlike cellular vesicles, however, viral envelopes do not redistribute lipids between leaflets, can only use the energy released by virion proteins, and fuse to the extracellular leaflets of cell membranes. Enrichment in phospholipids with hydrophilic heads larger than their hydrophobic tails in the convex outer leaflet of vesicles favors positive curvature, therefore increasing the activation energy barrier for fusion. Such phospholipids can increase the activation barrier beyond the energy provided by virion proteins, thereby inhibiting viral fusion." (pubmed)
    3 Could the self assembly of phospholipids be a posssible explanation for how the first cell membranes evolved? they could trap certain things within which could lead to taking shape in a cell eventually i am not completely sure about this one!
    4 When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today? cholesterol seems to be envolved however water is more active in this process pushing the cells and fluids together!!

  28. If cells were to stick together just because of touching each other then the main system of our bodies would shut down. The thickness that is full of mass doesn't move very good gets stuck easy this is what would happen if phospholipids didn't self accosiate.

  29. also another thought is that if they are self accosiating because there are others that are sticky and would try to break into the membrane in order to damage it perhaps, thus it is a protective barriers as well!!

  30. Phospholipids self-associate because they have both hydrophobic and hydrophilic ends. When placed in water, the hydrophobic ends congregate together in an effort to get as far away from the water as possible leaving the hydrophilic tails in the water.
    One reason why membranes do not fuse together when next to each other could be that the tails of the phospholipids form the outside of the membrane. These tails are hydrophilic and want to be in water not in another membrane.
    I guess an evolutionist could use self-association as a way to explain membranes however as creationist we know this is not true because God created membranes. Also it’s a stretch to assume that all the parts needed for this process to be carried out would evolve at the same time or be able to subsist for long periods of time unfinished until all the parts evolved over millions of years.
    Yes they do. They associate like they do in a membrane with the hydrophobic heads congregating together and the hydrophilic tails facing out.

  31. 1. Phospholipids self-associate due to either the hydrophobicity of the N-terminus or the C-terminus, or the peptide sequence by specific amino acids. This results in forming a-helical bundles that bind to certain membranes, this in turn forms strong hydrophobic bonds.

    2. I'm not entirely sure, but I'm guessing that membranes require certain proteins to tell it to fuse to certain things but not to others. Therefore, without these proteins, it doesn't fuse with other membranes.

  32. Phospholipids self associate because they are ampiphatic. The head is hydrophilic and the end is hydrophobic. These two properties form the phospholipid bilayer.

    In order to fuse with one another, there would have to be attraction. There could be receptors that interact with only select molecules. The proteins in the bilyer could also aid in preventing the fusion of the membrane.

  33. 1 Why and how do phospholipids self associate?

    they associate to for a double phospholipid layer called a bilayer this layer is used by the cell to protect the cell and to allow certain things in and certain things out of the cell membrane.

    2 What prevents membranes from fusing with all other nearby membranes?

    the phosphate group is polar (hydrophilic),and the other is The fatty acid tails are nonpolar (hydrophobic)so they can't bind due to the fact that they are of different poles so they do not attract to one another. there is also proteins on the outside of the bilayer that don't allow anything to bind to the bilayer as well.

    3 Could the self assembly of phospholipids be a posssible explanation for how the first cell membranes evolved?

    possible, then if we consented to this then why don't we just aggree with evolution! i thing that these were specificly created for there certain purpose and that is why they exists they could possible belive that they could have divided more and branched off into more of them but not totally sold on the idea yet.

    4 When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today?

    When phospholipids are exposed to water, they set themselves into a bi-layered sheet with all of their tails pointing toward the center of the sheet. so i am not sure if this is the same as the cell membranes that we see today though.but if they forn in water then they possible will be similar to those that we see today.

  34. 1. Why and how to phospholipids self associate?
    The existence of lipid asymmetry in membranes depends on the very slow rate at which individual phospholipids can “flip-flop” — spontaneously move from one monolayer to the other. The bilayer can adopt a solid gel phase state at lower temperatures but undergo phase transition to a fluid state at higher temperatures. The reason these phospholipids self associate is because it is responding to its environment,and they respond according to their polarity.

    2 What prevents membranes from fusing with all other nearby membranes?
    The outer heads of the membrane are hydrophilic and the inner part is hydrophobic meaning that they connect to one another based on their polarity. To me, this would be related to magnets and the reason these hydrophilic heads do not stick to one another is because other membranes are composed of the same hydrophilic head meaning the same polarity. Like "charges" in do not attract.

    3 Could the self assembly of phospholipids be a posssible explanation for how the first cell membranes evolved?
    This could possibly be an explanation in the sense that over time cells will adapt to their external environment meaning that these membranes are forming to protect the cell and create an almost impenetrable barrier.

    4 When phospholipids form membranes in a water based environment, do they make membranes similar to the cell membranes we find in cells today?
    I would say yes because don't all cells need a fluid/water based environment to survive? The cells would self associate with each other and stick together to then form the membrane.

  35. 1 Phospholipids self associate to form a membrane because they are sticky and are hydrophobic. Since they are hydrophobic they all come together and form by attaching to one another.
    2 The fact that phospholipids are semi permeable prevents it from fusing with all other nearby membranes. Semi permeable means it only allows certain things to pass through. This prevents any unwanted thing in and also prevents fusing with unwanted things. Another reason is that the membrane is both hydrophobic and hydrophilic this is due to the phospholipid bilayer. This bilayer is hydrophophobic on the outside and hydrophilic on the inside.
    3 This could be possible because the way phospholipids come together seems basic and then it gets complex. So there can be some building ground there. There is no other good explanation for how the first cell membranes evolved. Another thing going for the phospholipids is that is assembles by itself and nothing else is needed. This may indicate that it’s the original way membranes came to be.
    4 Yes they do form similar cell membranes we find in cells today. They both have the same phospholipid bilayer and same structure. There is not much difference between them. The water based environment causes the bilayer to go inside out with the hydrophilic side on the outside.

  36. 1. Natural bilayers are usually made mostly of phospholipids, which have a hydrophilic head and two hydrophobic tails. When exposed to water, they arrange themselves into a two-layered sheet with all of their tails pointing toward the center of the sheet. The hydrophobic tails resist the water, causing them to align themselves in this fashion.
    2. Once the membranes are joined, the hydrophilic heads are not attracted to other heads. Because water molecules are attracted to the hydrophilic heads, it forms a layer of water around the cell that probably hinders the joining of two separate cells. The cells are usually coated by other substances, like carbohydrates, which could create buffers between cells. Cells walls and envelopes could also act as “buffers” between cells.
    3. In terms of evolutionary theory, absolutely. But the key problem is that a cell is way more complex than a simple bilayer membrane. A lot of things in nature happen because of natural forces—different forces attract or repel each other, but there is no proof that simple attractions between phospholipids are able to produce anything more complex than an empty membrane.
    4. In basic structure they are similar, but the water based membranes lack many of the complexities necessary in cell membranes. Phospholipid membranes are impermeable to water soluble molecules, which is why in cells the membranes are imbedded with thousands of proteins.

  37. (1)Phospholipids are built on phosphoglycerides. Due to phosphoglyceride membrane having an additional group linked to the phosphate, choline, choline is what causes the phospholipids to self-associate. Since choline is small and hydrophilic, and together with the negatively charged phosphate to which it is attached, this begins the process of self-association of the phospholipid.
    I think that phosophlipids self-associate because due to their nature of containing both hydrophilic and hydrophobic regions.
    (4) Yes because most cell membranes are made of phospholipids. Phospholipids construct the structure of membranes by hydrophilic phosphate region interacting with water, and hydrophobic fatty acid regions excluding from water.

  38. 1.Phospholipids self-associate because they are amphipathic, meaning one part is hydrophobic and the other part is hydrophilic. The hydrophobic and hydrophilic parts are attracted to each other and therefore the strand of lipid bilayer is forced to come together like a ring, thus forming the membrane. This article section explains it well: “The formation of micellar and vesicular structures (and monolayers, too) is the consequence of the hydrophobic effect. The large hydrocarbon tails aggregate in the center of the particle excluding water from contact with the non-polar structures (dielectric constant D=2). The charged, polar headgroups form the particle's surface making it perfectly soluble in water (dielectric constant D=80).”

    2.I was reading about viral fusion and a mechanism called Arb that works to inhibit the viral membrane from fusing to the host cell’s membrane. I’m not sure the details of intercellular interaction, but it would make sense if a similar mechanism is used to prevent cell-cell fusion. Maybe there is a protein within the membrane, or an enzyme that blocks cell-cell fusion or something that can detect when a cell is close and somehow prevent cell-cell fusion based on that detection.

    3.I think it would be difficult to support the idea of self-assembly as evidence for evolution, because phospholipids naturally come together based on polarity and their interaction with water. I wouldn’t know how to support what came before the process of phospholipids coming together to form membranes. There was no in-between stage, thus the continuing problem for evolutionists: “the search for the missing link”. Also, the cell wouldn’t have been able to survive prior to the cell membrane formation, the organelles and DNA would not be contained. If any critical part of a cell is missing, it does not function therefore evolution can’t make sense.

    4.Yes, because the polar heads that interact with water curl together so the hydrophobic tails face away from the water and towards each other. It is because of the polarity of water-based conditions that phospholipids form the bi-layer membrane structure.

  39. 1 Why and how do phospholipids self associate?
    i am tempted to answer "magic", but that is not it. Could it be because they recognize "like-bodies"? are they attracted because of their characteristics in water? it is almost like they attract each other like magnets do, they are able to find each other because of their hydrophilic and hydrophobic characteristics, and then a membrane is created.

    2 What prevents membranes from fusing with all other nearby membranes?
    its almost as if, once the phospholipids form a membrane, its there, and it isn't going to join with others. I know that this is not a legitimate theory though, because the membranes can break apart. the bond created is difficult to break, and we don't just morph with everything else becoming a massive blob. this is not like the tag game "amoeba." even the fact that the heads of the phospholipids repel each other would help cells from morphing together all the time.

    3 Could the self assembly of phospholipids be a possible explanation for how the first cell membranes evolved?
    i guess that evolutionists could use this as a viable argument for evolution itself. The fact that the phospholipids attract each other would definitely help, however, i believe there is still a problem here: how could they develop this characteristic? where did the second one come from? where did enough phospholipids appear to even create a full-blown membrane. it would be possible for them to "self-create" a membrane once all the phospholipids were there.

    4 When phospholipids form membranes in a water based environment, do they make membranes  similar to the cell membranes we find in cells today?
    yes, the water causes them to come together because of their characteristics in water.

  40. I have a question, I'm not an expert in the area but I know a bit. Once I heard that membrane phospholipids in the exoplasmatic face can "fuse" with the ones on the citosolic face, causing the membrane to be a monolayer.

    Can this happen? If it can, why and what does it cause in membrane properties?

  41. Javier,

    Good question. Membranes in cells do fuse naturally with one another under certain cell processes like endocytosis and exocytosis and lysomosomal fusing etc....however it is my understanding that the end result of these fusions is the bilayer membrane, there may be some intermediates which are monolayer for a short time, but this is not the stable conformation of membranes in cells as I understand it. Also, fusogenic substances like the divalent cation calcium can cause distortions in membranes and most likely monolayer configurations but again, this is probably short lived.