Talk:Lipid bilayer

Ye olde comments

What cellular structure is composed of a lipid bilayer?

All cell membrane's consist of a lipid bilayer. It is not so explicit in the article, but it should be. --Lexor 01:55, 21 Sep 2003 (UTC)

Should this article be merged together with other similar structures to "lipid aggregates"? --Eleassar777 15:07, 24 May 2005 (UTC)

I think it should not Karol 15:30, May 24, 2005 (UTC)

Why not? Or lipid structures? --Eleassar777 16:26, 24 May 2005 (UTC)

Well, I just think that lipid bilayers are recognized as being so different than ex. micelles (maybe that's just my bias as a biophysicist) and monolayers. Also, large lipid vesicles for example consist of bilayers, so they are not bilayers, but a specific architecture for bilayers, which can be planar or closed surfaces. That said, I very much agree that there should be more information on lipid aggregate structures - as a section in the page on lipids or as a new article (although I think the first option is better). I would happily do this myself, but I'm working on a different topic just now. Karol 17:06, May 24, 2005 (UTC) P.S. look: the lipid page has something on aggregates already that could evolve into a section maybe

Model Over an aperture between two aqueous solutions, where it is called a black BLM.

Huh? This doesn't make sense. --mgambrell 20:32, 9 October 2006 (UTC)

This whole article is terrible, very poorly written. I've tried to address some of the problems, but it needs some serious work. Maybe it should be entirely re-written from scratch ----fraybentos 11:32, 14 Nov 2006 (UTC)

Bimolecular layer?

Is a lipid bilayer also called a bimolecular layer? -Velen117 08:11, 12 September 2006 (UTC)

Never heard of such a term. So, probably no. However it is the samething as a phospholipid bilayer--Biophysik (talk) 12:30, 15 January 2009 (UTC)

Fluidity

No one has mentioned the fluidity of the membrane, the fact that each phospholipid molecule swaps positions with its neighbour 10 million times a second!

GA Review

This review is transcluded from Talk:Lipid bilayer/GA1. The edit link for this section can be used to add comments to the review.

I am reviewing this article. Diderot's dreams (talk) 05:04, 18 February 2009 (UTC)

Review status: on hold The article really is an excellent piece of work. It is well written, broadly, and clearly covers the topic, is properly referenced, is NPOV, has no original research, is well illustrated, etc.. It is a great upper division level treatise on lipid bilayers. But that is the problem: the article is too technical and too long for an encyclopedia article on lipid bilayers. It wears on the reader too much, especially the general reader, who may just want the basics.

I suggest summarizing more, and putting some (but not most or all) of the detailed information in sub-articles. Maybe the article could be 2/3rds of its present size. My first suggestion is the in depth analysis of characterization methods. And try to write more simply and directly when possible without losing ideas. (e.g. maybe the section should be called "Characterization methods" or "Characterizing lipid bilayers"). Lastly the introduction needs to summarize the article more. Everything discussed there shouldn't only be there, and most every section should have a mention in the introduction.

Anyway, there is a lot to praise in this article, even beyond good article criteria. I think it could easily jump straight past good article to featured article with these suggeted changes. Oh, there was a minor deal with the see alsos out of place, but I've moved them.

Diderot's dreams (talk) 05:34, 21 February 2009 (UTC)

Thanks for the review and feedback. I definitely intend to go back and do some more work on the intro, so it's good to hear some concrete ideas on what is needed. I also intend to trim the article some more, especially since I have more detailed versions in the sub-articles. I've found it challenging to decide what level of detail to keep, though. Some of the sections like mechanics are intrinsically technical. I certainly could include lower-level descriptions of the subject matter, but I'm not sure what the target audience would really be. I sort of feel like anyone interested in the mechanical properties of bilayers would be willing/able to approach the subject at a more advanced level. But maybe that's not a good assumption. What are your thoughts?

The other area where I found myself running into this issue was in the very bio-specific sections. It's hard to write an accurate/complete description without including sort of obscure terminology. Would you be willing to go through some of the sections with me and give a more detailed description of what you think should stay or go and how I might alter the tone? Thanks again for your time and help. I'd love to continue working on this to bring it up to FA. MDougM (talk) 02:48, 23 February 2009 (UTC)

I've done some copyediting to give you some specific examples of simpler wording. I think now that a basic explanatory sentence or two at the beginning of the major sections help would be a good idea for the basic reader and makes it easier to go from there, and I tried to add them. Erudition and complex structure used in general as much as specific terminology wears down the reader. Many of the technical terms just need to be there, and I think it is harder to simplify wording as you get more into the details. I am not totally happy with my new prose's style, but you can see that the information is clearly portrayed, and it really says the same thing as the old prose.

As for reducing some sections by getting rid of information, just summarize subsections in a couple of sentences and eliminate the subsection. I'll try this myself if I have time. Diderot's dreams (talk) 17:05, 24 February 2009 (UTC)

Notes and What's left to do

I have done some condensing of the Characterization methods section and put the old text on the talk page for your use. Oh, my advice about how to reduce a section should have been prefaced by if you can't think of anything better, which I think both of us have.

As for article size, it's ok to be a little larger than I recommended before. There's a lot of references here, and they aren't part of the main body and read by the reader. So maybe 3/4 rather than 2/3 of the original 88K.

The last thing is the introduction. It still needs to summarize most every section. And that should do it!

Diderot's dreams (talk) 05:44, 26 February 2009 (UTC)

I am going to close the review over the weekend and give a final evaluation, so please finish any changes by the end of Friday. Thanks! Diderot's dreams (talk) 15:12, 3 March 2009 (UTC)

After reading the article again and getting a word count with MS Word, I think you guys should know I think the article is now clear enough and short enough for GA. And I've added a paragraph summarizing the left out sections in the lead. That makes 5 paragraphs, so the lead still needs some condensing to make 4 paragraphs, which I'll leave to you guys. Diderot's dreams (talk) 16:43, 3 March 2009 (UTC)

Thanks for the heads up. I've gone through and made a few more minor changes. One of these was to incorporate the parts you added to the intro. So at this point it's four paragraphs again, but still rather long. I've trimmed it in a few places and it's now about the same length as the intro for Action Potential, but that is one of the longer ones I've seen.

I've looked around at some of the featured articles on similar topics to get an idea of how to address this. Looking at DNA and Enzyme for instance, they actually don't mention several of the sub-sections. The DNA intro doesn't mention chemical modifications, recombination, evolution, technology or history. Instead, the inro focuses on clearly expressing the basic concepts. I can see the merits of this approach, since I think most people who are only going to read the introduction would be better off having a good idea of what DNA is rather than a lot of individual facts about its properties or applications. I think the same is probably true for lipid bilayers.

So, basically, what I'm saying is that I don't think the introduction can be shortened much more if it's to retain references to each section. I'm sure I could trim a word here or there, but overall I think it will lose cogency if I try to compress much more. On the other hand, I'd be happy to try to shorten it by removing some of the information such as the single sentence (or sub-sentence) references to some of the sub-sections. I can see the merits of either format. Thoughts? MDougM (talk) 06:48, 4 March 2009 (UTC)

First let me say I think the lead is short enough as it is now. It's a long article so the lead is a little long too. Good job.

I think including almost (and I do mean almost) all sections is always doable and important. For example, those two sentences I added killed three birds with two stones. And they went well together one topic to the next. I don't really think they were isolated facts, but relevant to the story. As a last point: the leads are going to be used as the articles in the upcoming print version of Wikipedia.

There are also other ways of handling the basics besides in the introduction. A short first section on the prerequisite science with a bent toward making it applicable to the subject, e.g. one about "Intermolecular forces and membranes" could be created (not that you need to, just a hypothetical).

I don't know why those articles you mentioned skipped sections in the lead. You might want to look at the articles when those articles were passed as GAs (not FAs). It could also be that the reviewer thought it appropriate to make an exception, which is allowed because of the loose structure of our rules (the Manual of Style is in fact a guideline that says you can make exceptions), it is just against my editorial judgement. It's also possible that less constructive reasons were the cause for making an exception. Maybe their wikifrends from the same wikiproject did the GA (that's a GA no-no, but I've seen it recently and I wonder how common it is), or that the person was so impressed with the scientific knowledge or academic credentials of the writer that they were cowed over.

Anyway, I'm going to give the article another look over later tonight and see if I can pass it as I think you've satisfied all my holds. Diderot's dreams (talk) 03:44, 5 March 2009 (UTC)

Final GA Review status

Congratulations! Lipid bilayer is now a Good Article.

The objections that had this article on hold have been sufficiently resolved, and having all the other requirements already fulfilled, I am happy to promote the article. Well done to all who worked on the article, especially MdougM.

It's the last task of a reviewer to add suggestions for further improvement. I sound like a broken record, but I would continue working on simplicity of expression and the length of the article. I think there is still more that can be done, especially article length. Though I think it's short enough to pass for GA, it still needs work for ideal transmission of knowledge-ability. Anyway, these two things are the perennial bane of scientific articles, so I hope you will keep them in mind in your future work.

There is one other thing, which is something you may not have noticed. The page takes 1.7MB of data to load. This is fine for high speed connections, but about 15% of Americans still connect with 56K dial-up, and probably more throughout the world. So we've got to get that down. The problem is that several pictures with repeated molecules are saved in vector format (.svg). If they are resaved in pixel format (.png) their sizes will come down a lot.

Anyway I have one more thing to do, but it's getting late and I'll take care of it tomorrow. Diderot's dreams (talk) 05:35, 5 March 2009 (UTC)

Great! I'm glad to see it passed. Thanks for taking the time to review the article and advise me on the revision process. I think it's a much stronger, more readable piece now. I'll definitely keep looking into brevity and clarity to improve it further. Interesting point about the size of the article; I hadn't really considered that. It's my understanding, though, that all svg graphics are remotely rendered into png before being sent along with the page load. So I'm pretty sure that all graphics are already being sent as png. At least that's what they save as when I right click save them from the loaded page. Also, the original svg versions are several MB each. Now, that being said, two of the graphics (AFM and pore structure) account for nearly 1/5 of the total page size. I'm guessing it's because they have a lot of gradients, which png isn't good at compressing. Do you think it's worth making jpeg versions of them? That will cut down on the size significantly but, of course, it's a lossy format and not scalable. Anyway, don't worry about it if you don't have a strong opinion on the matter. I can query one of the image message boards for suggestions. And thanks again for helping to get everything in final form. MDougM (talk) 18:26, 5 March 2009 (UTC)

Yeah, you're right about them being png. And I think it would be a good idea to save those big ones as jpegs. The article text does load first and in a few seconds for slow internet connections, but it does take several minutes for the pictures. So why not give it a try. Diderot's dreams (talk) 04:34, 6 March 2009 (UTC)

No, jpegs are a poor choice for line diagrams, since it is a lossy compression method. See Wikipedia:Preparing images for upload for more details. Tim Vickers (talk) 17:25, 9 March 2009 (UTC)

Original Characterization methods section

Here is the original Characterization methods section before my recent edit, for use in subarticles or readds:

Human red blood cells viewed through a fluorescence microscope. The cell membrane has been stained with a fluorescent dye. Scale bar is 20µm.

Further information: [[:Lipid bilayer characterization]]

The physical nature of the lipid bilayer makes it a very difficult structure to study. An individual bilayer since it is only a few nanometers thick is invisible in traditional light microscopy. The bilayer is also a relatively fragile structure since it is held together entirely by non-covalent bonds and is irreversibly destroyed if removed from water. In spite of these limitations dozens of techniques have been developed over the last seventy years to allow investigations of the structure and function of bilayers.

Electrical measurements are the most straightforward way to characterize one of the more important functions of a bilayer, namely its ability to segregate and prevent the flow of ions in solution. Accordingly, electrical characterization was one of the first tools used to study the properties of model systems such as black membranes. By applying a bias across the bilayer and measuring the resulting current, it is possible to determine the resistance of the bilayer. This resistance is typically quite high, often exceeding 100 GO since the hydrophobic core is impermeable to charged species. Because this resistance is so large, the presence of even a few nanometer-scale holes results in a dramatic increase in current. The sensitivity of this system is such that even the activity of single ion channels can be resolved.

File:Annular Gap Junction Vesicle.jpg?

Transmission Electron Microscope (TEM) image of a lipid vesicle. The two dark bands around the edge are the two leaflets of the bilayer. Historically, similar images confirmed that the cell membrane is a bilayer

Electrical measurements are a useful tool for studying bilayer properties, but they do not provide an actual picture like imaging with a microscope can. Lipid bilayers cannot be seen in a traditional microscope because they are too thin and therefore do not interact sufficiently with light. In order to see bilayers, researchers often use fluorescence microscopy. In fluorescence microscopy a sample is excited with one color of light and observed in a different color of light, such that only fluorescent molecules with a matching excitation and emission profile will be seen. This specificity allows sensitive measurements with low background signal. Most materials, including natural lipid bilayers, are not fluorescent. Therefore, to use fluorescence microscopy to study bilayers, a fluorescent dye must be used. The resolution of fluorescence microscopy is typically limited to a few hundred nanometers, which is much smaller than a typical cell but much larger than the thickness of a lipid bilayer. More recently, advanced microscopy methods have allowed much greater resolution under certain circumstances, even down to sub-nm.

Illustration of a typical AFM scan of a supported lipid bilayer. The pits are defects in the bilayer, exposing the smooth surface of the substrate underneath.

When researchers need higher resolution than optical methods can offer, they can use electron microscopy to study lipid bilayers. In an electron microscope, a beam of focused electrons interacts with the sample rather than a beam of light as in traditional microscopy. In 1960, when the structure of the bilayer was still debated, it was electron microscopy that offered the first direct visualization of the two apposing leaflets. In conjunction with rapid freezing techniques, electron microscopy has also been used to study the mechanisms of inter- and intracellular transport, for instance in demonstrating that exocytotic vesicles are the means of chemical release at synapses.

Another method that has been used in recent years to image and study lipid bilayers is Atomic force microscopy (AFM). Rather than using a beam of light or particles, AFM uses a small sharpened tip to scan the surface, much the same way a record player works. AFM is a promising technique because it has the potential to image with nanometer resolution at room temperature and even underwater, conditions necessary for natural bilayer behavior. Another advantage is that AFM does not require fluorescent or isotopic labeling of the lipids, since the probe tip interacts mechanically with the bilayer surface. Because of this, the same scan can image both lipids and associated proteins, sometimes even with single-molecule resolution. In addition to imaging, AFM can also probe the mechanical nature of lipid bilayers.

References

Question

This is a great article. One question about the lead. It says "Cell membranes are almost always made of bilayers in the fluid phase" - I hesitated to change this, since you're the expert, but I personally can't think of any counterexamples. What examples were you thinking of? Tim Vickers (talk) 17:25, 1 March 2009 (UTC)

Certain species of archaea use a lipid monolayer rather than a bilayer. This is an adaptation to their role as extremophiles. At very high temperatures a monolayer is more stable than a bilayer. There are also a few other unique several adaptations present, including the use of an ether headgroup linkage and isoprene sidechains on the tails. Thanks for the edits. I think they help the intro read more clearly. My remaining concerns are whether the intro is still too long and whether it adequately addresses each sub-section. What do you think? Also, what do you think about the overall length of the article? Is there anything else I need to address before FA submission? MDougM (talk) 21:22, 1 March 2009 (UTC)

Good point, we can still simplify and generalise this "Cell membranes are made lipids in the fluid phase, in part because fluid lipids can reseal small holes and tears." Tim Vickers (talk) 22:27, 1 March 2009 (UTC)

OK, that's probably as general as we can make it. Have you ever heard Einstein's aphorism about explaining science that is very applicable to writing Wikipedia articles - "Make things as simple as possible, but no simpler"! Tim Vickers (talk) 23:11, 1 March 2009 (UTC)

Commercial applications / removed Planar patch clamp diagrams

The diagram / photo referring to Planar patch clamp did not illustrate the section text, their presence thus confused the reader because section had no text at all referring to this highly specialized topic. Illustrations can be readily found in the PPC article itself, therefore I have removed them and linked to Planar patch clamp at the right text position where automated patch clamp systems are mentioned. Furthermore I have replaced the commercial nanion weblink with a link to the PPC article by Behrends and Fertig on the nanion site. Regards, --Burkhard (talk) 22:03, 28 February 2010 (UTC)

Aquaporins?

The section on diffusion should be edited to include new information on aquaporins and their role in osmosis. —Preceding unsigned comment added by Quadral (talk • contribs) 02:22, 16 September 2010 (UTC)

Use of Units

The "Structure and Organisation" section of the article seems to alternate between using angstroms and nanometres for measuring distance.

For clarity and ease of understanding, wouldn't it be better to stick with one unit type? Preferably nanometers since they are an SI defined unit, whilst angstroms are not?

Also, if angstroms are to be kept due to their common usage in biology, can the link on the Å symbol be changed to direct to the Angstrom article instead of the article for the actual Å character? It just confused me first time round!

Cybernetic cheese (talk) 20:14, 5 October 2010 (UTC)

Good point. I went ahead and changed everything to nm. MDougM (talk) 15:54, 17 March 2011 (UTC)

overly technical detail in Structure and Organization?

It seems like the paragraph led by "Phospholipid-deficient mixed lipid bilayers" is perhaps too technical for this general article. Unless someone has a good counter-argument, I'll remove it from the main article and post it here so that it could maybe be spun off into a subsidiary article. — Preceding unsigned comment added by MDougM (talk • contribs) 00:13, 7 March 2015 (UTC)

I agree that that paragraph is too technical as written. Perhaps, after some editing, it could be moved to the "Mixed Systems" section of Lipid bilayer phase behavior? Shanata (talk) 09:05, 7 March 2015 (UTC)

I went ahead and removed that section. Pasting here for posterity so that it can be moved to a more appropriate home at some point MDougM (talk) 20:46, 7 March 2015 (UTC)

Phospholipid-deficient mixed lipid bilayers are unique to plant thylakoid membranes. Earth's most abundant biological membrane system, plant thylakoid membranes, surprisingly, contain largely reverse-hexagonal cylindrical phase forming monogalactosyl diglyceride(MGDG) and only 10 percent phospholipids. However, the second most abundant lipid, digalactosyl diglyceride forms aqueous lamellar phase or lipid bilayer organisation. Nevertheless, total lipid extract of thylakoid membranes does form aqueous lipid bilayers and unilamellar liposomes, which find matching fluidity with native thylakoid membranes - thus interpreted to consist largely of lipid bilayer lamellae. It is interesting to study subtle changes in carbon-13 FT-NMR spectral linewidths and line shapes of lipid fatty-acyl, and headgroup carbon resonances of lipids in unaggreated, reverse spherical micellar and lipid bilayer forms and note how segmental motions and fluidity gradient, characteristically change in different lipid dynamic organizations. Extent of resonance line broadening depends upon restriction of segmental motional freedom. For example, lipid headgroup (hg) is maximally broadened in reverse micellar (B) and least in un-aggregated (A) and in-between for bilayer (C) organisation of same lipids. Fatty-acyl carbonyl (C=O) resonance, being closest to lipid headgroups, follows almost the same line-broadening pattern. Terminal methyl (CH3) carbon resonances are only marginally broadened in lipid bilayer (C) and practically sharp in A and B. Mid-chain CH2 and HC=CH carbon resonances are also differentially broadened in the three states, depending on relatively more restriction of segmental motions in bilayer state compared to A and B. Overal examination of A, B and C states, educates about different flexibility or fluidity gradient in the three cases. Motional restriction due to 'peer pressure' on fatty acyl chains from bulk lipids in lipid bilayer organization, makes lipid bilayers show a 'characteristic', gradually-increasing fluidity-gradient conditions, from lipid head-groups to terminal methyl carbons; this becomes clear from line broadening pattern in their NMR spectra.

References

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Assessment comment

The comment(s) below were originally left at Talk:Lipid bilayer/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Lipids are as the same as the nutral cell membrane, amphiphilic molecules since they consist of polar head groups and non-polar fatty acid tails. -- This sentence doesn't make sense. What is "nutral"? And how come lipids are the same as "nutral" (I am assuming this should be neutral or natural) cell membrane? Lipids, such as triacylglycerides are used for storage, and they are not same as the cell membrane, which is made up of lipid bilayers. Can somebody please clarify or correct this sentence? (Horizonwards (talk) 21:30, 3 November 2008 (UTC))

Last edited at 21:30, 3 November 2008 (UTC). Substituted at 22:04, 29 April 2016 (UTC)

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Cytosis balancing

The article says about cytosis: The primary mechanism of this interdependence is the sheer volume of lipid material involved. In a typical cell, an area of bilayer equivalent to the entire plasma membrane will travel through the endocytosis/exocytosis cycle in about half an hour. If these two processes were not balancing each other, the cell would either balloon outward to an unmanageable size or completely deplete its plasma membrane within a matter of minutes.

I would like to change sheer volume to large amounts or similar. I don't think there is a fault here. But the word volume is ambiguous and we want to avoid association with the other meaning, which is the primary meaning according to Wikipedia.

I would also like to change within a matter of minutes to in a short time or in half an hour or something similar. This is a matter of arithmetics. If exocytosis processes an area equivalent to the plasma membrane in half an hour, then it needs half an hour to completely deplete the plasma membrane. This is a mathematical necessity. --Ettrig (talk) 10:31, 18 February 2019 (UTC)

Repetition.

The Signalling section says again some things that were already, and in my view better, explained in the Assymetry section.

Compare the following for brevity and clarity, please.

Assymettry section: "when a cell undergoes apoptosis, the phosphatidylserine — normally localised to the cytoplasmic leaflet — is transferred to the outer surface: There, it is recognised by a macrophage that then actively scavenges the dying cell."

Signalling section: " A classic example of this is phosphatidylserine-triggered phagocytosis. Normally, phosphatidylserine is asymmetrically distributed in the cell membrane and is present only on the interior side. During programmed cell death a protein called a scramblase equilibrates this distribution, displaying phosphatidylserine on the extracellular bilayer face. The presence of phosphatidylserine then triggers phagocytosis to remove the dead or dying cell." Polar Apposite (talk) 20:54, 18 November 2022 (UTC)

nonpolar attraction?

This is the first sentence of the second paragraph of the "Mechanics" section:

"As discussed in the Structure and organization section, the hydrophobic attraction of lipid tails in water is the primary force holding lipid bilayers together."

I am not qualified to edit this, but I have spent the day studying the hydrophobic effect and my understanding is that there are no attractive forces driving it. Could someone more knowledgeable fix this if it's wrong? 100.14.196.129 (talk) 22:02, 25 October 2024 (UTC)

GA concerns

I am concerned that this article no longer meets the good article criteria due to several uncited statements, including entire paragraphs. Is anyone interested in addressing this concern? Z1720 (talk) 00:49, 18 November 2024 (UTC)

GA Reassessment

Lipid bilayer

Article (edit | visual edit | history) · Article talk (edit | history) · Watch • Watch article reassessment page • Most recent review

Result pending

This article has many uncited statements, including entire paragraphs. Z1720 (talk) 22:25, 28 November 2024 (UTC)