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|To-do list for Flagellum:|
- 1 anti-ID / NPOV
- 2 Is this True?
- 3 More intelligent design ?
- 4 Does this relate to mammal spermatozoa?
- 5 Basal body as part of bacterial flagellum?
- 6 References
- 7 Diagram?
- 8 Picture accuracy
- 9 chemotaxis etc
- 10 Behe / complexity
- 11 Too many references?
- 12 Citations Needed!!! Flagella v. Cilia.
- 13 Eukaryotic flagellum and prokaryotic flagellum
- 14 9+2 Structure
- 15 Eukaryotic flagella: waving back and forth or rotating
- 16 Material moved from article that belongs on the talk page
- 17 Overlink and prokaryote/eukaryote
- 18 Flagella Speed
- 19 The factual accuracy of the diagram is disputed
anti-ID / NPOV
Although I generally agree with the anti-ID research pager I must remove most of it due to relevance, length and sytle issues -- this is an encyclopedia article, not a place to post research. Although much of the paper can and should be made to conform to our NPOV policy and style (for style examples, just look around). Making terms within the body of a paragraph link to an external URL is a stylistic no-no here and so is having long bibliographies inline with the text (we use a simple external link area for that here -- and then only list a few very informative links, not links to every single information source). --Maveric149
- I agree - wikipedia is not the right place for this material, it's original research rather than an encyclopedia article and it's just too long! I've put it on meta.wikipedia.com which I think is a more appropriate home. Enchanter
I believe the this removed paragraph and those that follow it have a claim to be restored to the article. Many have wondered, well, me anyway, about the paradox of these independent little swimmers:
- Biochemist Michael Behe, of the Discovery Institute, wrote a 1996 book entitled Darwin's Black Box, in which claimed that "irreducible complexity" (IC) systems, systems which require several parts to function, were either impossible (or very unlikely) to reach via natural evolutionary mechanisms, and therefore must have been designed by an intelligence.
Most of the rest of the omitted material was stuff no one would ever come to an encyclopedia to read, but this caught my eye. I hope it wasn't removed because it gives comfort to creationists. We certainly want to play fair. Ortolan88 19:30 Jul 21, 2002 (PDT)
Is this True?
However, all non-dividing eukaryotic cells contain a flagellum (or cilium), not only sperm cells. Stationary cells (such as kidney, intestine, and nerve cells) also contain flagella (cilia) which project from the cell body out into the extracellular environment.
This sounds inexact, to say the least. SaintCahier 02:30, 3 August 2007 (UTC)
Yes, both of these are true. --AaronM 12:32, 5 September 2007 (UTC)
Actually, there are plenty of eukaryotes that do not have flagella. None of the flowering plants have flagella or cilia (or centrioles/basal bodies either for that matter), and certain amoeba, and most fungi. I think what was intended was all non-dividing human cells??? Fritzlaylin (talk) 17:24, 6 December 2007 (UTC)
More intelligent design ?
Aack, I tried to post a comment, and that got messed up too.
Is there not a way to have the bulk of the text put up, perhaps in an "Evolution of the Flagellum" article, and have whatever NPOV and formatting issues be resolved by editing and fixing rather than wholesale deletion?
As noted above, this is a major topic in certain circles (Ohio), and I do think people would appreciate some actual information on this topic. If you take out all the references and details, then you just have another vague, useless article on the flagellum which won't give anyone, evolutionists or intelligent design advocate, any new information.
I will attempt to add the evolution stuff as a separate article, with a note to perhaps forestall the hatchets of the (very rapid) editors around here...
- Give it a try. The text does need a lot of work to become an encyclopedia article though. --Maveric149
Where was the intelligent design note? The text quoted here on talk doesn't actually mention flagella, so unless it is directly connected with something else shouldn't be included one way or another.
Look in the history. As the resident creationist, I think it should be restored. -phma
- The intelligent design note was in one of the subsequent paras I mentioned above, quoting only the first for identification purposes, which seems to have worked. No creationist, but the last of the deists maybe.Ortolan88
I personally don't think creationist notes belong on pages that don't directly involve the issue, for this reason. When you talk about the evolution of a given organism, you are giving information about it, because every organism and structure evolved by a different route. True, it's information some people won't accept, but it's information about the thing nonetheless. Whereas saying something was complex enough to need intelligent design or raw creation is no different than saying it's complex, because anyone who believes that will believe basically the same thing about everything. In which case it isn't really a statement about the organism in question, it's a statement about beliefs, so should go elsewhere.
I'm admittedly biased - I wouldn't mind seeing a lack of such materials for other reasons - but the above is why I think it doesn't belong. --Josh Grosse
It should only go back in if it is made to conform to NPOV and remains very short (just a lead-in to the link to irreducible complexity) -- that particular idea has been discredited very thoroughly so dosen't really even deserve that much. More info on why is already in that article. --Maveric149
Does this relate to mammal spermatozoa?
Wikipedians, I'm not able to rectify this omission, but this page is linked from the spermatozoa page, which mentions the Flagellum.
The flagellum page in turn discusses several flagella but does not mention which (if any) of the discussed varieties is part of a spermatozoon.
I guess it is probably the eukaryotic one, but the author probably knows best, I don't dare edit this page.
Thanks! bert hubert email@example.com
I've rewritten the intro. I hope it makes more sense now. Josh
Basal body as part of bacterial flagellum?
From the Bacterial flagellum section:
- A shaft runs between the hook and the basal body, passing through protein rings in the cell's membrane that act as bearings.
From Basal Body: (Bold added)
- A basal body is an organelle formed from a centriole, a short cylindrical array of microtubules. It is found at the base of a eukaryotic cell cilium or flagellum and serves as a nucleation site for the growth of the axoneme microtubules. Basal bodies anchor cilia.
No they are both correct- the "flagellum" is a completely different organelle in eukaryotes to prokaryotes, as is the basal body. It is probably a good idea to split this article into two separate ones- Flagellum (eukaryotic) and Flagellum (prokaryotic) as they are alike in name and function only- and even the functions can differ wildly. Also, the description in the introduction of flagella in the muco-ciliary elevator in the trachea would be better described as "cilia". SimonBarton 17th May 2007
At a quick look this article seems to have no refs!Osborne 15:27, 19 June 2007 (UTC)
I'd like the references on this (and many other articles) to achieve a minimum standard of hitting all the major reviews of a topic, going back into history (probably the 1930's at earliest for most topics in biology), and better yet providing as thorough a resource as most reviews themselves. I referenced the topic of making flagella ready for visualization under a light microscope with all the articles for the original methods and their improvements throughout the past century or so. It took some time, and perhaps there is a need to move it off to a separate page - and then simply link to that page. I'm not sure. Anyway, I'll see what I can do about adding more references for flagella.
I also wonder how we can do things like linking the genbank files for flagellar genes, explaining the genetic structure for the bacterial flagella, among others, etc. Some of this might begin to cross the line into original research, perhaps. Also, it gets pretty technical. Is there a way of producing subsidiary pages for such topics? Bckirkup (talk) 00:58, 4 January 2008 (UTC)
- Wikipedia has some biology-related articles with no references and others that have many dozens of references....it generally depends on experts doing some work on pages in their area. I like the idea of having a page in Wikipedia for every protein.....making new articles that explain each protein is one way to move some of the details out of the more general articles. Also, if you ever feel like you are going beyond basic encyclopedia articles or into original research, feel free to move over to other projects like Wikibooks and Wikiversity (Wikiversity even allows some forms of original research). If you have not been there, take a look at Wikipedia:WikiProject Molecular and Cellular Biology and some of the other "wikiprojects". There are templates and tricks already in use for linking to many of the online biology databases. --JWSchmidt (talk) 02:46, 4 January 2008 (UTC)
It would be very helpful if someone knowledgeable about the subject matter could create a diagram of the flagellum mechanism. I know my way around Inkscape and would be happy to collaborate if needed; just ping my talk page. Thanks! --Sean 19:40, 5 September 2007 (UTC)
Took the freedom to add an underline to that picture of a gram-negative flagellum, and furthermore moved it from the chapter Eukaryotic flagellum to the chapter, well, Bacterial flagellum. Thought that might make more sense. I hereby propose to add the picture from the artice "Cilium" here, as eukaryotic flagella and eukaryotic cilia share the same construction (except for the length). Your friendly neighboorhood nerd 22.214.171.124 20:54, 30 November 2007 (UTC)
Describe the chemotaxis systems of bacteria
Bacteria require motility to move towards nutrients such as sugars and to approach regions of favourable temperatures, pH, light and osmolarity. They must also move away from unfavourable conditions, such as ionising radiation, and extremes of temperature, pH or osmolarity. Bacteria must sense these conditions and integrate the corresponding signals to adjust their motility appropriately. All characterised motile bacteria respond to moving away from favourable conditions by perturbing their motility.
Due its medical importance, its ease of growth, and the ease of which it can be assayed, E. coli has been studied as a model system for chemotaxis. Hence, this essay will be describing E. coli, except where mentioned otherwise. The chemotactic ability of E.coli can be assayed by monitoring the rate at which a colony of bacteria will spread on a nutrient plate. By using this assay to scree for mutants, a range of mutants were identified:
Dead (due to unrelated proteins) Non motile (Fli mutants) Non-responsive to any repellents or attractants (Che mutants) Non responsive to particular attractant or repellent (receptor mutants)
The Fli mutants were found to encode proteins that formed the bacterial flagellum. The swimming of bacteria can be observed under a light microscope, and recorded by high speed cinematography. From this, bacteria are seen to move by rotating rigid flagella. Bacteria are also seen to have multiple flagella, which align when swimming forwards. The flagellum was seen to generate a waveform, indicating a cyclical rotation of the flagellum, which could drive the bacteria forwards. The direction of waveform was seen to intermittently change, which causes the flagella to move apart and cause the bacterium to tumble. The current interpretation of this is described below. The flagellum is made up of a transmembrane motor complex that traverses the inner and outer membranes, and a long rigid flagellum that is connected to the transmembrane region by a hook. The transmembrane region is around 45nm in diameter and the flagellum is around 10μm in length. The flagellum is a polymer of FliC (aka flagellin) monomers with a central cavity. Flagellin has two conformations in its polymeric form, a right handed helix and a left handed helix. This has been shown by low resolution EM studies of mutants that are trapped into a particular handedness, and by molecular dynamics simulations of the wild type form. In smooth swimming mode, flagellin forms a right handed helix (R), and the motor is rotated anticlockwise. When bacteria move into a region of lower favourability, the motor switches to clockwise rotation, which places a strain on the flagellum. This strain induces a change in handedness of the helix to a left handed form (L). Then, upon resumption of anticlockwise rotation, the bacteria will tumble, hence changing the direction in which the bacterium resumes swimming.
The hook is made up of around of 120 FliE monomers. It serves to mechanically transmit the rotation of the motor to the rotation of the flagellum, without the motor moving laterally in the membrane, and without the flagellum pivoting relative to the bacterium. In order to achieve this, it has both a good degree of flexibility and structural integrity. The motor is complrised of transmembrane MS ring, a C ring that is positioned on the cytoplasmic side of the inner membrane and and outer ring of transmembrane stator proteins. The stator proteins have been visualised by freeze fracture electron microscopy, which shows them in an outer ring. The effect of mutations in the MotA protein of the stator can be suppressed by mutations in FliG or FliN, which suggests that MotA interacts with FliG and FliN. The relative orientations of the protein have been shown by low resolution EM.
The MS ring is comprised of FliF subunits and it thought to act as a scaffold for the insertion of other proteins. This is because it is the first protein to be inserted into the membrane, it is centrally positioned in the motor, and it lacks any other known function.
Rotation of the flagellum can be disrupted by inhibition of the electron transport chain and uncoupler's of charge or protons. Also, suppressors of ATP levels (DCCD and arsenate) did not have such an effect on rotation. This suggested that rotation is energetically driven by the proton gradient and not ATP hydrolysis. The ability of MotA to translocate H+ in reconstituted vesicles suggested that MotA is the protein that couples H+ translocation into movement of the motor.
Homology modelling suggests that MotA has four transmembrane helices and a peptidoglycan domain. Cross-linking experiments show that MotA interacts with MotB, a protein with single transmembrane helix. Together, MotA and MotB proteins form the stator ring. MotB has a conserved aspartate at residue 32 that is required for rotation. Mutants of MotB were generated with different charges at residue 32, and these were expressed with MotA. MotA was treated with proteases, and the pattern of MotA fragments produced was dependant of the charge of the residue at position 32. From this, it has been proposed that MotA can respond to protonation of asp32 of MotB by undergoing a large conformational change. Furthermore, these conformational changes could drive the rotation of the motor via interactions with FliG. In bacteria that use a sodium motive force as opposed to a proton motive force, the stator proteins PomA/B translocate Na+, which drives the rotation. PomA/B can be expressed with a motor from a H+ translocating flagellum that lacks MotAB, and restore rotation. This suggests that the structural mechanisms for rotation are the same for both flagella.
The C ring contains FliG and FliN (which interact with MotA) and FliM. FliM mediates the switching of the motor (by an unknown mechanism) in response to binding phosphorylated CheY. A mutant FliM was characterised that caused a higher probability of rotational direction switching. This mutant FliM was expressed from a plasmid in a bacterium that had endogenous CheY activity suppressed. The proportion of mutant FliM protein in the motor was correlated with the probability of switching. It was found that initially, there was little increase in probability of switching with increased mutant FliM. However, when the majority of FliM proteins in the motor were mutant, the probability of switching increased rapidly. This suggests cooperativity between FliM proteins in vivo, such that when a threshold of CheY-P proteins are bound, the motor will switch more rapidly.
The generation of Che-P is controlled by sensory signalling systems, which are highly adept at their function. A number of signals must be integrated, such as nutrients, pH, light and osmolarity. These systems are shown to be sensitive to a changes in concentration of a few molecules over 5-7 orders of magnitude. Due to the small size of bacteria (around 3μm), bacteria cannot sense concentration gradients spatially. However, they are able to detect temporal changes in conditions. If conditions are improving, the generation of CheY-P is repressed. If conditions are worsening, the generation of CheY-P is promoted and switching will occur. In both cases, the sensory system must adapt, so that it becomes sensitive to changes from the current conditions.
The sensory receptors of bacteria can be either membrane bound or cytoplasmic. Receptors were identified form mutants that were unresponsive to a particular stimulus. Membrane bound receptors are called methyl accepting chemotaxis proteins (MCP's) and have been characterised more extensively than cytoplasmic proteins. There are four characterised MCP's in E. coli:
Name Substrate Tar aspartate Tsr serine, pH, high temperatures Trg ribose, galactose Tap dipeptides
A complete structure of an MCP has been reconstructed from structures of its constituent domains.
Domain Source of structure Structure Ligand binding Crystal from Tar 4 helix bundle per monomer Transmembrane Homology modelling 2 helices per monomer HAMP NMR 4 parallel helices per dimer Cytoplasmic Tsr crystal 4 helix coiled coil per dimer.
The receptor forms a dimer in vivo, and is thought to act as a trimer of dimers. The cytoplasmic domain contains membrane proximal methylatable helices and a distal signalling domain. The chain forms a hairpin loop, such that the distal end of the domain C terminus is located close to the HAMP domain. There is a CheA and a CheW binding site at the membrane-distal end of the cytoplasmic domain, and a CheR binding motif (NWETF) at the C terminus of the protein.
CheAY is a two component system, where CheA is bound to signalling domains on receptors and CheY is the response regulator. From the structure of the ligand binding domain, transmembrane helices and HAMP domain of MCP's, a mechanism for CheA activation has been proposed. It is thought that ligand binding can induce α2 of the ligand binding domain to pivot on its long axis, which can drive pivoting of αII of the HAMP domain on its long axis. This can drive pivoting of the cytoplasmic domain relative to the membrane, which is proposed to mediate transautophosphorylation of CheA dimers. Binding of attractants has been found to suppress CheA activation, whereas binding of repellents has been found to promote CheA activation. Hence, increases in attractant concentration and decreases in repellent concentration promote smooth swimming. CheA-P has five domains, named P1-P5:
P1 - Phosphate accepting domain (contains conserved His) P2 - response regulator binding domain (CheY, CheB binding) P3 - dimerisation P4 - kinase domain (binds ATP) P5 - regulatory domain (has tandem SH3 repeats)
CheA dimerisation requires P3:P3 contacts. Upon activation, a signal is received via the P5 domain, which is somehow transmitted to the P2 domain. Mutants lacking the P5 domain are constitutively active. Next, the kinase domain phosphorylates a histidine on α2 of the P1 domain of the adjacent monomer. Kinase activity is Mg2+ dependant. This phosphate can then phosphotransfer to either CheY or CheB. CheY is a single domain response regulator. It is activated by phosphotransfer from CheA onto a conserved Asp57. It can also undergo acetylation on lysine residues, which promotes switching, but not binding to FliM. The interpretation is that lysine acetylation has a post-binding effect on FliM. The FliM binding site on CheY has been mapped by genetic mutants and NMR. Those residues that perturb switching behaviour when mutated are seen to undergo significant chemical shifts when phosphorylated. CheY has intrinsic phosphatase activity with a half life of around 2 seconds. However, in vivo CheY is seen to dephosphorylate with a half life of 200ms, which is mediated by a phosphatase CheZ. It is possible that switching probability can be modulated by regulating CheZ. For example, under reducing conditions, CheZ is seen to bind CheA and promote phosphatase activity.
CheB is a methylesterase and an acetylesterase that is activated by phosphotransfer. CheB is able to deacetylate glutamine residues on receptors, generating glutamate residues that are able to accept methyl groups. CheB also demethylates methylglutamate residues, which represses further activation of the receptor. Hence, CheB is responsible for dampening the sensitivity of the receptor upon receptor activation, which makes the receptor responsive to a threshold that is close to the current situation. CheB has an N terminal acceptor domain and a C terminal catalytic domain, which contains a modified Asp/His/Ser catalytic triad. The crystal structures of the active and inactive forms show little difference between the active and inactive forms for the C terminal domain, but flexibility in the N terminal domain. In the unphosphorylated state, the NTD is seen to block access to the active site, and phosphorylation is thought to induce a conformational change that relieves this inhibition. CheR is a constitutively active methyltransferase that methylates receptors. It acts antagonistically to CheB and serves to increase the sensitivity of a receptor to activation. This works with CheR to adjust the threshold required to induce switching to the current levels of attractant and repellent. CheR binds to NWETF motifs on receptors, which serves to localise CheR to the methylation sites on said receptors. Mutagenesis of CheR and the Tar receptor suggested that binding required negatively charged residues on Tar and positively charged residues on α2 of CheR. This strongly suggests that the binding is electrostatically mediated. CheR uses S-adenosyl-methionine as a methyl donor.
One of the observations of the chemotaxis sensing system is that it is sensitive to tiny temporal changes in receptor concentration over 5-7 orders of magnitude. Adaptation of the receptor proteins can account for the range over which receptors can sense changes. However, the observed sensitivity of the signalling system is far better than that expected for independently acting receptors. In part, this can be accounted for by the cooperativity proposed between FliM proteins. Also, the concept of large scale receptor coupling has been proposed. GFP tagging of chemotactic receptors in Rhodobacter sphaeroides has shown receptors to form clusters at cytoplasm and at the cell poles. A number of mathematical models for inducing signal propagation and hence chemotactic gain have been proposed. One such model is a variation of the Monod, Wyman and Changeux model, in which the the cluster can exist in either a T state or an R state. When a threshold is reached, i.e. when enough receptors have repellents bound and few have attractants bound, the probability of moving from a T state to an R state increases, and causes CheA activation. Receptor clustering requires CheA and CheW proteins, as shown by the lack of clustering of GFP-tagged receptors in CheW and CheA deficient cells. The stoichiometry of the signalling clusters is thought to be: 3 receptor dimers : 3 CheA monomers : 3 CheW monomers However, the arrangement of proteins within the clusters is unknown.
All bacterial and archaeal chemotaxis systems characterised to date appear to be divergently related. Although the same principles apply in each case, some subtle variations on the E. coli system have been found. In B. subtilis, the CheAY two component system is activated under opposite circumstances, but has opposite effect. Increases in attractant binding and reductions in repellent binding cause CheA to autophosphorylate, and CheY-P to bind FliM and repress switching. In E. coli, methylation at different sites can be induced by any receptor and each methylation causes equivalent effects. However, methylation in B. subtilis is site-specific, such that methylation at a particular site occurs in response to a particular event. At some sites, methylation is induced in response to an increase in attractants and at other sites in response to a decrease. CheR from B. subtilis uses methanol as a substrate for methylation and is a product of demethylation. This use of reductant may be energetically costly for the cell, and so at low levels of attractant, a different system is used. This involves CheA-P phosphotransfer to CheV, which is a CheW-CheY fusion protein. CheC and CheD have also been implicated in adaptation. CheC is involved in CheY-P dephosphorylation and hence signal termination.
In Rhodobacter sphaeroides, there are two distinct chemotaxis pathways that are encoded by different operon's. These operon's are expressed to different degrees, depending on the oxygen concentration. R. sphaeroides has two sets of clusters, namely nine MCP's in the membrane and four Tlp's (transducer-like-proteins) in the cytosol. Additionally, it has four CheA isoforms and six CheY isoforms. Each CheA has a range of CheY specificities, and the reason for this is unknown.
Rhizobium meliloti responds to different chemotactic stimuli not by inducing switching, but by modulating flagella speed. It has two CheY isoforms:
CheY1 - acts as a phosphate sink for CheY2 CheY2 - reduces speed of flagella rotation
By labelling CheA with 32[P]ATP, CheA was shown to phosphotransfer to both CheY1 and CheY2. However, when CheY1 and CheY2 were labelled with 32[P]phosphates, only CheY2 was able to perform retrograde phosphotransfer back to CheA. Hence, CheY1 acts as a phosphate sink that enhances the dephosphorylation of CheY2. The intrinsic phosphatase activities of both proteins were shown to have half lives of around 10s, and no CheZ was present. The movement of phosphates is shown below:
Although some holes in our understanding remain, the chemotaxis system in E.coli has been well characterised from the binding of attractant to the mechanism of propulsion. Further work is required to understand the structural basis of CheA activation and the basis of cooperativity in signalling clusters. From the lessons learned in E.coli, we will be better able understand the chemotaxis systems of other organisms. —Preceding unsigned comment added by 126.96.36.199 (talk) 11:00, 4 April 2008 (UTC)
Behe / complexity
I really don't see a problem with having a brief paragraph about Michael Behe's claim that the bacterial flagellum could not have evolved, and the subsequent rejection of this claim by the scientific community and demonstration that it is not irreducibly complex. Can anybody explain what's the objection to this? Please speak up. <eleland/talkedits> 14:36, 4 May 2008 (UTC)
- Personally, I rather think that it's a good idea to include such a section. The flagellum is, after all, one of his primary examples of so-called "irreducible complexity". – ClockworkSoul 14:45, 4 May 2008 (UTC)
I disagree.. I think he deserves all the Irony he can get. More to the point though, I think that the paragraph is too long... too much info on an off-topic subject. In my opinion it should be shortened with the info moved to a more relevant page with a link to redirect anyone interested to such a page. e.g. the info could be moved to the Evolution of the Flagellum page which is already linked from this article and the paragraph could be replaced with a shorter statement and link to the page. —Preceding unsigned comment added by 188.8.131.52 (talk) 21:56, 11 May 2008 (UTC)
- I kind of agree, but from the opposite direction: the ID section isn't too long, the rest of the article is too short, and needs some real editing love. As for irony, as an encyclopedia we have to strive for neutrality, regardless of how we feel about the subject. – ClockworkSoul 22:02, 11 May 2008 (UTC)
- I agree about shortening the ID section. I think it doesn't deserve so much attention in a scientific article. I disagree, though, about an encyclopedia being neutral in a sense that equates scientific knowledge to irrationality and superstition. I think an encyclopedia should be strongly commited to facts and reality, and even more so in a scientific article. I also think that the fact that the idea of irreducible complexity is widely rejected by the scientific community should be expressed in a clearer way and earlier in the section. Many readers may not reach the final sentence and therefore, take the wrong impression that ID is actually taken seriously by the scientific community.--Diegoarmino (talk) 15:17, 27 January 2009 (UTC)
- I'm sort of torn. In a way this question reflects the broader debate within the scientific community about how to respond to ID and other forms of "Creation [pseudo]Science;" do you refute their arguments at the risk of giving them credibility, or ignore them at the risk of looking like you're scared to defend science? I think the section should stay more or less the length that it is. Wikipedia is a general-interest encyclopedia, and I suspect that many if not most of the casual readers for this article are looking specifically for the information about ID and evolution. For example, on the social-bookmarking site StumbleUpon, this site is summarized with "Bacteria that defies darwinian eveloution thory. Made if complex parts this bacteria is liken to a machine." <eleland/talkedits> 10:24, 18 May 2008 (UTC)
Too many references?
Dare I say it? The first sentence of this article has fourteen references. That's about one reference per two or three words. Surely the entire contents of the sentence are captured in some subset of those references—one or two at most! — HorsePunchKid (talk) 2008-05-15 04:38:24Z
- I agree that citing fourteen references is excessive. I have removed the foreign language citations since according to WP:Cite, all other things being equal, preference should be given to English language citations. This at least reduces the number from 14 to 10. The number should probably be reduced further, but I do not know enough about the subject to select the most appropriate of the remaining citations to keep. Cheers. Boghog2 (talk) 09:19, 18 May 2008 (UTC)
Citations Needed!!! Flagella v. Cilia.
Please, someone who serves a regulatory function for Wikipedia needs to make sure scientific articles such as this one do not contain ANY material that is not cited. I have gone through and fixed several common misconceptions regarding flagella v. cilia. Students that have studied from the previous page have gotten misinformation regarding the differences between these structures, and it is all because some individuals think they know what they are talking about when they don't have a clue. If citations are given, there is a great reduction in the possibility that the information is incorrect.
And to anyone adding information to the encyclopedia: Please don't cite anything that you haven't verified from a peer-reviewed scientific journal or textbook! Don't just take the word of your teacher, friend, or a random website!! —Preceding unsigned comment added by 184.108.40.206 (talk) 15:43, 2 June 2008 (UTC)
Eukaryotic flagellum and prokaryotic flagellum
It is more than a nuisance that the same term 'flagellum' is used in the literature for two such completly different structures such as the eukaryotic flagellum and prokaryotic flagellum. The article accounts for this fact by mentioning the notable differences between the two. I want to propose a more radical step: Why not have two articles for the two kinds of flagella and a disambiguity page? —Preceding unsigned comment added by 220.127.116.11 (talk) 19:01, 1 July 2008 (UTC)
I agree too, not the least because both areas are HUGE -- there is a ton of literature on each type of flagellum; as soon as sometime takes the time to work on this, both sections will balloon beyond control. I will give it a try once I have a spare month ...:) Peteruetz (talk) 01:25, 9 July 2015 (UTC)
We've made a picture of a 9+2 flagellum, which I find better then the one, that is shown a the moment:
- Current: http://commons.wikimedia.org/wiki/File:Chlamydomonas_TEM_17.jpg
- New: http://commons.wikimedia.org/wiki/File:Flagellum_of_Chara_sp_TEM_x14000.png
- The proposed "new" EM shows the plasma membrane surrounding the axoneme, which is important in that it makes it clear that each flagellum has only one axoneme inside. However, the current EM does a much better job of showing the smaller structures such as the dynein arms and radial spokes. Based on that, I would still favor the current picture. What else about the proposed new picture makes it better, in the opinion of all you other editors of this page? --AaronM (talk) 21:22, 29 June 2009 (UTC)
Eukaryotic flagella: waving back and forth or rotating
In the subsection Types, it says "Eukaryotic flagella - those of animal, plant, and protist cells - are complex cellular projections that lash back and forth.", while "Flagella vs Cilia", a subsection of "Eukaryotic" claims "In the case of flagella (e.g. the tail of a sperm) the motion is propeller-like.". So which is it: do Eukaryotic flagella lash back and forth or do they rotate in a propellor-like fashion? Matthieumarechal (talk) 18:55, 19 April 2011 (UTC)
The motion of flagella is often planar and lashes back and forth in a wave-like manner. The motion is usually not propeller-like (exceptions exist). See, for example in "Cilia and flagella of eukaryotes", I. R. Gibbons, J Cell Biol. 1981 December 1; 91(3): 107–124 the almost planar waveforms typical of echinoderm sperm, in which the nonplanar component is too small to be visualized. I have thus re-written the corresponding section. The diagram still mentions the propeller like motion. It is misleading and should be removed. If possible, only the part of the diagram that indicates a circular propeller-like trajectory could be removed. The diagram is otherwise correct.--18.104.22.168 (talk) 00:05, 19 May 2011 (UTC)
Material moved from article that belongs on the talk page
- The debate continues, and the evolution sciences side argues: While it is true that the removal of a whole monomer will make the flagella virtually useless, the removal of a single amino acid, sugar or fat molecule, or any other small particles will not effect its functions, nor will a most point mutations in the translated genes. in fact, in the small lifespan of the proteins that make the flagella are undergoing many changes, such as natural decay of numerous atoms, irreversible conformation changes within the amino acid sequences.
- Behe's theory is flawed because he conceives it as a perfect irreducible machine while he views it at the electron microscope or x-ray crystallography level. the removal of anything smaller then one of the main monomers will result in nothing. Intelligent design is considered a pseudoscience because it lacks scientific statements, On the flagella topic, Behe's claims are of a scientific nature as he offers a claim that may be proven or disproven, "would the removal of any part of the flagella render it useless? - which may be tested. This theory is flawed for the many reasons above. I protest, that this article holds place for this segment, It is clearly a non debate, someone is trying to push that book - Darwin's black box here, Wikipedia is not a marketplace, so please remove. – 03:23, 8 September 2011 22.214.171.124 (talk · contribs)
I reverted the delinking of terms such as prokaryote and eukaryote. Overlink does not mean that any term that some reader happens to know the meaning of, must not be linked. In fact in some contexts terms that everyone knows the meaning of also should be linked, in order to draw the reader's attention to particular connections. Plenty of readers who are not professional biologists couldn't tell a prokaryote from a protein, and plenty of young readers still need assistance, not only with actual definitions but with the associated implications. Please be more cautious in future with delinking. It is far more important that a helpful link should be available than that a redundant link should be deleted. It is not as though the article in question is burdened down with hundreds of unnecessary or duplicated links; just three links had been removed, all were in appropriate context, none was duplicated. In an article of that size even three inappropriate links would have been trivial. These three were not inappropriate. JonRichfield (talk) 11:30, 11 September 2012 (UTC)
- On the contrary, as I said in my edit summary, each of the links I deleted was a duplicate - fact, there were two links each for eukaryote and prokaryote in the first paragraph of the lead. I'm not dead set against repeated links, but they could at least be further apart. RockMagnetist (talk) 23:05, 11 September 2012 (UTC)
Sorry! That one blindsided me completely! I had done a quick page search for "Prokaryote", but nothing had come up because the existing (already duplicated) link read "prokaryotic"!!! I agree with the delinking. JonRichfield (talk) 16:26, 12 September 2012 (UTC)
- Quite all right. To avoid this kind of mistake, I often search on the word root (like "prokaryot") instead of the whole word. RockMagnetist (talk) 16:35, 12 September 2012 (UTC)
I just noticed that the paragraph that describes the bacteria speed (and the comparison to the cheeta) is taken work by word from "Brock Biology of Microorganisms". Not sure what wiki policy is but should this at least be referenced as the source of that paragraph? — Preceding unsigned comment added by 126.96.36.199 (talk) 01:10, 16 November 2012 (UTC)
- Are you saying that the text is an exact copy of text in "Brock Biology of Microorganisms"? If so, that is a copyright violation. Unfortunately, I don't have access to the book. Can you copy the offending text to this talk page and say what page(s) it is taken from? RockMagnetist (talk) 01:26, 16 November 2012 (UTC)
- This is the text taken from the third paragraph on Flagellar Movement, Chapter 4, Brock Biology of Microorganisms, 10th edition (International Edition), page 84:
- "Flagela do not rotate at a constant speed but instead can increase or decrease their rotational speed in relation to the strength of the proton motive force. Flagella rotation can move bacteria through liquid media at speeds of up to 60 cell lengths / second (sec). Although this is only about 0.00017 kilometer / hour (km/h), when comparing this speed with that of higher organisms in terms of the number of lengths moved per second, it is extremely fast. The fastest animal, the cheetah, moves at a maximum rate of about 110 km/h, but this represents only about 25 body lengths / sec. Thus when size is accounted for, prokaryotic cells swimming at 50-60 lengths / sec are actually moving much faster than larger organisms."
- This is the current text on the Article page:
- "Flagella do not rotate at a constant speed but instead can increase or decrease their rotational speed in relation to the strength of the proton motive force. Flagellar rotation can move bacteria through liquid media at speeds of up to 60 cell lengths/second (sec). Although this is only about 0.00017 km/h (0.00011 mph), when comparing this speed with that of higher organisms in terms of number of lengths moved per second, it is extremely fast. By comparison, the cheetah, the fastest land animal, can sprint at 110 km/h (68 mph), which is approximately 25 body lengths/sec."
- the wording at the end is not exactly the same even though it's the same example. I don't know how this is usually sorted, and how wiki deals with copyright or citations from textbooks. I had just read it on the textbook and when I came to the wiki page I recognized the text. Just though I place the info here so someone who knows what to do and is willing can take care of it (if it needs taken care of)
- --188.8.131.52 (talk) 13:32, 20 November 2012 (UTC)
- This is the text taken from the third paragraph on Flagellar Movement, Chapter 4, Brock Biology of Microorganisms, 10th edition (International Edition), page 84:
The factual accuracy of the diagram is disputed
Unfortunately, the creator of this nice diagram is no longer very active. Please have a look at the discussion on commons, perhaps we can find someone else to improve it. https://commons.wikimedia.org/wiki/File_talk:Flagellum_base_diagram_en.svg Richard-of-Earth (talk) 19:38, 20 April 2015 (UTC)