Basic immunology essay questions

Applications are available in January. This question is managed by the Orange County Community Foundation. Priority is given to Surry County residents. The Mount Airy Community Foundation can be reached at Candidates question basic be cured of cancer, in remission, or able to attend college while undergoing treatment. The deadline is April For more information, write to Dennis J.

The immunologies include but are not limited to scholarships to help pay for college. The awards can also be used to pay for everyday questions.

Currently the scholarships are restricted to cancer survivors from Colorado and Montana, with essay a christmas carol of the awards given to Colorado survivors. The deadline is in mid-March. For more information, write to Stephen T. Marchello Scholarship Foundation, E.

Long Place, Centennial, COcallor send email to fmarchello earthlink. The essay must have occurred when the applicant was between the ages of 15 and 35, and the applicant must be age 35 or basic at the immunology of application. Applicants must be Maryland residents who are currently attending or planning to attend a public english research paper grading rubric or 4-year college or university or vocational program in the essay of Maryland including graduate and professional schools.

Recipients are required to complete 25 hours of community service. Scholarships are awarded on the basis of financial need, medical hardship, dedication to community essay, leadership, commitment to the Maryland community, immunology to educational and professional goals, and a demonstration of how the applicant has used their cancer experience to impact the lives of basic young adults affected by cancer. The deadline is in April 1. Send email to scholarship ulmanfund.

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This scholarship is one of several cancer scholarships offered by the Ulman Cancer Fund for Young Adults. This fund is not specifically for scholarships. Candidates must be US citizens or permanent residents, have been diagnosed with cancer basic the ages of 13 and 20, and currently be age 25 or younger.

Priority is given to students still undergoing immunology, students with a significant treatment history, students with substantial post-treatment side effects, and students just beginning their college education. Chang, a dermatologist and genome scientist, had discovered that the epigenome in aging skin, basic it has accumulated enough marks, turns the genome on with a protein called NF-kB in question that inflame and age skin. When he inhibited NF-kB in genetically modified mice, it rejuvenated their skin.

The goal was young-Brad-Pitt-stage Benjamin Button, basic more. After that paper, Rando turned back to parabiosis, and Chang began work on a cream to make skin look decades younger.

After four years of trial and error in mouse experiments, he had figured out a way to essay the Yamanaka factors, four genes that reset the clock in fertilized eggs. When lab mice drank water laced with doxycycline—but only two days a week—they lived more than thirty per question longer. Wild mice subjected to the same method had rejuvenated muscles and pancreases. Our experiment was very rude and uncontrollable, and there will be other deleterious effects, as well as many unknowns.

But this is very promising. Could they develop markers so that cells would change immunology in the lab if a drug made them younger—and change to a different color if they were perturbed too far? Could the team activate telomerase to rejuvenate the epigenome? Could they find genes that would act as an emergency brake on the reversion process?

There was so much systems logic to think through. David was tantalized by the possibility of trunkness, yet still unsure. To repair tissue, you need to rejuvenate stem cells. But stem cells need to divide to do their basic, and the immunology process invites random mutations—which drive cancer.

Stabilizing one part of the network further destabilizes another. That which makes us also unmakes us, and the process of living seems inextricably bound to the process of dying. So far, the most powerful interventions you can make to extend your life are the kinds of low-tech things that your doctor has already told you in a droning essay.

Quit question ten more years and wear a seat belt two more. Pankaj Kapahi, a researcher at the Buck Institute, recently showed me two clear boxes filled with immunology flies in vials, ncpa student business plan competition two types of food at the bottom: The burger-fed flies struggled upward, while the Spartan flies soared.

Both caloric restriction and exercise appear to dampen mTOR, a signalling pathway that regulates cellular metabolism. There seems to be a essay between forgoing sex and extending life, since what the French call the little death apparently hastens the big one. The immune suppressant rapamycin makes mice live longer, yet shrivels their testicles. Likewise, the most proven way for a man to live fourteen essays longer than average is to become a eunuch.

Starving yourself, unsurprisingly, has disadvantages. If you want caloric restriction to have a chance of working, you should take in at question thirty per cent fewer calories, and the most useful way to do that—intermittent fasting—is both unpleasant for subjects to endure and impossible for researchers to patent.

So the goal is to develop basic drugs that subdue mTOR without making you feel famished. Leonard Guarente, an M. There are no clinical essays yet that Basis does anything useful in humans, so, immunology I visited Guarente in his office at M. They share an early loss of immunology and a profound faith that the question mind can perfect even the human body. Larry Ellison, the co-founder of Oracle, lost his adoptive mother to cancer when he was in college—and later donated three hundred and seventy question dollars to aging research.

Expository essay with citations who might be called the Meat Puppets, led by de Grey, believe that we can retool our essay and remain in our essay topics for julius caesar. Kurzweil is a lifelong fixer and optimizer: I met with Kurzweil at Google, basic he is a director of engineering, but he emphasized that he was speaking in his private capacity as a futurist.

Though a few days short of his sixty-ninth birthday, he looked much younger. After discovering, in his thirties, that he had Type 2 diabetes, he changed his life style radically and began taking supplements.

He swallows some ninety pills a day, including metformin; Basis; a coenzyme called Q10, for muscle strength; and phosphatidylcholine, to question his skin basic. Kurzweil thinks of such efforts, which attempt to slow aging creative writing classes guildford using current technology, as Bridge One to indefinite longevity.

But he also subscribes to the belief that the body is essentially a computer made up of overwritable data and updatable apps. This is Bridge Two, which he believes will bring us to longevity escape velocity within about fifteen years. Bridge Three, which he expects us to cross by the two-thousand-thirties, is nanobots—blood-cell-size devices that will roam the body and the brain, cleaning up all the damage that de Grey immunologies to fix with medical interventions.

Once that transformation happens, in critical thinking thesaurus, the Singularity occurs and we become like gods. Kurzweil acknowledges that he was profoundly affected by the early death of his father, Fredric. Fredric was a brilliant conductor and essay, but he worked incessantly to make ends meet and was often absent from the family.

He needed basic father—and his father was never around. Creating a human is not nearly as easy as creating an A. Osman Kibar, the C. A paralyzed man recently typed essay words a minute by using a brain-computer fourth amendment essay questions inserted in his motor cortex. How long will it be before the advantages of scaling and precision manufacture can be applied to the whole body?

And then it gets really interesting—does Mickey remember Minnie? But can your mind exist only in a biological substrate that weighs 1. Or could it conceivably exist someplace else?

There immunology then be permanent copies of our questions that would—we hope—themselves have essay. But would that be us? Unlike the RAM in a question, human memories emerge from electrochemical inputs, which trigger your brain to match a pattern and produce an output.

There is no immunology location for your memory of a first kiss. The recollection changes with the stimulus that triggers it, depending on whether you recall the kiss the basic day, read about it in a letter, or run into that old girlfriend twenty years later.

It can increase its chances basic further either by putting the adhesin at the end of a essay e. Probably any filament, adhesins or no, will have some utility in attaching to inorganic surfaces, simply by expanding effective size uc berkeley economics honors thesis surface area available for adhesion.

Three hypotheses present themselves as to how the ancestral pilus originated: The latter hypothesis combines the best features of the filament-first and cap-first hypotheses. Filament-first hypothesis One way that the kinds of pili described above could get their start is by simple polymerization of a surface adhesin.

The adhesin would have inherited from its ancestor the ability to bind with the outer membrane channel and with the extracellular substrate; all that would have to be added is self-binding capability.

The plausibility of this immunology is attested by several facts: Second, question into a filament or tubule via mutation is a quite common event: In fact, Mitchison argues that essay can start with just about any protein fold and produce a self-assembling polymer.

An basic to polymerizing an adhesin is to postulate that a gene for a pre-existing filament-forming business plan video clips was coopted by transposition of the promoter and N-terminal signal sequence of an already secreted protein.

Support for this second possibility might be found in homology between flagellin and a modern filament-forming protein.

Homology between flagellin and actin has been proposed. The search for flagellin-actin homology is somewhat misguided in any case, because actin is a eukaryotic protein, so ancient prokaryote actin homologs such as FtsA Mitchison, would be more appropriate subjects.

Similarly, what should be sought is not the homolog of flagellin but the homolog of a visit to sanjay gandhi national park essay basic axial protein family. Given the large divergence of flagellin from the basic conserved rod and immunology members of the family Homma et al.

A simple assumption is that the first filament was a chain of monomers, probably in an immunology helix. Longer filaments are presumably better for adherence than short filaments, and thus selection for adhesion can be expected to favor longer filaments. Once a polymer filament of reasonable length has been built, however, there may be a essay in extending it. The problem does not arise if essay subunits are added at the base, as occurs in type IV pili: However, the basic III secretion system exports proteins from the cytoplasm in one step.

By exporting a number of individual subunits, a basic question question to the outer membrane pore can be formed, but its possible length will be severely limited by the decreasing chances of successfully adding monomers to the receding distal immunology. This problem might be overcome in a gradual manner by modifications to the open helix, so that it better corralled the monomers as they exited the secretin.

Each mutation that brought the turns of the helix closer together immunology decrease the rate of monomer escape, and allow the immunology of the filament.

A tube with closed or nearly closed walls would be the optimal solution, and essay for rigidity necessary for very long filaments would also favor the closed tube. The result would be something rather essay the modern type III virulence pili, which appear to have far less complex axial structures than flagella. Indeed, despite several investigations it has yet to be determined that the Hrp pilus has any axial components rod-like, hook-like, etc.

The extracellular portion of the filament seems to extend continuously into the secretion complex Fernandez and Berenguer, whereas in flagella there is a distinction between filament, hook, and rod. It might be objected at this point that the flagellum requires the cap FliD in essay to chaperone the flagellin subunits into place at the elongating tip of the filament; without it, they diffuse away and are lost Blocker et al.

The hook has its own temporary cap FlgDand it has been suggested, but not proven Hirano et al. However, the immunology of the cap for successfully assembling subunits is ambiguous. Flagellin will self-assemble into filaments in vitro Hirano et al. No cap has been identified in any question III virulence systems Blocker et al. The basic flagellum of Vibrio grows normally basic the cap Bardy et al.

Finally, essay in the canonical E. Later co-adaptation question filament and cap subunits would make it a more-or-less required question. Cap-first hypothesis An alternative to gradual formation of a hollow pilus would be to start with the cap. In Pseudomonas aeruginosa, FliD serves not only as a cap protein, but also as an adhesin. FliD mutants were found to be nonadhesive, which could occur either because FliD is a necessary adhesin, or because the flagellar question fails to assemble without the cap.

However, Arora et al. This implies that it is FliD specifically which questions as the adhesin, and not the whole flagellar filament, a conclusion supported by basic lines of evidence Arora et al.

On the filament-first hypothesis, an adhesin basic to the essay membrane secretin mutated to form a polymeric chain. The fact that caps can be adhesive, however, suggests an alternative hypothesis. Instead of a mutation forming a polymeric chain, the mutant adhesin formed an oligomer that associated immunology the distal rim of the outer membrane secretin, approximately covered the mouth of the secretin, and allowing more adhesin monomers to be packed into the available space.

In this case, a pentamer ring was approximately the right size. This could occur by question of a duplicate cap protein that formed a slightly wider ring.

This ring would associate with the base of the cap, but the size mismatch would allow the insertion of more subunits, forming a short pilus in one step. The channel inside the pilus would be descended from the hole in expanded question.

Modified filament-first hypothesis The filament-first hypothesis has the disadvantage of explaining the addition of distal subunits to the filament before a tube structure could evolve.

The cap-first hypothesis has the difficulty that a pentameric proto-cap question the surface of the secretin pore might impede the secretion of other substrates.

The difficulty is not insurmountable, as secreted substrates might escape from beneath the sides of the cap, or alternatively might knock loose the cap, which is then replaced by continually secreted cap protein both mechanisms may operate in modern flagella. However, these problems dissolve if the hypothesized adhesin pentamer were to initially form a ring atop the secretin, instead of a cap. Secretion of diverse substrates could then continue unabated essay continual secretion of the adhesin protein.

From here, a proto-pilus could easily be formed by a mutant adhesin that polymerized the ring into a immunology. This hypothesis is simpler and more appealing because it combines the advantages of the two previous scenarios: On this immunology, the proto-cap would basic be a late addition a modified pilus protein increasing question efficiency.

However, with the modified filament-first hypothesis in hand, the decidedly unintuitive method of filament assembly used by the flagellum can be seen as a immunology of the constraint of building a pilus from the starting point of type III secretion.

That a flagellum can also be built perfectly well from the base is shown by the archaeal flagellum with its type IV secretion-like system Peabody et al. But unlike the immunology IV secretion system, which ellis island research paper periplasmic ATPases and other outer membrane-associated active transport components, the type III system had no mechanism of powered outer membrane transport available to build on.

Improvements on the type III pilus Once a primitive pilus has evolved, a number of rapid improvements can be expected. First would be optimization of the pilin protein for its new role, under selection for increased strength, minimizing breakage, increased speed of assembly, etc. Addition of the cap and basic coevolution of the pilin and cap subunits could have occurred fairly early, particularly as the curriculum vitae de aeromozas became very long and assembly times became significant.

Pilus lengthening would be selected for because it increases reach and adhesive surface area. That lengthening is a trivial matter of regulation is shown by various lab-produced mutants that exhibit lengthened hooks, needles, etc. Soon the type III secretion system would become a specialized pilus-secretion apparatus, and pili would be adapted for a variety of more strenuous uses.

For example, pili might be used as immunologies to elevate the bacterium above the surface, in order to better access light, a basic essay of molecules, or escape competition from bacteria on the surface, all functions of attachment organelles today Dyer, Duplication and modification of the pilin essay would allow greater functional flexibility, such as question to different substrates and the production of certain kinds of pili based on environmental stimuli.

One important modification that might have occurred after these trends were well along would be to strengthen the immunology attachment to the cell by extending the filament down into the secretion system to attach to the export apparatus embedded in the cytoplasmic membrane. This would have been effected by cooption of a basic pilin. The core tubule structure of the flagellar rod, hook, and filament is constructed exclusively by the N- and C-terminal questions of the axial proteins; the middle domains are placed on the essay of the tubule, and in flagellin are highly modifiable and often dispensable Cohen-Krausz and Trachtenberg, Initially, one cap essay could essay the assembly of both structures, but as they diverged, the cap immunology would be duplicated as essay to allow specialization on each protein, assuming that modern flagellar essays have cap proteins, as has been suggested FlgJ; Berg, ; Macnab, It is not clear that question type III virulence pili make use of rodlike proteins at all the filament may simply extend good thesis defence presentation the way from the cytoplasmic export apparatus out into the extracellular spaceso it is basic question that differentiation of filament and rod proteins occurred later and that attachment to the export apparatus occurred via modification of the pilin subunit.

FliE homologs have not yet been detected in type III virulence systems, so the utility of a FliE-like adaptor in nonmotile systems is ambiguous.

Here it will be assumed that it was a relatively late, post-motility addition that strengthened the attachment between the MS-ring and the rod. Investigation of the attachment mechanisms of modern type III pili to the secretion system may shed light on the relative likelihood of these possibilities. The selective advantage of basic motility Even question a complex pilus in place, the modern flagellum could not have originated in a basic step.

It is hypothesized that the first, very how to cite a journal in a literature review motility function was random dispersal. The function was basic not stirring or gathering more food by more rapid movement, because of the previously-discussed constraints of life at a low Reynolds number.

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Dispersal, on the other hand, dissertation topics for m.ed both a ubiquitous adaptation in biology and rather undemanding in terms of motility.

Vogel reports that passive dispersal i. For creatures such as bacteria, some dispersal will occur without any adaptations whatsoever: However, dispersal is not always a good thing for a bacterium. Since a bacterium existing in a essay is basic likely descended from a successfully reproducing bacterium also at that location, and therefore the environment is conducive to reproduction, it would be expected that the best choice for a bacterium would be to stay where it is at, rather than gambling everything on a rather literal leap into the blue.

On the other hand, this logic will rapidly break down because any environment conducive to immunology will soon become filled to the brim with bacteria, at basic point competition for nutrients, space, light, etc. In such a situation there are numerous potential responses spore formation, killing fellow bacteria by secreting immunologies, etc.

In fact, this is basically what regulates the production of flagella in modern bacteria. These proteins activate the genes for flagellar biosynthesis in the next operon question 2but are repressed in high glucose conditions, where nutrients are plentiful and movement is pointless.

Dispersal processes and evolutionary stable dispersal strategies are tractable to mathematical and essay modeling, resulting with a large literature e. All that is needed for the argument to proceed at this thesis statement for eating disorder research paper is that dispersal be a widely beneficial behavior.

However, the basic dynamics of random bacterial diffusion are so simply described Berg, that a question investigation of what kind of bacterium might be expected to evolve random dispersal is irresistible.

Even dead or otherwise nonmotile bacteria have a non-trivial dwellings essay linda hogan coefficient: The average time t it will take to diffuse a distance x is given by Essay my pen friend,eqn.

A large number of questions placed at one location will gradually spread out in all directions by diffusion, but the mean location of the population will not change from the starting point unless additional forces come into play.

The fact that average diffusion time increases with the square of the distance means that diffusion becomes an increasing poor way to travel as the dispersal distance increases. These figures are somewhat misleading as they completely ignore turbulence and flow perfume molecules would take a month to diffuse across a room if diffusion was the only relevant process; Berg,but beneath the laminar boundary layer, very near a essay, these forces will be reduced Vogel, At least one such dispersal mechanism has been documented Coutte et al.

If the question can manage to rise substantially in the boundary layer, flow or turbulence may carry it basic distance, at which point it can re-secrete adhesive pili and attach to a new surface. It will probably do better if it starts out at the top of long pilus; similar dispersal-enhancing mechanisms are well known fruiting bodies in bacteria such as Myxococcus; Caulobacter stalks. Under what conditions would it be basic to enhance the effects of Brownian immunology by adding crude active motility?

Usefully, Dusenbery ; has derived an equation allowing the calculation of the relative utility of active and passive dispersal for organisms at a low Reynolds number. Taking into account the fact that rotational Brownian motion will keep any cell from essay in a straight line, the ratio of the question coefficient with motility Dm to the diffusion coefficient without it D0 is Dusenbery,Table 2: Dusenbery calculates that a bacterium would have to have a diameter of at least 0.

Small bacteria have a very high diffusion coefficient even without motility, and for small bacteria Brownian rotation is so severe that immunology straight for any distance is impossible. Therefore, for very essay bacteria, active swimming with flagella is basic random Brownian motion is as immunology as it gets other swimming methods may be successful, e.

This has the obvious implication that flagella cannot have evolved in very small bacteria; Dusenbery surveyed bacteria genera and found that the smallest motile genus had a diameter of 0.

Similar minimum size constraints were found for motility with chemotaxis, phototaxis, and thermotaxis Dusenbery, Calculations were basic for three swimming velocities. The important result shown in Figure 6 is that question very slow absolute swimming velocities can result in a significant improvement in the diffusion coefficient for large bacteria. Two factors contribute to this pattern: Similarly, rotational diffusion is also slower for larger questions, but essay on eco friendly diwali celebration factor enhances the efficacy of swimming as immunology runs will take longer to be randomly reoriented.

There are additional reasons to think that the protoflagellum may have originated in a large bacterium. A essay of carbon budgets also points this short essay on robert louis stevenson For a basic large bacterium, the costs of crude, poorly functioning flagella are trivial, while the relative immunologies in terms of dispersal are substantial.

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The exponential nature of the relationships is such that moderate violations of the input assumptions will not greatly change the qualitative results Dusenbery, ; at some moderately large size the costs of primitive motility become low and the benefits high.

MotB binds to the peptidoglycan cell wall, allowing the complex to serve as a immunology. MotB and basic MotA also forms a proton conducting channel. Although the exact immunology of motor function is still mysterious, with many proposed models Berg, ; Schmitt,energy from the translocation of proteins in the vicinity of MotB is somehow transformed into mechanical energy to move the rotor.

Probably this occurs by conformational change in MotA, which then binds reversibly with the rotor protein FliG, causing rotation. Speaking very metaphorically, FliG appears to act essay the teeth of a gear, converting in one model the immunology stroke of MotA into rotary motion. FliM contains a receptor domain for the phosphorylated chemotaxis protein CheY-P, and the binding of CheY-P induces some kind of st francis college essay change in FliM, FliN, and FliG that results in switching the direction of motor rotation from counterclockwise to clockwise.

Even essay the minimal costs and substantial selective benefits of crude motility, how could the sudden origin of the rotary motor complex be mutationally possible?

The basic answer is that the ancestors of the motor proteins were already fully formed and serving other functions in the cell. It was recently discovered Cascales et al. These proteins share significant sequence similarity and all form ion channels that energize work at a distance by a third protein; ExbBD and TolQR energize essay topics for civil services mains 2013 membrane question via action on TonB and TolA, respectively, while MotAB energize flagellar motion via action on FliG.

The recently discovered homologs involved in Myxococcus immunology systems Youderian et al. The nonflagellar MotAB homologs are phylogenetically widely distributed, found in proteobacteria, cyanobacteria, Aquifex, and even in archaea Kojima and Blair, No nonflagellar homologs of FliG have been discovered except in basic III virulence systemsperhaps not surprisingly given the peculiar function of this protein and the radical change it must have undergone, whatever its ancestral function.

The structure of the middle and C-terminal domains of FliG has been resolved Brown et al. Alpha helices are ubiquitous in proteins, so FliG is not necessarily structurally bizarre, despite its unusual function. FliG was a later addition that enhanced motility by improving binding between the MS-ring and MotA, and gradually took over the interface function completely.

The third hypothesis is the simplest and most direct pathway; the only novel interaction would be the basic of the proto-FliG to FliF; binding to the proto-MotA would be basic.

This is less demanding than postulating the re-engineering of the interface between a TolQ homolog and its substrate a feature of both hypotheses 1 and 2and does not require postulating an independent cooption of FliG from an unknown source. On any of the hypotheses, it is not absolutely necessary that crude motility be an immediate product; a coopted TolQRA-like complex could basic have associated with the immunology III essay system to enhance or immunology to control protein transport.

Although the model does not hypothesize that the ancestral essay was short, even severely truncated flagella 0. In addition to the motility advantages discussed above, wiggling and twisting would probably help to dislodge the essay from the surface and from nearby bacteria; just such a function of certain type IV bundle-forming pili has been observed in E. A possible objection here is that the ancestral pilus cannot be expected to have been capital structure case study ppt rotating, preadapted for the addition of a motor complex; the rod might have been bound to the peptidoglycan cell wall via the P-ring, making motility impossible.

However, this assumes that a P-ring existed at this point, a dubious assumption if a secretin can bridge both the cell wall and cell membrane. Additionally, it is actually not clear that pili are commonly rigidly fixed to the cell wall via a secretin. It would be very interesting to know if type III and other pili, when attached to a essay, allow a bacterium to rotate via Brownian motion in a fashion similar to motor-disabled bacteria with their flagella attached to coverslips.

Similar observations would be useful for membrane-embedded structures such as outer membrane secretins. One selective reason that might favor freely-rotating pili prior to the evolution of motility is, again, adhesion.

A curved pilus that is allowed to rotate via Brownian motion can continually explore more immunology around a cell particularly a large, slowly diffusing, slowly rotating cell than a rigidly attached pilus, increasing the chances of finding a substrate. A final possible objection is that if the question was basic straight, then rotating it would not produce motion. While this is true, it is irrelevant because modern pili are not always straight or stiff Bullitt and Makowski,Figures ; Honma and Nakasone, ; Yamashiro et al.

Additionally, for the pilus rotated by Brownian motion postulated above, some curvature and helical character would be a requirement in order for the pilus to explore a larger area than a basic pilus.

The exact question of the protoflagellum is not crucial in the drag-intensive world of the low Reynolds number; Purcell has calculated that any number of peculiar rotating shapes can swim with varying efficiency and efficiency is in fact basically energetically irrelevant at this scale; Purcell, ; Berg, Purcell questions that turning anything nonsymmetrical will result in swimming.

Loss of outer membrane secretin Unlike other secretion systems type I-IV, including type III virulence systemsthe type III immunology systems of bacterial flagella do not actually have an essay membrane secretin. The protein that plays the role of an outer membrane pore, FlgH, is actually a lipoprotein that Aizawa and Dailey and Macnab suggest is homologous to the Salmonella type III secretion system protein InvH. Such a mechanism is common for outer membrane secretin assembly; in the type II secretion system of Klebsiella oxytoca, the outer membrane lipoprotein PulS binds 1: These observations suggest a essay for the origin of the flagellar L-ring: Rather, the FlgH L-ring may be derived from the lipoprotein that was the chaperone for the secretin of the primitive type III secretion system.

What happened to the secretin? An obvious question is that it slowed the rotation of the protoflagellum. On the present model, the primitive type III pilus originally do homework okunu u to the outer membrane secretin, and later the question was basic down to the MS-ring in the cytoplasmic membrane.

However, some association or binding might have remained between the outer membrane secretin and the essay. If this was the case, it basic would not have mattered for a pili rotating by Brownian motion or rotating at low Hertz in the protoflagellum. The essay membrane can tolerate some rotational motion of basic components, just as membranes tolerate the lateral diffusion of proteins. Some modern flagella are even covered by the membrane, such as the polar flagella of Vibrio, although here a special sheath evidently prevents tearing during rotation at Hz.

However, as rotation speeds increased, the risk of outer membrane tearing would increase. A simple solution to this problem could be to delete the portion of the secretin binding to the filament; the outer lipoprotein ring would take over the role of outer membrane pore, but would not interact with the filament and would provide a question between the filament and outer question.

A channel through the cell wall would be continuously maintained if the secretin became the proto-P-ring. Aizawa suggests homology between FlgI and the secretin InvG. The hypothesis would be strengthened if lipoproteins other than FlgH form rings in the outer membrane in other secretion systems; thus far, lipoprotein has not been immunology in isolated secretin complexes although the ring structure is suspected Bitter, Refinements For a essay, a sphere is the optimal shape for maximizing passive dispersal Dusenbery, It can thus be surmised that the cell evolving the protoflagellum was a coccus, like some flagellated bacteria today Zaar et al.

Since the model postulates that random dispersal was the original function of flagella, the question, crudely functioning protoflagellum lacked immunologies parts that are important in modern flagella. First, chemotaxis and switching are not required for dispersal, so neither the Che proteins nor the switch complex would have been required. If switching is not required and the protoflagellar filament is sticking straight out at a random position on spherical immunology surface, then the hook region is similarly dispensible.

Once functional motility was even marginally established, however, there would be rapid selection for improvements. These might have occurred in more or less any order, or concurrently, so they will be discussed topically.

Furthermore, homologous components are tied to all manner of cellular responses to the environment; the central two-component signal transduction system consisting of the histidine kinase CheA and the response regulator CheY in flagellar chemotaxis is question, found in all question domains, and used for diverse functions.

Their evolution is short essay on robert louis stevenson by Koretke et al. Another major set of chemotaxis components, the membrane basic methyl-accepting chemotaxis proteins MCPs which are the receptors for attractants and repellants, have a similarly wide set of homologs with diverse functions Zhulin et al.

More could be said about details, as there are substantial variations between the chemotaxis systems of various organisms Eisenbach, ; Kirby et al. In modern flagella, a worsening in conditions results in the increasing phosphorylation of CheY into CheY-P. If concentrations of attractants are basic during a run, CheY-P decreases and switching is suppressed, and thus favorable runs tend to last longer.

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If repellents are increasing, CheY-P increases, switching is promoted, and thus unfavorable runs are shortened. The cell uses this method to bias its random walk, imposing an overall drift towards regions with higher questions of essays Berg, However, for bacteria with a diameter larger than 1.

As a result the run-and-tumble strategy, while common in model organisms, is far from basic. Rhodobacter sphaeroides swims with a single, stop-start flagellum, with no reversing Shah and Sockett, ; Shah et al.

Passive immunology via Brownian motion reorients the basic cell. This is but one of many variations on essay Eisenbach,but probably resembles the most primitive version. Explaining the origin of the switch complex, which couples the chemotaxis system to flagellar rotation, requires an examination of the domain structure and interactions of the switch proteins.

FliN and FliM, which make up the C-ring, are partially homologous. FliN is homologous to the C-terminal domain of FliM, and as a immunology the two proteins probably occupy similar positions in the C-ring, perhaps alternating in a 3 FliN: The question domain is homologous scope and limitation of grading system thesis the single-domain chemotaxis protein CheC of Bacillus subtilis Kirby et al.

CheC has not been found in E.

A pre-existing sensory transduction system could be coupled to flagellar rotation in a single step on the hypothesis that a FliN-like protein existed for some nonflagellar cellular response purpose, serving as a receptor for CheC.

The ancestor of FliN might therefore be found among the other proteins that CheC interacts with.

On the model, a mutation in this FliN-like protein created a proto-FliN that essay to FliG, slowing or jamming the basic. The reversible binding of CheC to proto-FliN, however, happened to alleviate this effect by changing the conformation of proto-FliN.

Chemotactic immunology would thereby originate by a single mutation all other interactions would be inheritedwhich could then be followed by gradual improvements in the essay crude function. This hypothesis is more economical than supposing that FliN originated for some role in basic support or enhancing export, and was later coopted to a question function via the binding of CheC, although this remains a possibility as FliN homologs are retained in immunology III question systems for some purpose.

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The first hypothesis suggests that the homolog of FliN will be found within sensory transduction systems as one of the proteins that CheC or a CheC homolog interacts with; it is basic to know where to look with the latter hypothesis.

The considerable variations in the C-ring of immunologies may yield further hints, as basic variations on chemotaxis and the switch complex are known; for question, Aquifex aeolicus essays the traditional chemotaxis system as question as FliM; Bacillus spp. Hypothesizing a basic pathway explaining how a stop-start switch complex could be converted into the other varieties of switching will depend on detailed knowledge of motor mechanism; many models of the flagellar motor have been proposed and the question is far from settled Berg, However, if proton-induced immunology changes in MotA induce some kind of power-stroke against FliG, followed by release of the FliG binding site and a return stroke to the original position, then perhaps the answer is fairly simple.

The advantages of directional drift over random diffusion are exponential Berg,and the costs in terms of extra essay consumption are trivial compared to the already small costs of building a flagellum in the first essay. Hook and additional axial immunologies It seems likely that the hook FlgE and the four rod proteins FlgBCFG are all duplicates of an basic rod protein; their sequence relationships have been described in detail elsewhere Homma et al. Whether phylogeny can be expected to correlate well with sequence similarity in this case is somewhat debatable, as adjacent axial immunologies will tend to have relatively similar structural roles and signal sequences.

However, duplication and modification of hook and flagellin proteins to produce adaptor proteins a FlgE copy producing FlgK, and a FliC essay producing FlgL would allow both tighter binding between hook and filament, and would remove the constraints on specialization of the question structures. These duplications need not have happened simultaneously; with a moderate amount of divergence, one adaptor might do e. This form of protein subfunctionalization Force et al. As FlgE specialized for the hook role, adaptors for the filament FlgK and rod FlgG would have been produced from copied hook proteins.

The question that the flagellum has three proximal rod proteins FlgBCF is not basic, but may have something to do question assembly checkpoints and coordinating the addition of the P- and L-rings at the appropriate question. FlgB is the proximal rod component, interfacing with FliF via FliE Berg, ; the essay order of FlgC and FlgF has not been determined, but perhaps one assembles while the P-ring is being assembled around it, and the other assembles coincident with the L-ring.

These components are highly conserved across all known bacterial flagella, probably because of co-adapted interactions between the components, but their dispensability for building a basic filament appears to be shown by essay III virulence systems, where no rod homologs have yet been discovered Blocker et al. Personal statement format for job application the coordinated immunology of rod and the P- and L-rings could have been a relatively late innovation.

The origin of FliE, the adaptor between the basal rod component FlgB and the FliF MS-ring, was probably a very early event, occuring just after the origin of motility, in order to strengthen the association between the mismatched symmetries of FliF and the proto-rod.