#protofilament

[whats-in-a-sentence]

These γ-tubulin ring complexes are present in the cortical cytoplasm, sometimes associated with the microtubule branches (Figure 1.26A-C), similar to how Arp 2/3 is present at branches of microfilaments. (...) Next, the protofilaments (the number varies with species) associate laterally to form a flat sheet (see Figure 1.26A). The sheet curls into a cylindrical microtubule as GTP is hydrolyzed (see Figure 1.26B). (...) The hydrolysis of GTP to GDP on the β-tubulin subunit causes the dimer to bend slightly, and if the rate of GTP hydrolysis "catches up" with the rate of addition of new heterodimers, the GTP-charged cap of tubulin vanishes and the protofilaments come apart from each other, initiating a catastrophic depolymerization that is much more rapid than the rate of polymerization (see Figure 1.26C). (...) This process is called dynamic instability (see Figure 1.26A-C).

However, plant microtubules can be released from γ-tubulin ring complexes by an ATPase, katanin (from the Japanese word katana, "samurai sword"), which severs the microtubule at the point where the growing microtubule branches off another (see Figure 1.26D). (...) During treadmilling, tubulin heterodimers are added to the growing plus end at about the same rate that they are removed from the shrinking minus end (see Figure 1.26D). The actual tubulin subunits do not move relative to the cell once they are polymerized into the microtubule (see shaded region in Figure 1.26D), because the microtubule is usually bound to a membrane through a variety of MAPs.

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[doompunkdispatch]

Feast on God’s Flesh

Hard-hitting junkies went missing soon after the Pharmacyst came to town. Rumor was they went to live fulltime in his bunker, completing the irreversible metamorphosis enforced by his eldritch substances.

A small dose doesn’t enact a noticeable difference, so you wouldn’t fear having a second hit, then a third. Something stronger than addiction takes hold. The user’s biochemistry transmogrifies into impossible directions. Eye-drops distend the iris. Inhaled smoke colonizes the bronchioles. Liquid injections taint the blood. Snort the powder and feel its crystals vivisect your gray matter, opening up wounds for infection by a macroscopic foe.

See them now. Sink past dreariest dungeons and discern the gruesome machinations: organs harvested from twisted junky cadavers, hormones siphoned to synthesize new compounds for fresh generations of victims. Sallow survivors wander aimless corridors until their time arrives. At the behest of the Pharmacyst, ghoulish orderlies squeeze jellied brains into pillcaps, sieve amber pus into hypodermic needles, and crush bone into dust to cut with cocaine—the customers may be right, but they never know any better.

You spot skin, hard as petrified bark. Fauna gives birth to flora and fungi. Three bodies hang from ceiling hooks, intertwined via splintered twig arms. Leaves and flowers, reeking of odious rot, unfold between their fingers. Mushroom caps sprout from gnarled toenails, ripe for the plucking.

An undercooked fetus elongates into a symbiotic vine, enwrapping its parents’ trunks. The perverse family unit bears physical fruit; a jaundiced mesocarp drips sweet juices from splitting tumescent flesh. One subject tastes this pome, and feels a figwasp ovum rapidly developing in her belly. Parasitic visitors from innermost realms burst into our sliver of reality, celebrating the open-ended orgy that is All Creation.

Near the bottom, we find a ward housing xeno-amphibious forms, formerly human. The transfiguration left them with skin akin to earthly frogs. This gelatinous surface breathes Earth’s air, metabolizes various gasses, and secretes fluid coveted by only the most perverse addicts. Emitting froglike croaks, the tsathögguans must be kept in tanks tuned to binaural beats. Any naked eardrum that absorbs its vibration begins transmuting the surrounding skin to an exogenetic structure matching the source. Word is Virus.

Things get darker. Woven cocoons quiver in the grimiest guts of the citadel. Furtive nostrils ponder our astral scent as we pass their cells. Chitinous hairs chitter in anticipation of a meal. Curious third eyes gaze brightly from the tips of protuberant pineal glands. Slavering mandibles lunge out—

—and snatch you from the metafictional air.

Digestive enzymes pull apart the essential cogs of your mental machinery. Vicious biochemical troops rip through protofilaments and pillage delicious proteins from your doomed neurons. Curious stomachs digest juice sickly rich in consciousness. You feel yourself melt into them. Ovipositors plant eukaryotic yolks between your sulci and gyri. Your undiscovered carcass will sustain families for generations to come. Great-grandchildren will chew on your flickering subliminal sewage. Slurp up scumpunk soup.

“Open wide,” smiles the Pharmacyst, “and swallow your medicine.”

[cytgen]

Abstract The analysis of the effect of ivermectin on phytopathogenic strains of Fusarium graminearum (F‑55644, F-55748) and Fusarium oxysporum f. sp. lycopersici (F-52897, F-55547) was carried out; as a result, its concentrations were established at which a fungistatic effect on the growth of colonies of the specified strains was observed (2 and 3 mg/mL). It was found that F. oxysporum strains were more susceptible in general to ivermectin than F. graminearum strains. Since it is known that ivermectin is able to interact with β-tubulin (causing a stabilization of microtubules), to explain the obtained results, a 3-dimensional model of the complex of this compound with Fusarium β-tubulin was developed and ivermectin-induced changes in the conformation of β-tubulin were determined, including, particularly, the stabilization and spiralization of the M‑loop of the β-tubulin molecule. This structural element of β-tubulin plays an important role in the lateral contacts between tubulin subunits of adjacent protofilaments within the microtubule. Since the M-loop stabilization reflects a very important feature of microtubule stabilizing agents' binding to the taxane site of β-tubulin, it can be supposed, that ivermectin possesses the same effect on Fusarium microtubules. The results obtained allow for considering ivermectin or its derivatives as potential compounds with fungicidal activity.

[artistlove]

Cytosquelette :

Le cytosquelette est un réseau de filaments protéinés qui confère sa forme, l'organisation interne et son déplacement.

Les composants du cytosquelette sont renouvelés en permanence par polymérisation, le cytosquelette est à l'origine des déplacements de la cellule pour se nourrir ressemblant comme à des muscles.

Il permet aussi de les différencier entre cellule car leur structure est différent entre Eucaryotes et Procaryotes.

Les propriétés du cytosquelette varie en fonction des comportements et des situations.

Il y as plusieurs type de filaments :

Microtubules (MT)

Des fibres continuel du cytosquelette au même titre que les microfilaments d'actine et les filaments intermédiaire.

Leur longueur est considérablement variable étant donné la polymérisation et la dépolymérisation constante.

Il es ancré dans le centrosome et impliqué dans la mitose où le longueur variable joue un rôle.

Les microtubules son formés de dimères et de tubulines, chacun constitué de deux sous-unités, la tubuline a et la tubuline b liées par des liaisons non covalentes.

Les dimères s'assemble pour formé les protofilament qui constitue la paroi du microtubule dont l'intérieur semble vide.

Les dimères de tubuline et l'orientation est polarisé le long de chaque protofilament, un côté ne comportent que des tubuline b, et une autre de tubuline a.

Cet assemblage est toujours en action, elle polymerisent et depolymerisent constamment.

In vivo comme in vitro, on peut observer des effondrements rapides ou, au contraire, la stabilisation des microtubules.

Dimères

C'est une molécule de la famille des polymères qui ne comporte que deux sous-unités.

Par exemple le sucre : le saccharose est un dimère qui réunit le glucose et le fructose.

Un dimères sont deux molécule de structure similaires sont fortement rapproché mais sans formé de liaison chimique.

En biologie, c'est un complexe de protéines qui compose deux sous-unités, identiques pour un homodimère et différentes pour un heterodimère.

Les sous-unités n'ont pas besoin d'être liées de façon covalentes et ne le sont généralement pas.

Un dimères peut aussi être constitué de deux bases nucléiques sur un même brin reliées par une double liaison et inhibe les ADN polymérases.

La tubuline dirige la dynamique des microtubules, suivant sa concentration dans la cellule, elle va diriger la polymérisation ou la dépolymérisation.

Si la tubuline-GTP est concentré, les dimères a-b se polymérisent forment les protofilament. Puit il s'associent pour former le microtubule.

L'assemblage de protofilament peut conduire à l'obtention d'un flagelle.

Si la tubuline-GTP n'est pas assez concentré, les protofilament vont de dépolymérisé et se dégrader.

Les microtubules chez les eucaryotes on une structure cytosolique qui rayonnent appelée centrosome.

Les cellules végétales, possèdent une autre structure, non visible, appelée « centre organisateur des microtubules ».

Tubuline a

Tubuline b

La tubuline est une protéine structurales des microtubules, constituant majeur du cytosquelette.

Elle a une masse moléculaire d'environ 100 kDa.

La tubuline a et b sont en faite très semblable et ne diffère que de quelque acides aminés.

Elle est composée de 2 sous-unités non identiques :

La tubuline a : Elle as une masse moléculaire d'environ 50kDa et à un pHI de 5,3-5,8 et est liée au GTP.

La tubuline β : Elle as une masse moléculaire d'environ 50kDa et à un pHI de l'ordre de 5,3-5,6 et est liée au GTP, où elle à la capacité d'hydrolyser.

C'est l'état de cette sous-unité qui définit l'état « GTP » ou « GDP » de la tubuline.

Polymérisation :

Il y a trois phases dans la polymérisation des dimères de tubuline menant au microtubules :

Phase de nucléation :

Consiste à l'assemblage des hétérodimeres a et b de tubuline concomitant à l'hydrolyse de la GTP catalysée par la sous-unités b.

Elle constitue la base sur laquelle le microtubule croît.

Retard :

Pendant l'élongation le microtubule croît que l'hydrolyse du GTP est retardée par rapport au dimères de tubuline dans le microtubules.

In vitro, in Vivo :

In vitro, les dimères se lient au deux extrémités du microtubule bien qu'elle soit plus rapide à l'extrémité+.

In Vivo, l'extrémité - du microtubule est stabilisé pour être lié au centrosome.

La langueur de microtubules est constante alors que l'élongation et l'effondrement ont des vitesse égale.

Les microtubules sont susceptibles de s'effondrer totalement sur eux-mêmes, in vitro comme in vivo.

[nuadox]

Novel wool-like material can remember and alter shape

- By Leah Burrows , Harvard John A. Paulson School Of Engineering And Applied Sciences -

As anyone who has ever straightened their hair knows, water is the enemy. Hair painstakingly straightened by heat will bounce back into curls the minute it touches water. Why? Because hair has shape memory. Its material properties allow it to change shape in response to certain stimuli and return to its original shape in response to others.

Video: “Wool-like material can remember and change shape” by Harvard John A. Paulson School of Engineering and Applied Sciences, YouTube.

What if other materials, especially textiles, had this type of shape memory? Imagine a t-shirt with cooling vents that opened when exposed to moisture and closed when dry, or one-size-fits-all clothing that stretches or shrinks to a person’s measurements.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a biocompatible material that can be 3D-printed into any shape and pre-programmed with reversible shape memory. The material is made using keratin, a fibrous protein found in hair, nails and shells. The researchers extracted the keratin from leftover Agora wool used in textile manufacturing.

The research could help the broader effort of reducing waste in the fashion industry, one of the biggest polluters on the planet. Already, designers such as  Stella McCartney are reimagining how the industry uses materials, including wool.

"With this project, we have shown that not only can we recycle wool but we can build things out of the recycled wool that have never been imagined before,” said Kit Parker, the Tarr Family Professor of Bioengineering and Applied Physics at SEAS and senior author of the paper. “The implications for the sustainability of natural resources are clear. With recycled keratin protein, we can do just as much, or more, than what has been done by shearing animals to date and, in doing so, reduce the environmental impact of the textile and fashion industry.”

The research is published in Nature Materials.

The key to keratin’s shape-changing abilities is its hierarchical structure, said Luca Cera, a postdoctoral fellow at SEAS and first author of the paper.

A single chain of keratin is arranged into a spring-like structure known as alpha-helix. Two of these chains twist together to form a structure known as a coiled coil. Many of these coiled coils are assembled into protofilaments and eventually large fibers.

“The organization of the alpha helix and the connective chemical bonds give the material both strength and shape memory,” said Cera.

When a fiber is stretched or exposed to a particular stimulus, the spring-like structures uncoil, and the bonds realign to form stable beta-sheets. The fiber remains in that position until it is triggered to coil back into its original shape.

To demonstrate this process, the researchers 3D-printed keratin sheets in a variety of shapes. They programmed the material’s permanent shape — the shape it will always return to when triggered — using a solution of hydrogen peroxide and monosodium phosphate.

Once the memory was set, the sheet could be re-programmed and molded into new shapes.

For example, one keratin sheet was folded into a complex origami star as its permanent shape. Once the memory was set, the researchers dunked the star in water, where it unfolded and became malleable. From there, they rolled the sheet into a tight tube. Once dry, the sheet was locked in as a fully stable and functional tube. To reverse the process, they put the tube back into water, where it unrolled and folded back into an origami star.

Motion graphic: A keratin sheet folded into a complex origami star as its permanent shape. Once the memory was set, the researchers dunked the star in water, where it unfolded and became malleable. From there, they rolled the sheet into a tight tube. Once dry, the sheet was locked in as a fully stable and functional tube. To reverse the process, they put the tube back into water, where it unrolled and folded back into an origami star. Credit: Luca Cera/Harvard SEAS.

“This two-step process of 3D printing the material and then setting its permanent shapes allows for the fabrication of really complex shapes with structural features down to the micron level,” said Cera. “This makes the material suitable for a vast range of applications from textile to tissue engineering.”

"Whether you are using fibers like this to make brassieres whose cup size and shape can be customized every day, or you are trying to make actuating textiles for medical therapeutics, the possibilities of Luca's work are broad and exciting,” said Parker. “We are continuing to reimagine textiles by using biological molecules as engineering substrates like they have never been used before."

--

Source: Harvard John A. Paulson School of Engineering and Applied Sciences

Full study: “A bioinspired and hierarchically structured shape-memory material”, Nature Materials.

http://dx.doi.org/10.1038/s41563-020-0789-2

Read Also

Laser inversion could potentially enable multi-materials 3D printing

[jhavelikes]

Consistent with its early onset phenotype in patients, Asp23Asn accelerates aggregation of Aβ 20–34, as does the L-isoAsp23 modification. These structures suggest that the enhanced amyloidogenicity of the modified Aβ segments may also reduce the concentration required to achieve nucleation and therefore help spur the pathogenesis of AD.

Structure of amyloid-β (20-34) with Alzheimer’s-associated isomerization at Asp23 reveals a distinct protofilament interface | Nature Communications

[sbgridconsortium]

Structure and Stability

Microtubules are important cell components involved in motility and division. These structures are formed by the assembly of protofilaments composed of αβ-tubulin heterodimers. Since the structure and function of microtubules can be influenced by post-translational modifications of tubulin, it is important to understand the effects of post-translational modifications on microtubule stability and behavior. Previous work has suggested that an α-tubulin post-translational modification, K40 acetylation on the luminal surface of the microtubule, enhances microtubule half-life in cilia and flagella. However, since the structural basis for this potential stabilization remained unknown, it was unclear whether K40 acetylation of α-tubulin caused or was simply correlated with enhanced α-tubulin stability. An improved understanding of how this post-translational modification impacts α-tubulin stability is clinically important because associations have been reported between reduced K40 acetylation and axonal transport defects linked to diseases including Huntington’s disease, Charcot-Marie-Tooth, amyotrophic lateral sclerosis (ALS), and Parkinson’s disease.

Above: Polymerization of microtubules through the formation of αβ-tubulin heterodimers. The acetylation of K40 in α-tubulin may promote microtubulin stability. CC BY SBGrid.

SBGrid members Eva Nogales and James Fraser along with other researchers have been working to study the structural effects of K40 post-translational modification of α-tubulin. They applied high-resolution cryo-electron microscopy and molecular dynamics simulations to acetylated and deacetylated microtubules to investigate this. Interestingly, they found that the acetylation of K40 in α-tubulin reduced the range of motion and conformational states of the corresponding αK40 loop in which the post-translational modification occurs. Based on these findings, the authors suggest that the acetylation of K40 in α-tubulin is likely to influence microtubule stability and potential lateral contacts within the microtubule structure.

Read more about this work in PNAS.

[celluloyd]

Microtubule et GTP

Le microtubule est un multimère de tubulines - de type alpha (α) ou beta (β) - formée de plusieurs protofilaments enroulés en un tube creux. Sur le schéma il est vu de dessus à son extrémité libre dite (+), par opposition à l'autre extrémité enchâssée dans le centrosome. Les protofilaments terminent à leur extrémité (+) par une tubuline β.

Le guanosine tri-phosphate (GTP) est fixé sur les tubulines des microtubules, et s'il est hydrolysé en guanosine di-phosphate (GDP) alors la tubuline n'est plus stable et s'en va du microtubule : ce dernier se dé-polymérise. Pour les tubulines α le GTP est à l'intérieur du microtubule, alors que pour les tubulines β le GTP est à l'extérieur. Ainsi le GTP des tubulines α est inaccessible par les hydrolases du GTP et autres facteurs de régulation, alors qu'il est accessible sur les tubulines β : c'est cette dernière qui est donc la cible de la régulation des microtubules généralement.

Ces schémas ont été faits pour mes ED du Tutorat à partir des cours que j'ai retranscrit quand j'étais en première année de médecine. Ma seule source est le professeur de l'époque, et je peux avoir mal compris certaines choses, faire des approximations fausses, etc même si je fais de mon mieux. Croiser les sources permet d'avoir des informations plus fiables. N'hésitez pas à commenter pour discuter des sujets abordés ! Schémas et explications faits entre 2015 et 2016.

[scienceblogtumbler]

Imagine clothing that stretches or shrinks to fit you

As everyone who has painstakingly straightened their hair knows, water is the enemy. Hair carefully straightened by heat will bounce back into curls the minute it touches water. Why? Because hair has shape memory. Its material properties allow it to change shape in response to certain stimuli and return to its original shape in response to others.

What if other materials, especially textiles, had this type of shape memory? Imagine a T-shirt with cooling vents that opened when exposed to moisture and closed when dry, or one-size-fits-all clothing that stretches or shrinks to a person’s measurements.

Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a biocompatible material that can be 3D-printed into any shape and pre-programmed with reversible shape memory. The material is made using keratin, a fibrous protein found in hair, nails, and shells. The researchers extracted the keratin from leftover Agora wool used in textile manufacturing.

The research could help the effort to reduce waste in the fashion industry, one of the biggest polluters on the planet. Already, designers such as Stella McCarthy are reimagining how the industry uses materials, including wool. The material may also have medical uses.

“With this project, we have shown that not only can we recycle wool but we can build things out of the recycled wool that have never been imagined before,” said Kit Parker, the Tarr Family Professor of Bioengineering and Applied Physics at SEAS and senior author of the paper on the subject published in Nature Materials. “The implications for the sustainability of natural resources are clear. With recycled keratin protein, we can do just as much, or more, than what has been done by shearing animals to date and, in doing so, reduce the environmental impact of the textile and fashion industry.”

The key to keratin’s shape-changing abilities is its hierarchical structure, said Luca Cera, a postdoctoral fellow at SEAS and first author of the paper. A single chain of keratin is arranged into a spring-like structure known as alpha-helix. Two of these chains twist together to form a structure known as a coiled coil. Many of these are assembled into protofilaments and eventually large fibers.

“The organization of the alpha helix and the connective chemical bonds give the material both strength and shape memory,” said Cera.

When a fiber is stretched or exposed to a particular stimulus, the spring-like structures uncoil, and the bonds realign to form stable beta-sheets. The fiber remains in that position until it is triggered to coil back into its original shape.

To demonstrate this process, the researchers 3D-printed keratin sheets in a variety of shapes. They programmed the material’s permanent shape — which it will always return to when triggered — using a solution of hydrogen peroxide and monosodium phosphate. Once the memory was set, the sheet could be re-programmed and molded into new shapes.

For example, one keratin sheet was folded into a complex origami star as its permanent shape. Once the memory was set, the researchers dunked the star in water, where it unfolded and became malleable. From there, they rolled the sheet into a tight tube. Once dry, the sheet was locked in as a fully stable and functional tube. To reverse the process, they put the tube back into water, where it unrolled and folded back into an origami star.

“This two-step process of 3D printing the material and then setting its permanent shapes allows for the fabrication of really complex shapes with structural features down to the micron level,” said Cera. “This makes the material suitable for a vast range of applications from textile to tissue engineering.”

“Whether you are using fibers like this to make brassieres whose cup size and shape can be customized every day, or you are trying to make actuating textiles for medical therapeutics, the possibilities of Luca’s work are broad and exciting,” said Parker. “We are continuing to reimagine textiles by using biological molecules as engineering substrates like they have never been used before.”

 This research is co-authored by Grant Gonzalez, Qihan Liu, Suji Choi, Christophe Chantre, Juncheol Lee, Rudy Gabardi, Myung Choi, and Kwanwoo Shin.

It was supported in part by the Harvard University Materials Research Science and Engineering Center (MRSEC), under grant DMR-1420570 from the Nation Science Foundation.

source https://scienceblog.com/518373/imagine-clothing-that-stretches-or-shrinks-to-fit-you/

[malbertivalls-blog]

Biocel resums: Tema 7.

El citoesquelet de tubulina:

El citoesquelet de tubulina està format per blocs bàsics dimèrics de alfa i beta tubulina. Són homòlegs gairebé indèntics que troben les seves diferències en la capcitat del beta d’hidrolitzar el seu gtp. La unió d’unn nombre indefinit de dímers crearà un protofilament, que alhora, quan s’uneixi amb 12 protofilaments més (13) crearà un microtúbul. Poden crear dímers de túbuls i en aquests casos compartiran protofilaments 13+10+10, per exemple.

La cinètica també em fa pal explicar-la, és la mateixa, amb el detall de els caps de GTP i les catastrofes i rescats.

D’on neixen? Tot i que també poden nèixer d’altres punts com axonemes, principalment sortiran de MTOC, centres organitzadors de microtubuls.Auqests centres estan creats a oartir de 9 triples de alfa + beta+ delta tubulina amb una llum repleta de gamma-tubulina (proteïna activada amb un residu de tirosina). Com va doncs la creació. Resulta que aquest MTOC crea unes estructures anomades gamma-TuRC que són dos gamma tubulines i proteïnes accessòries. La forma d’espiral d’aquest grup permet agrupar protofilaments de manera discontinua. S’ajunten 7 gamma-TuRC per a fer un microtubul.

La síntesis i ensamblatge no ha de ser necessàriament un procés que vagi d’una tirada, podem enssamblar els tubuls en diferents punts després de ja haver-los sintetizat. 

[yeast-papers]

Microtubules grow by the addition of bent guanosine triphosphate tubulin to the tips of curved protofilaments.

Pubmed: http://dlvr.it/R8Zb63

[zaynclinic]

Hair Transplant

Hair cosmetics are an important tool that helps to increase patient's adhesion to alopecia and scalp treatments. This article reviews the formulations and the mode of action of hair cosmetics: Shampoos, conditioners, hair straightening products, hair dyes and henna; regarding their prescription and safetiness. The dermatologist's knowledge of hair care products, their use, and their possible side effects can extend to an understanding of cosmetic resources and help dermatologists to better treat hair and scalp conditions according to the diversity of hair types and ethnicity.

Keywords: Hair, hair care, hair cosmetics

INTRODUCTION Although dermatologists are experts in managing scalp and hair diseases, the esthetic of some cosmetic therapies still remain elusive. Knowledge of hair cosmetics and esthetic procedures as well as of the hair shaft structure and physical behavior is indeed relevant in today's medical practice.Although hair cosmetics are widely available, the medical literature is rather scarce, and specialized literature is not readily accessible. The aim of this chapter is to allow a better understanding of the hair shaft structure and behavior, as well as information about the hair cosmetics. Knowing their mode of action, safetiness and ingredients will enable the physician to better assess different problems secondary to cosmetic treatments. Cosmetic hair care procedures are mostly used by descendent women, whose hair fragility has been related to be worsen by hair care practices. According to hair fragility leading to breakage can occur due to genetic predisposition, weathering from various hair care practices. Hispanic patients also have curly or very curly hair that may clinically behave as sensitive as African hair when exposed to hair care procedures. Although scientific data is lacking to prove whether Hispanic hair is really as sensitive, it is common to see Hispanic women with chemically straightened hair, suffering from hair breakage and asking for the dermatologist help and advice to overcome the problem. Also, it is important to distinguish hair shed due to telogen effluvium from hair shed due to hair shaft breakage, which is not always clear from the patient point of view.

HAIR Hair is an integrated system with a peculiar chemical and physical behavior. It is a complex structure of several morphological components that act as a unit. The hair shaft of mammals is divided into three main regions: Cuticle, cortex and medulla. The medulla is present in corser hair like grey hair, thick hair and beard hair, and it is absent in fine hair of children. There is more medulla in the coarser hair of Asians than Caucasians. The medulla may be involved in the splitting of hairs since it provides an area of weakness as a pathway for the propagation of cracks along the axis of the fiber.

The cuticle is a chemically resistant region and consists of flap overlapping scales (keratinocytes) like shingles on the roof. The shape and orientation of the cuticle cells are responsible for the differential friction effect in hair. The cuticle is generally formed by 6–8 scales thick for Asians, slightly less in Caucasians and even less in African hair. A thinner cuticle layer makes African hair more prone to breakage. Each cuticle cell contains a thin proteinaceous membrane, the epicuticle, covered with a lipid layer that includes the 18-methyl eicosanoic acid (18-MEA) and free lipids. Beneath the cuticle cells membranes there are three layers, all containing heavily cross-linked protein, mostly cystine, the A-layer, the exocuticle or B-layer and the endocuticle. The first one contains the higher amount of cystine, and the third one contains the lowest. The 18-MEA is responsible for the hydrophobicity of the hair and its removal by alkaline chemical cosmetics procedures may damage hair by increasing hydrophilia.

The cell membrane complex (CMC) is intercellular matter. CMC consists of cell membranes and adhesive material (cement) binding the cell membranes between two cuticle cells, two cortical cells and cuticle-cortex cells. The most important layer of the CMC is called the beta-layer, and it is considered to be the intercellular cement and it is sandwiched by other layers from each cell. The CMC and the endocuticle are very vulnerable regions to the chemical treatments such as bleaching, dyeing and hair straightening/perm procedures. Also, the everyday grooming and shampooing friction may disrupt the CMC.

CMC fractures may be seen before the hair fiber is ruptured. The exposure to repeated rough washing, hair transplant in pune unprotected drying, friction actions, sunlight and alkaline chemical treatments lead to a decrease in the lipid content of the cell surface changing it from the state of hydrophobicity to a more hydrophilic, negatively charged surface.

The cortex constitutes the major part of the mass of the human hair, and it is formed by elongated, hair transplant clinic in pune fusiform cells connected by a CMC and contains protein and melanin granules. The cortex cell also contains spindle-shaped fibrous structures called macrofibrils, each one consists of microfibrils that are highly organized fibrilar units and matrix. The matrix is formed by crystalline protein of high cystine content. The macrofibrils are arranged in a spiral formation. Inside the microfibrils there are subfilamentous units called protofilaments, each contains short sections of alpha-helical proteins in coiled coil formation polypeptide chains of proteins. hair treatment in pune The alpha-helix is held coiled by chemical forces such as: Ionic forces, hidrogene bonds, Van de Waal forces and disulfide bonds. Hair straightening process consists on breaking the forces that hold the coil, allowing it to be stretched. If the rupture of the chemical bonds is followed by curling the hair, it is called “perm,” meaning permanent curling. The process of reduction the hair involves hair swelling and very alkaline substances such as sodium or lithium hydroxide, guanidine, ammonium thioglicolate, pH higher than 9.0. All this can produce splits or cracks to the endocuticle and the CMC, but the major damage to hair after using hair reducing products is indeed due to misuse of the products and lack of care during combing hair in the reduced state. Hair damage caused by the use of chemical procedures can be minimized, avoided or repaired by the correct use of hair care products. Hair cosmetics may enhance hair hydrophobicity, strengthen the cuticle and minimize

[scitechman]

Dynamics of Microtubules

Cells possess an internal skeleton, which enables them to alter their form and actively migrate. This ‘cytoskeleton’ is composed of a number of filament systems, of which microtubules are one. As the name suggests, a microtubule is a cylinder. Its wall is made up of 13 protofilaments, each consisting of heterodimeric subunits containing two related tubulin proteins. Microtubules not only confer…

[artistlove]

🗒️💬

Les microtubules sont assemblés à partir de dimères d'α- et de β-tubuline. Ces sous-unités sont légèrement acides, avec un point isoélectrique compris entre 5,2 et 5,8[2]. Chacune a un poids moléculaire d'environ 50 kDa[3].

Pour former les microtubules, les dimères d'α- et de β-tubuline se lient au GTP et s'assemblent sur les extrémités (+) des microtubules lorsqu'ils sont à l'état lié au GTP[4]. La sous-unité de β-tubuline est exposée sur l'extrémité plus du microtubule, tandis que la sous-unité d'α-tubuline est exposée sur l'extrémité moins. Après l'incorporation du dimère dans le microtubule, la molécule de GTP liée à la sous-unité β-tubuline finit par s'hydrolyser en GDP par le biais de contacts interdimères le long du protofilament du microtubule[5]. La molécule de GTP liée à la sous-unité α-tubuline n'est pas hydrolysée pendant tout le processus. Le fait que le membre β-tubuline du dimère de tubuline soit lié au GTP ou au GDP influence la stabilité du dimère dans le microtubule. Les dimères liés au GTP ont tendance à s'assembler en microtubules, tandis que les dimères liés au GDP ont tendance à se désagréger ; ce cycle du GTP est donc essentiel pour l'instabilité dynamique du microtubule.

Microtubules bactériens

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Des homologues de l'α- et de la β-tubuline ont été identifiés dans le genre de bactéries Prosthecobacter[6]. Ils sont désignés BtubA et BtubB pour les identifier comme des tubulines bactériennes. Toutes deux présentent une homologie avec les α- et β-tubulines[7]. Bien que leur structure soit très similaire à celle des tubulines eucaryotes, elles présentent plusieurs caractéristiques uniques, notamment un repliement sans chaperon et une faible dimérisation[8]. Des études in vitro montrent que les BtubA/B forment des « mini-microtubules » à quatre brins[9], contrairement aux microtubules eucaryotes, qui en contiennent généralement 13.

La tubuline possède 3 sites de liaison, qui sont les cibles de médicaments anticancéreux ; le site du Taxol, de la Vinblastine et de la colchicine. La colchicine et la Vinblastine se lient à la tubuline et inhibent sa polymérisation, c'est-à-dire la formation de microtubules, immobilisant les neutrophiles et abaissant l'inflammation. Le Taxol inhibe la dépolymérisation des microtubules.

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Centrosome

Le centre organisateur des microtubules, abrégé COMT ou MTOC, est une structure présente dans les cellules eucaryotes d'où émergent les microtubules. Dans les cellules animales, il est composé de matériel péricentriolaire et d'un centrosome, lui-même composé de deux centrioles.

Dans les cellules animales, le centre organisateur des microtubules est composé d'un centrosome, organite non membrané qui se compose d'une paire de centrioles, et d'un nuage de matériel amorphe appelé matériel péricentriolaire[1]. Un centriole est composé de neuf triplets de microtubules (avec treize protofilaments entre chaque microtubule), formant la paroi d'un cylindre. C'est à partir de cet ensemble que s'effectue la nucléation des microtubules grâce à la présence, à sa surface, d'anneaux de tubuline γ, homologue de la protéine ARP pour l'actine. Il n'existe pas de continuité entre les centrioles et les microtubules cytosoliques, qui polymérisent autour des anneaux de tubuline γ. Les microtubules polymérisent à partir de ce centre organisateur qui représente le point de ralliement des microtubules, lui donnant alors un rôle primordial dans le trafic intracellulaire. Le centre organisateur des microtubules a un rôle dans l'orientation des cellules et est à l'origine des cils et des flagelles.

Durant l'interphase, le centrosome est responsable de la nucléation microtubulaire. Le centrosome se duplique au cours de la phase de synthèse (pendant l'interphase) et, pendant la mitose, se sépare pour former les deux pôles du fuseau mitotique (appareil mitotique). Il y a donc deux paires de centrioles appelées chacune « diplosome », c'est de ces deux pôles que seront nucléés les microtubules du fuseau mitotique.

Dans les cellules végétales, il n'y a pas de centrosome, mais le gamma-tubulin ring complex y est conservé et permet la nucléation de nouveaux microtubules. Cette nucléation est microtubules dépendante, c'est-à-dire qu'elle a lieu le long de microtubules déjà existants. En absence de centrosome et de centriole, dans les cellules végétales on parle généralement d'un centre organisateur de microtubule diffus. L'absence de centrosome n’empêche pas la division cellulaire d'avoir lieu, les cellules végétales ne sont d'ailleurs pas les seules à ne pas avoir de centrosome, les ovocytes en sont également dépourvus, lors de la division les pôles du fuseau sont simplement moins focalisés[2].

Les levures ne possèdent pas de centrosome, mais ont un centre organisateur des microtubules, situé en périphérie du noyau, mais aussi le long de microtubules déjà existants, cette structure est à la base de la formation des microtubules[3].

Les neurones n'ont pas de centrosome.

Les cellules cancéreuses contiennent un ou plusieurs centrosomes supplémentaires, mais peuvent néanmoins se reproduire. Ceci est une caractéristique propre, connue depuis le début du xxe siècle, qui pourrait peut-être permettre de mieux cibler ces cellules par de nouveaux médicaments anti-cancéreux que l'on cherche à développer[4]. L'exposition de certaines cellules au bisphénol A pourrait perturber les centrosomes et peut-être expliquer un risque accru de cancer de la prostate chez les hommes exposés à cette molécule (qui est aussi un perturbateur endocrinien)[5].

Le centrosome est une entité très complexe dont le fonctionnement reste quelque peu mystérieux.

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Mitose

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Protofilament

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In Vivo

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In vitro

In vitro (en latin : « sous verre ») s'applique à toute activité expérimentale réalisée sur micro-organismes, organes ou cellules en dehors de leur contexte naturel (en dehors de l'environnement, de l'organisme vivant ou de la cellule) et en conditions définies et contrôlées. Un exemple est la fécondation in vitro (FIV)

Le terme « in vitro » provient du latin qui signifie « sous verre ». Il est à mettre en association avec les termes « in vivo » et « in silico ».

In vivo (en latin : « dans le vivant ») signifie une approche au sein d'un environnement complexe (plus proche des conditions naturelles). Par opposition, les investigations réalisées in vitro sont menées en dehors du milieu naturel, de l'organisme vivant ou de la cellule initiale.

In silico (qui est un néologisme d'inspiration latine), se traduit par des méthodes physiques et/ou mathématiques permettant des modélisations totalement soustraites des conditions naturelles.

In vitro (à la différence de in silico) ne veut pas forcément dire en dehors du vivant puisque des cultures de cellules vivantes peuvent se faire en dehors de leur environnement naturel.

Il existe donc une gradation entre ces trois termes, qui suggère un éloignement plus ou moins marqué des conditions naturelles.

De nombreuses disciplines utilisent des approches in vitro, telles que :

De nombreuses approches expérimentales dans le domaine de la recherche biologique et biotechnologique s’appuient sur des techniques in vitro comme la culture cellulaire[1] ou la culture de végétaux vasculaires[2].

Industrie outils de production médicale et cosmétique

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La production de masse de certains composés et médicaments sont aujourd'hui réalisés grâce aux techniques de production in vitro comme la production d'insuline qui fut la première utilisation de bactéries et levures pour produire une protéine humaine d’intérêt[3],[4] ou de composés cosmétiques[5].

Industrie et outils de production agroalimentaire

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L'utilisation de fermenteur va permettre la synthèse de composés et enzymes pour l’industrie agroalimentaire comme la synthèse de la lactase ou de ferments destinés à la transformation des produits laitiers, la brasserie, la viticulture. De plus, dans le domaine agricole, la multiplication de plantes de consommation et d'ornement est parfois réalisée par micropropagation (culture de végétaux vasculaire) afin de produire rapidement et à grande échelle certaines plantes d’intérêt[6].

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Polymère

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Polarisé

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Protéines :

Il y as des protéines associés aux microtubules (MAP) qui se lient aux microtubules et leur confèrent des fonctions.

Protéines de séquestration :

Dans les microtubules on associe aux monomères d'actine G liée au GTP (vide supra). On associe aux dimères de tubuline libres, des protéines de séquestration appelées stathmines.

Elles ont une double fonction :

principalement elles fixent les dimères de tubuline en forme G libre pour en empêcher la polymérisation ;

mais elles sont impliquées aussi dans la présentation optimale des dimères libres à l’extrémité + des microtubules (stimulation de la polymérisation).

Ces protéines maintiennent une concentration faible des formes G libres (équilibre).

Ces protéines favorisent la dépolymérisation.

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Protéines de fragmentation :

Katanine : notamment pendant le cycle de mitose au moment de la cytodiérèse, il rompt les microtubules en petites fragments qui se dépolymérisent en dimères. Ils peuvent de réassembler.

MCAK : Supprime les dimères des extrémités et entraîne un raccourci du microtubule.

MIDD1 : Elle s'accumule directement proge des microtubules dans les cellules, et in vitro, il s'y lie directement.

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Protéines stabilisatrices :

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Protéines motrice :

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Kinésine :

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GTP :

Le guanosine triphosphate (GTP) est une coenzyme de transfert de groupements phosphate.

Les propriétés du guanosine triphosphate et de ses dérivés, guanosine diphosphate et guanosine monophosphate, sont identiques à celles de l'adénosine triphosphate (et ses dérivés). C'est un donneur de phosphate. Il est hydrolysé par toute une série d'enzymes appelées les GTPases. Ces protéines alternent entre deux conformations : active liée au GTP et inactive liée au GDP. L'équilibre entre ces deux conformations est régulé par des facteurs d'échange (GEF) permettant l'échange du GDP par le GTP, des protéines GAP catalysant l'hydrolyse du GTP, et enfin des protéines GDI inhibant la dissociation du GDP.

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GDP :

La guanosine diphosphate, abrégée en GDP, est un nucléotide. C'est une coenzyme de transfert de groupements phosphate. Elle résulte de l'hydrolyse de la GTP. Le groupement phosphate libéré peut être transféré sur une protéine.

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GTPases :

Les GTPases sont une classe importante d'enzymes qui catalysent l'hydrolyse de la guanosine triphosphate (GTP) pour donner une guanosine diphosphate (GDP) et un ion phosphate. La fixation du GTP est effectuée par un domaine très conservé dans l'évolution, appelé domaine G, caractéristique de l'ensemble de cette superfamille. Cette hydrolyse est en général couplée à un autre processus biologique, comme la transduction du signal dans la cellule. Les GTPases appartiennent à la catégorie EC 3.6.5 de la nomenclature internationale des enzymes.

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Dynéines :

Molécule de kinésine progressant le long d'un microtubule : cette protéine fonctionne comme une nanomachine.

Les moteurs moléculaires sont des ATPases :

Les kinésines, moteurs moléculaires liés à des éléments figurés qui se déplacent vers l'extrémité positive (+) des microtubules; on parle de transport antérograde.

Les dynéines, moteurs moléculaires liés à des éléments figurés qui se déplacent vers l'extrémité négative (-) des microtubules; on parle de transport rétrograde.

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Protéines stabilisatrice :

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MAP2

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Tau

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Tau : elle assure le même rôle que MAP2 mais cette fois ci principalement dans les axones des cellules nerveuses. Lors du dysfonctionnement de cette protéine, on parle de tauopathie, étant l'une des causes (ou conséquences ?) des maladies neurodégénératives comme la maladie d'Alzheimer par exemple.

Dans la maladie d'Alzheimer, la protéine Tau est abondante et anormalement phosphorylée dans les neurones. Ce qui entraine une anomalie dans l'organisation des microtubules qui génère des amas neurofibrillaires avec filaments introduisant une dégénérescence neuronale.

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TUBB, TUBB1, TUBB2A, TUBB2B, TUBB2C, TUBB3, TUBB4, TUBB4Q, TUBB6 et TUBB8.

[centrosomepapers]

Eukaryotic flagella are complex cellular extensions involved in many human diseases gathered under the term ciliopathies. Currently, detailed insights on flagellar structure come mostly from studies on protists. Here, cryo-electron tomography (cryo-ET) was performed on intact human spermatozoon tails and showed a variable number of microtubules in the singlet region (inside the end-piece). Inside the microtubule plus end, a novel left-handed interrupted helix which extends several micrometers was discovered. This structure was named Tail Axoneme Intra-Lumenal Spiral (TAILS) and binds directly to 11 protofilaments on the internal microtubule wall, in a coaxial fashion with the surrounding microtubule lattice. It leaves a gap over the microtubule seam, which was directly visualized in both singlet and doublet microtubules. We speculate that TAILS may stabilize microtubules, enable rapid swimming or play a role in controlling the swimming direction of spermatozoa.

[naivelocus]

Cryo-EM structures of tau filaments from Alzheimer’s disease

Alzheimer’s disease is the most common neurodegenerative disease, and there are no mechanism-based therapies. The disease is defined by the presence of abundant neurofibrillary lesions and neuritic plaques in the cerebral cortex. Neurofibrillary lesions comprise paired helical and straight tau filaments, whereas tau filaments with different morphologies characterize other neurodegenerative diseases. No high-resolution structures of tau filaments are available. Here we present cryo-electron microscopy (cryo-EM) maps at 3.4–3.5 Å resolution and corresponding atomic models of paired helical and straight filaments from the brain of an individual with Alzheimer’s disease. Filament cores are made of two identical protofilaments comprising residues 306–378 of tau protein, which adopt a combined cross-β/β-helix structure and define the seed for tau aggregation. Paired helical and straight filaments differ in their inter-protofilament packing, showing that they are ultrastructural polymorphs. These findings demonstrate that cryo-EM allows atomic characterization of amyloid filaments from patient-derived material, and pave the way for investigation of a range of neurodegenerative diseases.

Nature doi: 10.1038/nature23002

— Nature Latest Research