cell division dated 23-08-2013

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binary fission,asexual reproductionby a separation of the body into two new bodies. In the

process of binary fission, an organism duplicates its genetic material, or deoxyribonucleic acid

(DNA), and then divides into two parts (cytokinesis), with each new organism receiving onecopy of DNA.

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Binary fission is the primary method ofreproductionofprokaryoticorganisms. Inprotists,binary fission is often differentiated into types, such as transverse or longitudinal, depending on

the axis ofcellseparation. Regular transverse fission in some organisms, such astapewormsand

scyphostomepolyps, is calledstrobilation. Commonly, this results in a chain, called a strobilus,of the fission productsthe proglottids of tapeworms and the ephyrae of scyphozoanjellyfish;

each proglottid or ephyra matures in turn and separates from the end of the strobilus. A few

metazoan (multicellular) species regularly undergo a body division into several unitssimultaneously, a process calledfragmentation.Planarianfission and fragmentation generallyrepresent direct reproduction in which each portion regenerates missing parts to become a

complete new animal. Strobilation products, however, are only indirectly reproductive:

proglottids are not regenerative but carry and release great numbers of eggs and die; ephyrae donot produce new polyps but mature into sexually reproducingmedusae, the larvae of which

become polyps.
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What Is Binary Fission?

Binary fission is a type of cell division in which a parent cell copies its

genetic material, and then divides, transforming into two daughter cells,

each new cell having one complete copy of the genetic instructionsnecessary to run the cell.
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Advertisement (Bad banner? Pleaselet us know)paramecium (parm`sm), unicellular organism of the genusParamecium, of the ciliate

phylum Ciliophora

found in freshwater throughout the world. Like otherprotozoans

, paramecia, previously considered one-celled animals, are now customarily placed in kingdomProtista

. The paramecium has a stiff outer covering that gives it a permanent slipper shape. It swims

rapidly by coordinated wavelike beats of its many ciliashort, hairlike projections of the cell. A

paramecium normally moves forward in a corkscrew fashion but is capable of reversing directionwhen it encounters adverse conditions. This trial-and-error behavior (backing up and then

continuing forward in a slightly different direction until an optimum path is found) isconspicuous when the animal is observed through a microscope.

Paramecia and other ciliates are the most complex of all single-celled organisms. Theparamecium has an external oral groove lined with cilia and leading to a mouth pore and gullet;

food (typically smaller organisms, such as bacteria) is digested in food vacuoles. There are alsoan anal pore, two contractile vacuoles that regulate the water content of the cell, and two nuclei.

The larger nucleus, or macronucleus, is thought to regulate most cell functions, while the smallernucleus, or micronucleus, is involved in reproduction. Paramecia usually reproduce asexually by

cell division but can also exchange genetic information via a process called conjugation, in

which two individuals unite at the oral grooves and exchange micronuclei that serve as little

packages of DNA, after which the cells divide, yielding daughter cells with DNA from each ofthe parents.
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Amitosis

From Wikipedia, the free encyclopediaJump to:navigation,search

This article needs additional citations for verification. Please helpimprove this article

byadding citations to reliable sources. Unsourced material may bechallengedandremoved.(September 2011)

Amitosis is the process by which acelldirectly separates, not to be confused withmitosis.Amitosis divides relatively simply, as the nucleus andcytoplasmare directly cut in two. Unlike

regular mitosis, nospindlesare involved in amitosis. There is also a lack in the formation and

appearance ofchromosomes. Amitosis is a rare event, but sometimes it is very necessary[1]

and

has been described as a secondary process ofcell divisionin larger life forms, a "forerunner of

degeneration".[2]During binary fission in amoeba, the nucleus divides amitotically into two,which is followed by the division of cytoplasm.
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Cytokinesis

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Jump to:navigation,search

A cell that has almost completed cytokinesis. An arrow points to acentrosomethat can still be

seen.

Cilliate undergoing cytokinesis, with thecleavage furrowbeing clearly visible

Animal celltelophaseand cytokinesis

Cytokinesis, from the greekcyto- (cell) and kinesis (motion, movement), is the process in which

thecytoplasmof a singleeukaryoticcell is divided to form two daughter cells. It usually initiates

during the late stages ofmitosis, and sometimesmeiosis, splitting a mitoticcellin two, to ensurethatchromosomenumber is maintained from one generation to the next. In animal cells, one

notable exception to the normal process of cytokinesis isoogenesis(the creation of anovumin
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theovarian follicleof theovary), where the ovum takes almost all the cytoplasm andorganelles,

leaving very little for the resultingpolar bodies, which then die. In plant cells, a dividing

structure known as the cell plate forms across the centre of the cytoplasm and a new cell wallforms between the two daughter cells.

Cytokinesis is distinguished from theprokaryoticprocess ofbinary fission.
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Study: foetal stem cells repair spinal cord

injury in ratsScience

29 May 13 byLiat Clark
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Shutterstock
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A study has beenpublishedshowing how injecting foetal neural cells into the damaged spinalcords of rats led to a marked regeneration of the neural pathways.

According to a team from the University of California, San Diego School of Medicine andcolleagues in the Czech Republic, the Netherlands and Slovakia, once cells extracted from the

foetal spinal cord were grafted on to the damaged region, links between the injected cells andexisting ones developed and debilitating muscle spasms subsided.

"The primary benefits were improvement in the positioning and control of paws during walking

tests and suppression of muscle spasticity," said Martin Marsala, a professor in UC San Diego'sdepartment of Anesthesiology and coauthor on the paper,publishedin the Stem Cell Research

and Therapy journal online. "We have also demonstrated that grafted neurons can develop
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contacts with the host neurons and, to some extent, restore the connectivity between centres,

above and below the injury, which are involved in motor and sensory processing."

The rats were injured three days prior to treatment, with a circular rod used to compress the L3

vertebra for 15 minutes. Damage to the L3 is associated most commonly with herniated discs and

is a hot spot for chronic back pain in humans. Mice that received the graft also receivedimmunosuppressants for the duration (they died two months later, in a "planned sacrifice") and

the grafts were stained with immunofluorescence so it was clear where the original tissue began

and ended. The subjects were then monitored for any improvements in movement -- notingthings like gait and ability to climb ladders -- and frequency of muscle spasms during computer-

controlled ankle rotations.

Although there wasn't any improvement of note when it came to things like the ladder climbing

test, muscle spasms did significantly subside, normal heat and pain sensitivities returned and the

rats appeared to have better control over their paws. Perhaps more significantly, the team came

away with physical evidence of the regeneration with MRI scans picking up the

immunofluorescent stem cell grafts and showing how they had filled the hole in the spinal regionleft by the rod damage, with the "development of putative GABA-ergic synapses between

grafted and host neurons".

Although the study provided significant results, the team ultimately wants to opt-out of using

embryonic spinal stem cells. This is not because of the inevitable moral questions that arise fromusing foetal cells, but because in an ideal world we don't want to be administering

immunosuppressants -- the only way of avoiding that is to use cells produced by our own bodies.

This could be achieved by using pluripotent stem cells from patients, then turning them into

neural precursors. Making sure these cells are stable enough to insert into a human spinal cord iskey to the therapy being taken forward, but there are already plans to take the study up a notch

with human trials involving patients with injuries between T2 and T12 that have no motor orsensory functions below the injury. It's also already being done elsewhere in the world.

StemCells Inc has been using human neural stem cells derived from adult tissue -- known as

HuCNS-SC cells (an engineered cell devised by the company) -- in small trials on patientssuffering from severe spinal cord injuries. After six months, sensory functions had begun to

return in two of the three patients involved in the trial, with those improvements persisting for

the duration of the year-long trial.

"Between the six- and 12-month evaluations, one patient converted from a complete to an

incomplete injury," said Armin Curt, professor at the Spinal Cord Injury Centre at BalgristUniversity Hospital in Zurich, where the trial took place. "While much more clinical research

needs to be done to demonstrate efficacy, the types of changes we are observing are unexpected

and very encouraging given that these are patients in the chronic stage of complete spinal

injury."

Unlike the rat study, the Zurich trial is not however a controlled clinical study and took in justthose three patients. Nevertheless, the results are astounding and show great promise for using a

patient's own cells one day in the future.


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Elsewhere this week, a team at the University of Wisconsin-Madison School of Veterinary

Medicine has announced it has managed to induceimproved muscle function in ratswith a

model of terminal motor neurone disease ALS, using adult stem cells from human bone marrow.The cells were once again engineered to fulfill a specific function -- in this case the team wanted

them to promote regrowth of damaged nerve cells and targeted the point where the nerve meets

the muscle (where degeneration commonly begins). The cells would not become neurons, butrelease growth factors.

The procedure did not cure the animals of their affliction, but helped slow the disease's progressand reinstate some muscle function. The team's argument is that working with what you've got

left is far easier than starting from scratch and regrowing complex structures using cells that are

potentially unwieldy once injected.

"These motor nerve cells have extremely long connections, and replacing these cells is stillchallenging," said Masatoshi Suzuki, assistant professor of comparative biosciences at UW. "But

we aim to keep the neurons alive and healthy using the same growth factors that the bodycreates, and that's what we have shown here."
http://www.eurekalert.org/pub_releases/2013-05/uow-esc052413.phphttp://www.eurekalert.org/pub_releases/2013-05/uow-esc052413.phphttp://www.eurekalert.org/pub_releases/2013-05/uow-esc052413.phphttp://googleads.g.doubleclick.net/aclk?sa=L&ai=CakqxFDAXUtrwHqfdigfNgIGIB_221a4DAAAQASAAUOzdiLQBYOXq5oO8DoIBF2NhLXB1Yi00MDY4MDY4MDE4Njg3NzA2yAEC4AIAqAMBqgSaAU_QqHsD1U9_fYnxMMvV0MCLCZRZdeuBdRrZx0Y0xow0fn7tpoSN7rJlyWJi_I2Te31MUu3ruh7mUYi3qvKY3BiUdODPmcgNPR-K2StTT3sXA55uvZa3UNEwX7CWbCe77vABEnIJTK1e9MkXA3QPOPgFord47OpNO1KljSv4ZF4fqexfuVLvGvNAVNQJWmADXPndzQQNq3nNpy3gBAGgBhQ&num=0&sig=AOD64_2Cz_Vq_QB48Q_LQ4b5IZXJMgQpzg&client=ca-pub-4068068018687706&adurl=https://www.circules.com/subscribe/wired-uk/131565http://www.eurekalert.org/pub_releases/2013-05/uow-esc052413.php


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Somatic cellFrom Wikipedia, the free encyclopedia


A somatic cell(Greek: /soma = body) is anybiological cellforming the body of anorganism; that is, in amulticellular organism, any cell other than agamete,germ cell,

gametocyteor undifferentiatedstem cell.[1]

By contrast, gametes are cells that fuse duringsexual

reproduction, for organisms that reproduce sexually;Germ cellsare cells that give rise to

gametes;Stem cellsare cells that can divide through mitosis and differentiate into diverse

specialized cell types. For example, inmammals,somatic cells make up all the internal organs,skin, bones, blood and connective tissue. By contrast, mammalian germ cells give rise to

spermatozoaandovawhich fuse duringfertilizationto produce a cell called azygote, whichdevelops into anembryo. Somatic cells arediploid.

[1]

The word "somatic" is derived from theGreekword sma, meaning "body".

Contents

1 Genetics and chromosome content

2 Cloning

3 References 4 See also

Genetics and chromosome content

Like all cells, somatic cells containDNAarranged inchromosomes. If a somatic cell contains

chromosomes arranged in pairs, it is calleddiploidand the organism is called a diploid organism.(The gametes of diploid organisms contain only single unpaired chromosomes and are called

haploid.) Each pair of chromosomes comprises one chromosome inherited from the father and

one inherited from the mother. For example, in humans, somatic cells contain 46chromosomes

organized into 23 pairs. By contrast, gametes of diploid organisms contain only half as many

chromosomes. In humans, this is 23 unpaired chromosomes. When two gametes (i.e. aspermatozoon and an ovum) meet during conception, they fuse together, creating azygote. Due

to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs).

However, a large number ofspecieshave the chromosomes in their somatic cells arranged in

fours ("tetraploid") or even sixes ("hexaploid"). Thus, they can have diploid or even triploidgermline cells. An example of this is the modern cultivated species ofwheat,Triticum aestivum

L., a hexaploid species whose somatic cells contain six copies of everychromatid.
http://en.wikipedia.org/wiki/Somatic_cell#mw-navigationhttp://en.wikipedia.org/wiki/Somatic_cell#mw-navigationhttp://en.wikipedia.org/wiki/Somatic_cell#mw-navigationhttp://en.wikipedia.org/wiki/Somatic_cell#p-searchhttp://en.wikipedia.org/wiki/Somatic_cell#p-searchhttp://en.wikipedia.org/wiki/Somatic_cell#p-searchhttp://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Multicellular_organismhttp://en.wikipedia.org/wiki/Multicellular_organismhttp://en.wikipedia.org/wiki/Multicellular_organismhttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Germ_cellhttp://en.wikipedia.org/wiki/Germ_cellhttp://en.wikipedia.org/wiki/Germ_cellhttp://en.wikipedia.org/wiki/Gametocytehttp://en.wikipedia.org/wiki/Gametocytehttp://en.wikipedia.org/wiki/Stem_cellhttp://en.wikipedia.org/wiki/Stem_cellhttp://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Germ_cellshttp://en.wikipedia.org/wiki/Germ_cellshttp://en.wikipedia.org/wiki/Germ_cellshttp://en.wikipedia.org/wiki/Stem_cellshttp://en.wikipedia.org/wiki/Stem_cellshttp://en.wikipedia.org/wiki/Stem_cellshttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Spermatozoahttp://en.wikipedia.org/wiki/Spermatozoahttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Fertilizationhttp://en.wikipedia.org/wiki/Fertilizationhttp://en.wikipedia.org/wiki/Fertilizationhttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Embryohttp://en.wikipedia.org/wiki/Embryohttp://en.wikipedia.org/wiki/Embryohttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Somatic_cell#Genetics_and_chromosome_contenthttp://en.wikipedia.org/wiki/Somatic_cell#Genetics_and_chromosome_contenthttp://en.wikipedia.org/wiki/Somatic_cell#Cloninghttp://en.wikipedia.org/wiki/Somatic_cell#Cloninghttp://en.wikipedia.org/wiki/Somatic_cell#Referenceshttp://en.wikipedia.org/wiki/Somatic_cell#Referenceshttp://en.wikipedia.org/wiki/Somatic_cell#See_alsohttp://en.wikipedia.org/wiki/Somatic_cell#See_alsohttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Haploidhttp://en.wikipedia.org/wiki/Haploidhttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Tetraploidhttp://en.wikipedia.org/wiki/Tetraploidhttp://en.wikipedia.org/wiki/Hexaploidhttp://en.wikipedia.org/wiki/Hexaploidhttp://en.wikipedia.org/wiki/Hexaploidhttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/Chromatidhttp://en.wikipedia.org/wiki/Chromatidhttp://en.wikipedia.org/wiki/Chromatidhttp://en.wikipedia.org/wiki/Chromatidhttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/Hexaploidhttp://en.wikipedia.org/wiki/Tetraploidhttp://en.wikipedia.org/wiki/Specieshttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Haploidhttp://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Chromosomehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Somatic_cell#See_alsohttp://en.wikipedia.org/wiki/Somatic_cell#Referenceshttp://en.wikipedia.org/wiki/Somatic_cell#Cloninghttp://en.wikipedia.org/wiki/Somatic_cell#Genetics_and_chromosome_contenthttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Diploidhttp://en.wikipedia.org/wiki/Embryohttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Fertilizationhttp://en.wikipedia.org/wiki/Ovumhttp://en.wikipedia.org/wiki/Spermatozoahttp://en.wikipedia.org/wiki/Mammalhttp://en.wikipedia.org/wiki/Stem_cellshttp://en.wikipedia.org/wiki/Germ_cellshttp://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Sexual_reproductionhttp://en.wikipedia.org/wiki/Somatic_cell#cite_note-campbell229-1http://en.wikipedia.org/wiki/Stem_cellhttp://en.wikipedia.org/wiki/Gametocytehttp://en.wikipedia.org/wiki/Germ_cellhttp://en.wikipedia.org/wiki/Gametehttp://en.wikipedia.org/wiki/Multicellular_organismhttp://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Somatic_cell#p-searchhttp://en.wikipedia.org/wiki/Somatic_cell#mw-navigation


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Centrosome



The structure of the centrosome

Cell biology

Theanimal cell
http://en.wikipedia.org/wiki/Centrosome#mw-navigationhttp://en.wikipedia.org/wiki/Centrosome#mw-navigationhttp://en.wikipedia.org/wiki/Centrosome#mw-navigationhttp://en.wikipedia.org/wiki/Centrosome#p-searchhttp://en.wikipedia.org/wiki/Centrosome#p-searchhttp://en.wikipedia.org/wiki/Centrosome#p-searchhttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Animal_cellhttp://en.wikipedia.org/wiki/Animal_cellhttp://en.wikipedia.org/wiki/Animal_cellhttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Centrosome_(borderless_version)-en.svghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Centrosome_(borderless_version)-en.svghttp://en.wikipedia.org/wiki/Animal_cellhttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Centrosome#p-searchhttp://en.wikipedia.org/wiki/Centrosome#mw-navigation


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Components of a typical animal cell:

1. Nucleolus

2. Nucleus

3. Ribosome(little dots)

4. Vesicle5. Rough endoplasmic reticulum

6. Golgi apparatus(or "Golgi body")

7. Cytoskeleton

8. Smooth endoplasmic reticulum

9. Mitochondrion

10.Vacuole

11.Cytosol(fluid that contains organelles)

12.Lysosome

13.Centrosome

14.Cell membrane

Incell biology, the centrosome is anorganellethat serves as the mainmicrotubule organizingcenter(MTOC) of the animalcellas well as a regulator ofcell-cycleprogression. It was

discovered byEdouard Van Benedenin 1883[1]

and was described and named in 1888 by

Theodor Boveri.[2]

The centrosome is thought to have evolved only in themetazoanlineage ofeukaryotic cells.

[3]Fungiandplantsuse other MTOC structures to organize their

microtubules.[4][5]

Although the centrosome has a key role in efficientmitosisin animal cells, it is

not essential.[6][7][8]

Centrosomes are composed of twoorthogonallyarrangedcentriolessurrounded by anamorphous

mass ofproteintermed thepericentriolar material(PCM). The PCM contains proteinsresponsible formicrotubule nucleationand anchoring[9]

including -tubulin,pericentrinand

ninein. In general, each centriole of the centrosome is based on a nine triplet microtubule

assembled in a cartwheel structure, and containscentrin,cenexinandtektin.[10]

Contents

1 Roles of the centrosome

2 Centrosome alterations in cancer cells

o 2.1 Structural aberrations

o 2.2 Numeric aberrations

3 Evolution of the centrosome 4 Centrosome associated nucleotides

5 References
http://en.wikipedia.org/wiki/Nucleolushttp://en.wikipedia.org/wiki/Nucleolushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Vesicle_%28biology_and_chemistry%29http://en.wikipedia.org/wiki/Vesicle_%28biology_and_chemistry%29http://en.wikipedia.org/wiki/Rough_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Rough_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Golgi_apparatushttp://en.wikipedia.org/wiki/Golgi_apparatushttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Smooth_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Smooth_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Vacuolehttp://en.wikipedia.org/wiki/Vacuolehttp://en.wikipedia.org/wiki/Vacuolehttp://en.wikipedia.org/wiki/Cytosolhttp://en.wikipedia.org/wiki/Cytosolhttp://en.wikipedia.org/wiki/Cytosolhttp://en.wikipedia.org/wiki/Lysosomehttp://en.wikipedia.org/wiki/Lysosomehttp://en.wikipedia.org/wiki/Lysosomehttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Cell-cyclehttp://en.wikipedia.org/wiki/Cell-cyclehttp://en.wikipedia.org/wiki/Cell-cyclehttp://en.wikipedia.org/wiki/Edouard_Van_Benedenhttp://en.wikipedia.org/wiki/Edouard_Van_Benedenhttp://en.wikipedia.org/wiki/Edouard_Van_Benedenhttp://en.wikipedia.org/wiki/Centrosome#cite_note-1http://en.wikipedia.org/wiki/Centrosome#cite_note-1http://en.wikipedia.org/wiki/Centrosome#cite_note-1http://en.wikipedia.org/wiki/Theodor_Boverihttp://en.wikipedia.org/wiki/Centrosome#cite_note-2http://en.wikipedia.org/wiki/Centrosome#cite_note-2http://en.wikipedia.org/wiki/Centrosome#cite_note-2http://en.wikipedia.org/wiki/Metazoahttp://en.wikipedia.org/wiki/Metazoahttp://en.wikipedia.org/wiki/Metazoahttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid12224551-4http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid12224551-4http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid12224551-4http://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16546079-6http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16546079-6http://en.wikipedia.org/wiki/Centrosome#cite_note-stowerspr2012-8http://en.wikipedia.org/wiki/Centrosome#cite_note-stowerspr2012-8http://en.wikipedia.org/wiki/Orthogonalhttp://en.wikipedia.org/wiki/Orthogonalhttp://en.wikipedia.org/wiki/Orthogonalhttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Microtubule_nucleationhttp://en.wikipedia.org/wiki/Microtubule_nucleationhttp://en.wikipedia.org/wiki/Microtubule_nucleationhttp://en.wikipedia.org/wiki/Centrosome#cite_note-9http://en.wikipedia.org/wiki/Centrosome#cite_note-9http://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Pericentrinhttp://en.wikipedia.org/wiki/Pericentrinhttp://en.wikipedia.org/wiki/Pericentrinhttp://en.wikipedia.org/wiki/Nineinhttp://en.wikipedia.org/wiki/Nineinhttp://en.wikipedia.org/wiki/Centrinhttp://en.wikipedia.org/wiki/Centrinhttp://en.wikipedia.org/wiki/Centrinhttp://en.wikipedia.org/wiki/Cenexinhttp://en.wikipedia.org/wiki/Cenexinhttp://en.wikipedia.org/wiki/Cenexinhttp://en.wikipedia.org/wiki/Tektinhttp://en.wikipedia.org/wiki/Tektinhttp://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#Roles_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#Roles_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#Centrosome_alterations_in_cancer_cellshttp://en.wikipedia.org/wiki/Centrosome#Centrosome_alterations_in_cancer_cellshttp://en.wikipedia.org/wiki/Centrosome#Structural_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Structural_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Numeric_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Numeric_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Evolution_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#Evolution_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#Centrosome_associated_nucleotideshttp://en.wikipedia.org/wiki/Centrosome#Centrosome_associated_nucleotideshttp://en.wikipedia.org/wiki/Centrosome#Referenceshttp://en.wikipedia.org/wiki/Centrosome#Referenceshttp://en.wikipedia.org/wiki/Centrosome#Referenceshttp://en.wikipedia.org/wiki/Centrosome#Centrosome_associated_nucleotideshttp://en.wikipedia.org/wiki/Centrosome#Evolution_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#Numeric_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Structural_aberrationshttp://en.wikipedia.org/wiki/Centrosome#Centrosome_alterations_in_cancer_cellshttp://en.wikipedia.org/wiki/Centrosome#Roles_of_the_centrosomehttp://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Tektinhttp://en.wikipedia.org/wiki/Cenexinhttp://en.wikipedia.org/wiki/Centrinhttp://en.wikipedia.org/wiki/Nineinhttp://en.wikipedia.org/wiki/Pericentrinhttp://en.wikipedia.org/wiki/Tubulinhttp://en.wikipedia.org/wiki/Centrosome#cite_note-9http://en.wikipedia.org/wiki/Microtubule_nucleationhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Proteinhttp://en.wikipedia.org/wiki/Amorphoushttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Orthogonalhttp://en.wikipedia.org/wiki/Centrosome#cite_note-stowerspr2012-8http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16546079-6http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16546079-6http://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid12224551-4http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid12224551-4http://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Fungushttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Metazoahttp://en.wikipedia.org/wiki/Centrosome#cite_note-2http://en.wikipedia.org/wiki/Theodor_Boverihttp://en.wikipedia.org/wiki/Centrosome#cite_note-1http://en.wikipedia.org/wiki/Edouard_Van_Benedenhttp://en.wikipedia.org/wiki/Cell-cyclehttp://en.wikipedia.org/wiki/Cell_%28biology%29http://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Organellehttp://en.wikipedia.org/wiki/Cell_biologyhttp://en.wikipedia.org/wiki/Cell_membranehttp://en.wikipedia.org/wiki/Lysosomehttp://en.wikipedia.org/wiki/Cytosolhttp://en.wikipedia.org/wiki/Vacuolehttp://en.wikipedia.org/wiki/Mitochondrionhttp://en.wikipedia.org/wiki/Smooth_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Golgi_apparatushttp://en.wikipedia.org/wiki/Rough_endoplasmic_reticulumhttp://en.wikipedia.org/wiki/Vesicle_%28biology_and_chemistry%29http://en.wikipedia.org/wiki/Ribosomehttp://en.wikipedia.org/wiki/Cell_nucleushttp://en.wikipedia.org/wiki/Nucleolus


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Roles of the centrosome

Role of the centrosome in cell cycle progression

Centrosomes are associated with thenuclear membraneduringprophaseof the cell cycle. Inmitosisthe nuclear membrane breaks down and the centrosome nucleatedmicrotubules(parts ofthecytoskeleton) can interact with thechromosomesto build themitotic spindle.

The mother centriole, the older of the two in the centriole pair, also has a central role in making

ciliaandflagella.[10]

The centrosome is copied only once percell cycleso that each daughter cell inherits one

centrosome, containing two structures called centrioles (see also:centrosome cycle). The

centrosome replicates during theS phaseof the cell cycle. During theprophasein the process of

cell division calledmitosis, the centrosomes migrate to opposite poles of the cell. The mitoticspindle then forms between the two centrosomes. Upon division, each daughter cell receives one

centrosome. Aberrant numbers of centrosomes in a cell have been associated withcancer.

Doubling of a centrosome is similar toDNA replicationin two respects: thesemiconservativenature of the process and the action ofcdk2as a regulator of the process.

[11]But the processes are

essentially different in that centrosome doubling does not occur by template reading and

assembly. The mother centriole just aids in the accumulation of materials required for the

assembly of the daughter centriole.[12]
http://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/Nuclear_membranehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Ciliahttp://en.wikipedia.org/wiki/Ciliahttp://en.wikipedia.org/wiki/Flagellahttp://en.wikipedia.org/wiki/Flagellahttp://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Centrosome_cyclehttp://en.wikipedia.org/wiki/Centrosome_cyclehttp://en.wikipedia.org/wiki/Centrosome_cyclehttp://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/Semiconservative_replicationhttp://en.wikipedia.org/wiki/Semiconservative_replicationhttp://en.wikipedia.org/wiki/Semiconservative_replicationhttp://en.wikipedia.org/wiki/Cdk2http://en.wikipedia.org/wiki/Cdk2http://en.wikipedia.org/wiki/Cdk2http://en.wikipedia.org/wiki/Centrosome#cite_note-11http://en.wikipedia.org/wiki/Centrosome#cite_note-11http://en.wikipedia.org/wiki/Centrosome#cite_note-11http://en.wikipedia.org/wiki/Centrosome#cite_note-12http://en.wikipedia.org/wiki/Centrosome#cite_note-12http://en.wikipedia.org/wiki/Centrosome#cite_note-12http://en.wikipedia.org/wiki/File:Molly_Sheehan_Wikipedia_1.jpghttp://en.wikipedia.org/wiki/File:Molly_Sheehan_Wikipedia_1.jpghttp://en.wikipedia.org/wiki/File:Molly_Sheehan_Wikipedia_1.jpghttp://en.wikipedia.org/wiki/File:Molly_Sheehan_Wikipedia_1.jpghttp://en.wikipedia.org/wiki/Centrosome#cite_note-12http://en.wikipedia.org/wiki/Centrosome#cite_note-11http://en.wikipedia.org/wiki/Cdk2http://en.wikipedia.org/wiki/Semiconservative_replicationhttp://en.wikipedia.org/wiki/DNA_replicationhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/S_phasehttp://en.wikipedia.org/wiki/Centrosome_cyclehttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Flagellahttp://en.wikipedia.org/wiki/Ciliahttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Chromosomeshttp://en.wikipedia.org/wiki/Cytoskeletonhttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Prophasehttp://en.wikipedia.org/wiki/Nuclear_membrane


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Centrosome (shown by arrow) next to nucleus

Interestingly, centrioles are not required for the progression of mitosis. When the centrioles areirradiated by a laser, mitosis proceeds normally with a morphologically normal spindle.

Moreover, development of the fruit flyDrosophilais largely normal when centrioles are absentdue to a mutation in a gene required for their duplication.

[13]In the absence of the centrioles the

microtubules of the spindle are focused by motors allowing the formation of a bipolar spindle.

Many cells can completely undergo interphase without centrioles.[10]

Unlike centrioles,centrosomes are required for survival of the organism. Acentrosomal cells lack radial arrays of

astral microtubules. They are also defective in spindle positioning and in ability to establish a

central localization site in cytokinesis. The function of centrosome in this context is hypothesized

to ensure the fidelity ofcell divisionbecause it greatly increases the efficacy. Some cell typesarrest in the following cell cycle when centrosomes are absent. This is not a universal

phenomenon.

When the nematodeC. elegansegg is fertilized the sperm delivers a pair of centrioles. These

centrioles will form the centrosomes which will direct the first cell division of thezygoteand thiswill determine its polarity. It is not yet clear whether the role of the centrosome in polarity

determination is microtubule dependent or independent.

Centrosome alterations in cancer cells

Theodor Boveri, in 1914, described centrosome aberrations incancercells. This initialobservation was subsequently extended to many types of human tumors.

[14]Centrosome

alterations in cancer can be divided in two subgroups, structural or numeric aberrations, yet bothcan be simultaneously found in a tumor.
http://en.wikipedia.org/wiki/Drosophilahttp://en.wikipedia.org/wiki/Drosophilahttp://en.wikipedia.org/wiki/Drosophilahttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16814722-13http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16814722-13http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16814722-13http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Astral_microtubuleshttp://en.wikipedia.org/wiki/Astral_microtubuleshttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Caenorhabditis_eleganshttp://en.wikipedia.org/wiki/Caenorhabditis_eleganshttp://en.wikipedia.org/wiki/Caenorhabditis_eleganshttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Theodor_Boverihttp://en.wikipedia.org/wiki/Theodor_Boverihttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/File:Cytokinesis-electron-micrograph.jpghttp://en.wikipedia.org/wiki/File:Cytokinesis-electron-micrograph.jpghttp://en.wikipedia.org/wiki/File:Cytokinesis-electron-micrograph.jpghttp://en.wikipedia.org/wiki/File:Cytokinesis-electron-micrograph.jpghttp://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Cancerhttp://en.wikipedia.org/wiki/Theodor_Boverihttp://en.wikipedia.org/wiki/Zygotehttp://en.wikipedia.org/wiki/Caenorhabditis_eleganshttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Astral_microtubuleshttp://en.wikipedia.org/wiki/Centrosome#cite_note-rieder-10http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid16814722-13http://en.wikipedia.org/wiki/Drosophila


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Structural aberrations

Usually they appear due to uncontrolled expression of centrosome components, or due to post-translational modifications (such as phosphorylations) which are not adequate for those

components. These modifications may produce variations in centrosome size (usually too big,

due to an excess of pericentriolar material). On top of this, due to the fact that centrosomalproteins have the tendency to form aggregates, often centrosome-related bodies (CRBs) are

observed in ectopic places.[15]

Both enlarged centrosomes and CRBs are similar to the

centrosomal structures observed in tumors,.[16]

Even more, these structures can be induced inculture cells by overexpression of specific centrosomal proteins, such as CNap-1 or Nlp.

[15][17]

These structures may look very similar, yet detailed studies reveal that they may present very

different properties, depending on their proteic composition. For instance, their capacity to

incorporate -TuRC complexes (see also:-tubulin) can be very variable, and so their capacity tonucleatemicrotubules,

[16]therefore affecting in different way the shape, polarity and motility of

implicated tumor cells.

Numeric aberrations

The presence of an inadequate number of centrosomes is very often linked to the apparition ofgenome instabilityand the loss of tissular differentiation.

[16][18]However, the method to count the

centrosome number (each one with 2 centrioles) is often not very precise, because it is frequently

assesed using fluorescence microscopy, whose resolution capacity is not the best. Nevertheless,it is clear that the presence of supernumerary (in excess) centrosomes is a common event in

human tumors. It has been observed that loss of the tumor-suppressor proteinp53produces

supernumerary centrosomes,[19]

as well as deregulation of other proteins implicated in

tumorigenesisin humans, such asBRCA1andBRCA2(for references, see[14]

). It is important tonote that supernumerary centrosomes can be generated by very different mechanisms: specific

reduplication of the centrosome, failure duringcell division(generating an increase inchromosome number), cell fusion (for instance due to infection by specific viruses) orde novogeneration of centrosomes. At this point there is not sufficient information to know how frequent

are those mechanisms in vivo, but it is possible that the increase in centrosome numbers due a

failure during cell division might be more frequent than appreciated, because many "primary"defects in one cell (deregulation of thecell cycle, defectiveDNAorchromatinmetabolism,

failure in thespindle checkpoint, etc...) would generate a failure in cell division, an increase in

ploidyand an increase in centrosome numbers as a "secondary" effect.[20][21]

Evolution of the centrosome

Theevolutionaryhistory of the centrosome and thecentriolehas been traced for some of thesignature genes, e.g. thecentrins.

[3]Centrins participate incalcium signalingand are required for

centriole duplication.[22]

There exist two main subfamilies of centrins, both of which are present

in the early-branchingeukaryoteGiardia intestinalis. Centrins have therefore been present in the

common ancestor of eukaryotes. Conversely, they have no recognizablehomologsinarcheaandbacteriaand are thus part of the "eukaryotic signature genes." Although there are studies on the

evolution of the centrins and centrioles,[3][23]

no studies have been published on the evolution of

thepericentriolar material.
http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Tubulin#.CE.B3-Tubulinhttp://en.wikipedia.org/wiki/Tubulin#.CE.B3-Tubulinhttp://en.wikipedia.org/wiki/Tubulin#.CE.B3-Tubulinhttp://en.wikipedia.org/wiki/Tubulin#.CE.B3-Tubulinhttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Genome_instabilityhttp://en.wikipedia.org/wiki/Genome_instabilityhttp://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/P53http://en.wikipedia.org/wiki/P53http://en.wikipedia.org/wiki/P53http://en.wikipedia.org/wiki/Centrosome#cite_note-19http://en.wikipedia.org/wiki/Centrosome#cite_note-19http://en.wikipedia.org/wiki/Centrosome#cite_note-19http://en.wikipedia.org/wiki/Tumorigenesishttp://en.wikipedia.org/wiki/Tumorigenesishttp://en.wikipedia.org/wiki/BRCA1http://en.wikipedia.org/wiki/BRCA1http://en.wikipedia.org/wiki/BRCA1http://en.wikipedia.org/wiki/BRCA2http://en.wikipedia.org/wiki/BRCA2http://en.wikipedia.org/wiki/BRCA2http://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/Spindle_checkpointhttp://en.wikipedia.org/wiki/Spindle_checkpointhttp://en.wikipedia.org/wiki/Spindle_checkpointhttp://en.wikipedia.org/wiki/Ploidyhttp://en.wikipedia.org/wiki/Ploidyhttp://en.wikipedia.org/wiki/Centrosome#cite_note-20http://en.wikipedia.org/wiki/Centrosome#cite_note-20http://en.wikipedia.org/wiki/Centrosome#cite_note-20http://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Centrinshttp://en.wikipedia.org/wiki/Centrinshttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Calcium_signalinghttp://en.wikipedia.org/wiki/Calcium_signalinghttp://en.wikipedia.org/wiki/Calcium_signalinghttp://en.wikipedia.org/wiki/Centrosome#cite_note-22http://en.wikipedia.org/wiki/Centrosome#cite_note-22http://en.wikipedia.org/wiki/Centrosome#cite_note-22http://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Giardia_intestinalishttp://en.wikipedia.org/wiki/Giardia_intestinalishttp://en.wikipedia.org/wiki/Giardia_intestinalishttp://en.wikipedia.org/wiki/Homology_%28biology%29http://en.wikipedia.org/wiki/Homology_%28biology%29http://en.wikipedia.org/wiki/Homology_%28biology%29http://en.wikipedia.org/wiki/Archeahttp://en.wikipedia.org/wiki/Archeahttp://en.wikipedia.org/wiki/Archeahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Pericentriolar_materialhttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Bacteriahttp://en.wikipedia.org/wiki/Archeahttp://en.wikipedia.org/wiki/Homology_%28biology%29http://en.wikipedia.org/wiki/Giardia_intestinalishttp://en.wikipedia.org/wiki/Eukaryotehttp://en.wikipedia.org/wiki/Centrosome#cite_note-22http://en.wikipedia.org/wiki/Calcium_signalinghttp://en.wikipedia.org/wiki/Centrosome#cite_note-pmid17977464-3http://en.wikipedia.org/wiki/Centrinshttp://en.wikipedia.org/wiki/Centriolehttp://en.wikipedia.org/wiki/Evolutionhttp://en.wikipedia.org/wiki/Centrosome#cite_note-20http://en.wikipedia.org/wiki/Centrosome#cite_note-20http://en.wikipedia.org/wiki/Ploidyhttp://en.wikipedia.org/wiki/Spindle_checkpointhttp://en.wikipedia.org/wiki/Chromatinhttp://en.wikipedia.org/wiki/DNAhttp://en.wikipedia.org/wiki/Cell_cyclehttp://en.wikipedia.org/wiki/Cell_divisionhttp://en.wikipedia.org/wiki/Centrosome#cite_note-Nigg2002-14http://en.wikipedia.org/wiki/BRCA2http://en.wikipedia.org/wiki/BRCA1http://en.wikipedia.org/wiki/Tumorigenesishttp://en.wikipedia.org/wiki/Centrosome#cite_note-19http://en.wikipedia.org/wiki/P53http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Genome_instabilityhttp://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Tubulin#.CE.B3-Tubulinhttp://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15http://en.wikipedia.org/wiki/Centrosome#cite_note-Lingle2002-16http://en.wikipedia.org/wiki/Centrosome#cite_note-Casenghi2003-15


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It is evident that some parts of the centrosome are highly diverged in the model species

Drosophila melanogasterandCaenorhabditis elegans. For example, both species have lost one

of the centrin subfamilies that are usually associated with centriole duplication.Drosophila

melanogastermutants that lack centrosomes can even develop to morphologically normal adult

flies, which then die shortly after birth because their sensory neurons lackcilia.[13]

Thus, these

flies have evolved functionally redundant machinery, which is independent of the centrosomes.

Centrosome associated nucleotides

Research in 2006[24]

indicated that centrosomes fromSurf clameggs containRNAsequences.The sequences identified were found in "few to no" other places in the cell, and do not appear in

existinggenomedatabases. One identified RNA sequence contains a putativeRNA polymerase,

leading to the hypothesis of an RNA based genome within the centrosome. However, subsequent

research has shown that centrosome do not contain their own DNA-based genomes. While it wasconfirmed that RNA molecules associate with centrosomes, the sequences have still been found

within the nucleus. Furthermore, centrosomes can form de novo after having been removed (e.g.

by laser irradiation) from normal cells.[23]
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Chromatid



Chromosomalcomponents:

(1) Chromatid

(2)Centromere

(3) Short arm(4) Long arm

A chromatid is one copy of a duplicatedchromosome, which generally is joined to the othercopy by acentromere,

[1]for the process ofnuclear division(mitosisormeiosis). They are

normally identical ("homozygous") but may have slight differences in the case of mutations, in

which case they areheterozygous. They are calledsister chromatidsso long as they are joined bythe centromeres. When they separate (duringanaphaseof mitosis and anaphase 2 of meiosis), the

strands are called daughter chromosomes (although having the same genetic mass as the

individual chromatids that made up its parent, the daughter "molecules" are still referred to aschromosomes much as one child is not referred to as a single twin). Before replication, one

chromosome is composed of one DNA molecule and after there are two DNA molecules. This is

because DNA replication increases the amount of DNA and does not increase the number of

chromosomes.

In other words, a chromatid is "one-half of two [normally] identical copies of a replicated

chromosome".[2]

The two copies may have slight differences due to mutations. A chromatid issimply a copied chromosome which is paired with a (normally) identical chromosome at the

centromere. It should not be confused with theploidyof an organism, which is the number ofhomologous versionsof a chromosome.
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What is the difference between monad dyad

and tetrad?

In:The Difference Between[Edit categories]

ChromosomesDiscuss everthing to do withChromosomeswww.everything.org.uk/Chromosomes

AdsAnswer:

Chromosomes come in 2 forms, depending on the stage of the cell cycle.

The monad form consists of a single chromatid, a single piece of DNA containing a centromere

and telomeres at the ends.The dyad form consists of 2 identical chromatids (sister chromatids) attached together at the

centromere.Chromosomes are in the dyad form before mitosis, and in the monad form after mitosis.

The dyad form is the result of DNA replication: a single piece of DNA (the monad chromosome)

replicated to form 2 identical DNA molecules (the 2 chromatids of the dyad chromosome).

a tetrad is a pair of homologous chromosomes that have replicated and come together inprophase I of meiosis; and consists of four chromatids.
http://www.answers.com/T/The_Difference_Betweenhttp://www.answers.com/T/The_Difference_Betweenhttp://www.answers.com/T/The_Difference_Betweenhttp://void%280%29/http://void%280%29/http://void%280%29/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://www.google.com/aclk?sa=L&ai=CEnX_nzEXUpHoAer3iQLPxIHYA_C1sosEwJ2RsknV_pYGCAAQASD0yfYCUJ77h_b______wFg5ermg7wOyAEBqQKz4idatqFQPqoEI0_QkqtP0udT_spAxt0eTsWwSjSZMI12XqBvFZ2px6qFVrxngAfo6LIm&sig=AOD64_0Q-dv5pITD7lcKoz58V0Y1BrEIGg&adurl=http://www.everything.org.uk/http://void%280%29/http://www.answers.com/T/The_Difference_Between


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Astral microtubules



This diagram depicts the organization of a typicalmitotic spindlefound inanimalcells.

Chromosomes are attached to kinetochore microtubules via a multiprotein complex called thekinetochore. Polar microtubules interdigitate at the spindle midzone and push the spindle poles

apart via motor proteins. Astral microtubules anchor the spindle poles to the cell membrane.

Microtubule polymerization is nucleated at themicrotubule organizing center.

Astral microtubules are a subpopulation ofmicrotubules, which only exist during andimmediately beforemitosis. They are defined as any microtubule originating from thecentrosomewhich does not connect to akinetochore.

[1]Astral microtubules develop in the actin

skeleton and interact with the cell cortex to aid in spindle orientation. They are organized into

radial arrays around the centrosomes. The turn-over rate of this population of microtubules ishigher than any other population.

The role of astral microtubules is assisted bydyneinsspecific to this role. These dyneins havetheir light chains (static portion) attached to the cell membrane, and their globular parts (dynamic

portions) attached to the microtubules. The globular chains attempt to move towards the

centrosome, but as they are bound to the cell membrane, this results in pulling the centrosomes

towards the membrane, thus assistingcytokinesis.

Astral microtubules are not required for the progression of mitosis, but they are required to

ensure the fidelity of the process. The functions of astral microtubules can be generallyconsidered as determination of cell geometry. It is absolutely required for correct positioning and

orientation ofmitotic spindleapparatus. It is also involved in determination of cell division site

based on the geometry and polarity of the cells.
http://en.wikipedia.org/wiki/Astral_microtubules#mw-navigationhttp://en.wikipedia.org/wiki/Astral_microtubules#mw-navigationhttp://en.wikipedia.org/wiki/Astral_microtubules#mw-navigationhttp://en.wikipedia.org/wiki/Astral_microtubules#p-searchhttp://en.wikipedia.org/wiki/Astral_microtubules#p-searchhttp://en.wikipedia.org/wiki/Astral_microtubules#p-searchhttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Centrosomehttp://en.wikipedia.org/wiki/Centrosomehttp://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Astral_microtubules#cite_note-1http://en.wikipedia.org/wiki/Astral_microtubules#cite_note-1http://en.wikipedia.org/wiki/Astral_microtubules#cite_note-1http://en.wikipedia.org/wiki/Dyneinhttp://en.wikipedia.org/wiki/Dyneinhttp://en.wikipedia.org/wiki/Dyneinhttp://en.wikipedia.org/wiki/Cytokinesishttp://en.wikipedia.org/wiki/Cytokinesishttp://en.wikipedia.org/wiki/Cytokinesishttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/File:Spindle_apparatus.svghttp://en.wikipedia.org/wiki/File:Spindle_apparatus.svghttp://en.wikipedia.org/wiki/File:Spindle_apparatus.svghttp://en.wikipedia.org/wiki/File:Spindle_apparatus.svghttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Cytokinesishttp://en.wikipedia.org/wiki/Dyneinhttp://en.wikipedia.org/wiki/Astral_microtubules#cite_note-1http://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Centrosomehttp://en.wikipedia.org/wiki/Mitosishttp://en.wikipedia.org/wiki/Microtubulehttp://en.wikipedia.org/wiki/Microtubule_organizing_centerhttp://en.wikipedia.org/wiki/Kinetochorehttp://en.wikipedia.org/wiki/Animalhttp://en.wikipedia.org/wiki/Mitotic_spindlehttp://en.wikipedia.org/wiki/Astral_microtubules#p-searchhttp://en.wikipedia.org/wiki/Astral_microtubules#mw-navigation


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The maintenance of astral microtubules is dependent on the integrity of centrosome. It is also

dependent on several microtubule-associated proteins such asEB1andAdenomatous Polyposis

Coli(APC).

Microsoft Office Word 2007.lnk Astral rays:
http://en.wikipedia.org/wiki/MAPRE1http://en.wikipedia.org/wiki/MAPRE1http://en.wikipedia.org/wiki/MAPRE1http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/APC_%28protein%29http://en.wikipedia.org/wiki/MAPRE1


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Periphery

outskirts - circumference - perimeter circuit

, the line around the circle, circumference, part of a circle, an arc, the outer surface)


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Interpolar fibres:

+

+

+

+

+

+ +

sisterchromatidskinetochore centrosome

interpolarmicrotubulesastralmicrotubules

kinetochoremicrotubules

cellmembrane

sisterchromatidskinetochore cell wallkinetochore

microtubulescellmembrane

2 m2 m

cell division dated 23-08-2013

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