Name: cell division: mitosis and cytokinesis
Uploaded: 2023-06-23T15:38:45.000Z
Duration: 1 min 35 s
Channel: JoVE

La mitose est une forme de division cellulaire où le matériel génétique d'une cellule est réparti entre deux cellules filles. 
Tout d’abord, au cours de la prophase, la chromatine nucléique se condense en chromosomes en forme de X composés de paires de chromatides sœurs attachées aux jonctions centromères.
En même temps, les centrosomes migrent vers les côtés cellulaires opposés. Ce faisant, des tiges de microtubules commencent à se développer à partir de chacun, formant un appareil de fuseau en forme de toile.
Ensuite, l’enveloppe nucléaire se dissout au cours de la prométaphase et les structures protéiques, appelées kinétochores, apparaissent des deux côtés des centromères, une pour chaque chromatine.
Une fois que ces kinétochores se forment, des microtubules internes en expansion s’y fixent, chaque chromatide sœur étant attachée à un pôle cellulaire différent.
En métaphase, l'appareil fusiforme réorganise les chromosomes de sorte qu'ils soient orientés en une rangée fixe le long de l'équateur de la cellule.
Avec l’anaphase, les microtubules fixés aux kinétochores se raccourcissent et les chromatides sœurs sont écartées. Celles-ci et d’autres dynamiques des microtubules allongent également la cellule.
Au cours de la télophase, l’appareil de fuseau se dissout, les chromatides se desserrent et les enveloppes nucléaires se reforment.
Enfin, la cellule est divisée cytoplasmiquement par cytokinèse, formant une paire de cellules génétiquement identiques à leur précurseur.

<ol>
	<li>Guertin, David A., Susanne Trautmann et Dannel McCollum. « Cytokinèse chez les eucaryotes. » Microbiol. Mol. Biol. Rev. 66, n° 2 (1er juin 2002) : 155-78.</li>
</ol>

mitose et cytokinèse

Mitosis And Cytokinesis

Chez les eucaryotes, le cycle de division cellulaire est divisé en processus cellulaires distincts et coordonnés qui comprennent la croissance cellulaire, la réplication de l'ADN/duplication des chromosomes, la distribution des chromosomes aux cellules filles et enfin la division cellulaire. Le cycle cellulaire est étroitement régulé par ses systèmes de régulation ainsi que par les signaux extracellulaires qui affectent la prolifération cellulaire.

Les processus du cycle cellulaire se déroulent sur environ 24 heures (dans les cellules humaines typiques) et en deux étapes principales distinctes. La première étape est la réplication de l’ADN, pendant la phase S de l’interphase. La deuxième étape est la phase mitotique (M), qui implique la séparation des chromosomes dupliqués en deux nouveaux noyaux (mitose) et la division cytoplasmique (cytodiérèse). Les deux phases sont séparées par des intervalles (intervalles G_1 et G_2), pendant lesquels la cellule se prépare à la réplication et à la division.

Le processus de mitose

La mitose peut être divisée en cinq étapes distinctes : prophase, prométaphase, métaphase, anaphase et télophase. La cytodiérèse, qui commence pendant l'anaphase ou la télophase (selon la cellule), fait partie de la phase M mais ne fait pas partie de la mitose.

Prophase

Lorsque la cellule entre en mitose, ses chromosomes répliqués commencent à se condenser et à devenir visibles sous forme de structures filiformes à l'aide de protéines appelées condensines. L'appareil du fuseau mitotique commence à se former entre les centrosomes, qui ont été dupliqués pendant la phase S, et migre vers les pôles opposés de la cellule. Le fuseau est constitué de structures filamenteuses appelées microtubules constituées de monomères protéiques de tubuline. Les microtubules du fuseau commencent à s'étendre vers les chromosomes condensés. Le nucléole, un composant du noyau qui produit les ribosomes, disparaît, indiquant la rupture imminente du noyau.

Prométaphase

Pendant la prométaphase, les filaments microtubulaires de l'appareil fusiforme continuent de croître et les chromosomes finissent de se condenser. L'enveloppe nucléaire se décompose complètement, libérant les chromosomes. Certains microtubules s'attachent aux chromosomes libérés et se lient à une structure protéique appelée kinétochore, présente sur le centromère de chaque paire de chromatides sœurs. Les microtubules du fuseau des pôles opposés s'attachent aux kinétochores et capturent les paires condensées de chromatides sœurs. Les microtubules du fuseau qui ne s'attachent pas aux chromosomes (microtubules polaires et astraux) aident à écarter les fuseaux et à ancrer les pôles du fuseau à la membrane cellulaire.

Métaphase

Les microtubules du fuseau alignent chaque paire de chromatides sœurs entièrement condensées le long de l'équateur de la cellule, au niveau de la plaque métaphase. La cellule est maintenant prête à se diviser.

Anaphase

Les microtubules des pôles opposés du fuseau, qui sont attachés à la structure du kinétochore, raccourcissent et séparent les chromatides sœurs au niveau du centromère. Les protéines de cohésion qui maintiennent les chromatides ensemble se décomposent désormais. Le raccourcissement des microtubules du kinétochore fait migrer chaque chromatide de la paire, maintenant appelée chromosomes, vers un pôle opposé.

Télophase

Une fois que les chromosomes atteignent les pôles opposés de la cellule, ils se décondensent et se déroulent pour former la chromatine. Les filaments des microtubules du fuseau se dépolymérisent en leurs monomères de tubuline, qui sont ensuite utilisés comme éléments du cytosquelette dans les cellules filles. Les enveloppes nucléaires se réassemblent autour de chaque ensemble de chromosomes.

Cytodiérèse

Au cours de la Cytodiérèse dans les cellules animales, les filaments d'actine forment un anneau contractile dans la membrane plasmique pour créer un sillon de clivage qui finit par pincer la cellule en deux. Dans les cellules végétales, les vésicules de l'appareil de Golgi transportant du glucose, des enzymes et des protéines structurelles se rejoignent pour former une nouvelle plaque cellulaire à l'emplacement de l'ancienne plaque métaphasique. La plaque cellulaire en croissance fusionne avec les membranes plasmiques de chaque côté, formant finalement une nouvelle paroi cellulaire qui divise la cellule en deux.

La mitose est désormais terminée, générant deux cellules filles identiques à la cellule mère. Dans la plupart des cellules humaines, la mitose représente environ une heure sur un cycle cellulaire d'environ 24 heures.

Mitose et cytokinèse

Chez les eucaryotes, le cycle de division cellulaire est divisé en processus cellulaires distincts et coordonnés qui incluent la croissance cellulaire, la réplication de l’ADN/chromosomes ...

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cell division: mitosis and cytokinesis

Cell division depends on mitosis and cytokinesis. Mitosis is the stage when the cell’s nucleus divides and the copied chromosomes are separated into two sets. Cytokinesis is the step that follows and splits the cell into two daughter cells.

These two processes work together to make sure each new cell receives genetic material and its own cytoplasm. Mitosis keeps the chromosome sets organized, while cytokinesis finishes the division of the whole cell. Together, they create two separate cells from one starting cell.

Cell Division: Mitosis and Cytokinesis

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mitosis and cytokinesis

Cell division depends on mitosis and cytokinesis. Mitosis is the stage when the cell’s nucleus divides and the copied chromosomes are separated into two sets. Cytokinesis is the step that follows and splits the cell into two daughter cells. These two processes work together to make sure each new cell receives genetic material and its own cytoplasm. Mitosis keeps the chromosome sets organized, while cytokinesis finishes the division of the whole cell. Together, they create two separate cells...

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key terms and concepts

Learn how mitosis separates copied chromosomes and how cytokinesis divides the cell into two daughter cells in this high school biology page.

Cell Division: Mitosis and Cytokinesis | JoVE K12

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Cell Division: Mitosis and Cytokinesis

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