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

La mitosi è una forma di divisione cellulare in cui il materiale genetico di una cellula viene suddiviso tra due cellule figlie. 
In primo luogo, durante la profase, la cromatina nucleica si condensa in cromosomi a forma di X composti da coppie di cromatidi fratelli attaccati alle giunzioni del centromero.
Contemporaneamente, i centrosomi migrano verso i lati opposti delle cellule. Mentre lo fanno, i bastoncelli dei microtubuli iniziano a crescere da ciascuno, formando un apparato fuso simile a una ragnatela.
Successivamente, l'involucro nucleare si dissolve durante la prometafase e le strutture proteiche, chiamate cinetocore, appaiono su entrambi i lati dei centromeri, una per ogni cromatina.
Una volta che questi cinetocori si formano, i microtubuli interni che si estendono si fissano ad essi, con ogni cromatide fratello legato a un diverso polo cellulare.
In metafase, l'apparato del fuso riorganizza i cromosomi in modo che siano orientati in una fila fissa lungo l'equatore della cellula.
Con l'anafase, i microtubuli afissi del cinetocore si accorciano e i cromatidi fratelli vengono allontanati. Queste e altre dinamiche dei microtubuli allungano anche la cellula.
Durante la telofase, l'apparato del fuso si scioglie, i cromatidi si allentano e gli inviluppi nucleari si riformano.
Infine, la cellula viene divisa citoplasmaticamente mediante citochinesi, formando una coppia di cellule geneticamente identiche al loro precursore.

<ol>
	<li>Guertin, David A., Susanne Trautmann e Dannel McCollum. "Citocinesi negli eucarioti". Microbiol. Mol. Biol. Rev. 66, n. 2 (1 giugno 2002): 155–78.</li>
</ol>

mitosi e citocinesi

Mitosis And Cytokinesis

Negli eucarioti, il ciclo di divisione cellulare è suddiviso in processi cellulari distinti e coordinati che includono la crescita cellulare, la replicazione del DNA/duplicazione cromosomica, la distribuzione dei cromosomi alle cellule figlie e, infine, la divisione cellulare. Il ciclo cellulare è strettamente regolato dai suoi sistemi regolatori e dai segnali extracellulari che influenzano la proliferazione cellulare.

I processi del ciclo cellulare si verificano nell'arco di circa 24 ore (nelle cellule umane tipiche) e in due fasi principali distinguibili. Il primo stadio è la replicazione del DNA, durante la fase S dell'interfase. La seconda fase è la fase mitotica (M), che prevede la separazione dei cromosomi duplicati in due nuovi nuclei (mitosi) e la divisione citoplasmatica (citocinesi). Le due fasi sono separate da intervalli (gap G1 e G2), durante i quali la cellula si prepara alla replicazione e alla divisione.

Il processo di mitosi

La mitosi può essere divisa in cinque fasi distinte: profase, prometafase, metafase, anafase e telofase. La citocinesi, che inizia durante l'anafase o la telofase (a seconda della cellula), fa parte della fase M ma non della mitosi.

Profase

Quando la cellula entra nella mitosi, i suoi cromosomi replicati iniziano a condensarsi e diventano visibili come strutture filiformi con l'aiuto di proteine note come condensine. L'apparato del fuso mitotico inizia a formarsi tra i centrosomi – che sono stati duplicati durante la fase S – e migra verso i poli opposti della cellula. Il fuso è costituito da strutture filamentose chiamate microtubuli costituiti da monomeri proteici di tubulina. I microtubuli del fuso iniziano ad estendersi verso i cromosomi condensati. Il nucleolo, un componente del nucleo che produce ribosomi, svanisce, indicando l'imminente rottura del nucleo.

Prometafase

Durante la prometafase, i filamenti dei microtubuli dell'apparato del fuso continuano a crescere e i cromosomi finiscono di condensarsi. L'involucro nucleare si rompe completamente, liberando i cromosomi. Alcuni microtubuli si attaccano ai cromosomi rilasciati, legandosi a una struttura proteica chiamata cinetocore che è presente sul centromero di ciascuna coppia di cromatidi fratelli. I microtubuli del fuso provenienti dai poli opposti si attaccano ai cinetocori e catturano le coppie di cromatidi fratelli condensati. I microtubuli del fuso che non si attaccano ai cromosomi (microtubuli polari e astrali) aiutano a separare i fusi e ad ancorare i poli del fuso alla membrana cellulare.

Metafase

I microtubuli del fuso allineano ciascuna coppia di cromatidi fratelli completamente condensati lungo l'equatore della cellula, nella placca metafase. La cellula è ora pronta per dividersi.

Anafase

I microtubuli dei poli opposti del fuso, che sono attaccati alla struttura del cinetocore, accorciano e separano i cromatidi fratelli nel centromero. Le proteine di coesione che tengono insieme i cromatidi ora si rompono. L’accorciamento dei microtubuli del cinetocore fa sì che ciascun cromatide della coppia, ora chiamato cromosomi, migri verso un polo opposto.

Telofase

Una volta che i cromosomi raggiungono i poli opposti della cellula, si decondensano e si srotolano per formare cromatina. I filamenti dei microtubuli del fuso si depolimerizzano nei loro monomeri di tubulina, che vengono poi utilizzati come elementi citoscheletrici nelle cellule figlie. Gli involucri nucleari si ricompongono attorno a ciascun insieme di cromosomi.

Citocinesi

Durante la citocinesi nelle cellule animali, i filamenti di actina formano un anello contrattile nella membrana plasmatica per creare un solco di scissione, che alla fine pizzica la cellula in due. Nelle cellule vegetali, le vescicole dell'apparato di Golgi che trasportano glucosio, enzimi e proteine strutturali si uniscono per formare una nuova placca cellulare nella posizione della precedente placca metafasica. La piastra cellulare in crescita si fonde con le membrane plasmatiche su ciascun lato, formando infine una nuova parete cellulare che divide la cellula in due.

La mitosi è ora completa e genera due cellule figlie identiche alla cellula madre. Nella maggior parte delle cellule umane, la mitosi rappresenta circa un'ora delle circa 24 ore del ciclo cellulare.

Mitosi e citocinesi

Negli eucarioti, il ciclo di divisione cellulare è suddiviso in processi cellulari distinti e coordinati che includono la crescita cellulare, la replicazione del DNA/cromosoma ...

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Essential Cellular Processes

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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

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

Cell Division: Mitosis and Cytokinesis

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