Name: cell cycle stages in mitosis
Uploaded: 2019-03-11T09:21:14.000Z
Duration: 2 min 3 s
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North Carolina K-12 Science Standard Course of Study

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Mitosis and Cytokinesis

- [Istruttore] Composto
da cinque fasi uniche,

la mitosi è una forma di divisione

in cui il materiale
genetico di una cellula

è suddiviso tra due cellule figlie.

Innanzitutto, durante la
profase negli esseri umani,

la cromatina nucleica si condensa
in cromosomi a forma di X,

composti da coppie di cromatidi sorelle

attaccate alle giunzioni centromere.

Allo stesso tempo, al di fuori del nucleo,

due organelli a forma
di L chiamati centrosomi

migrano verso i lati
opposti delle cellule.

Nel frattempo, le aste dei
microtubuli iniziano a crescere,

sia verso l'interno o
l'esterno della cellula

formando un apparato alberino
a forma di ragnatela.

Successivamente, l'involucro
nucleare si dissolve

durante la prometafase,
esponendo i cromosomi

agli altri contenuti della cella.

Le strutture proteiche compaiono
anche su entrambi i lati

dei centromeri, uno per ogni cromatide.

Una volta che questi
cinetocori si formano,

estendendo i microtubuli interni

li fissano a loro con
ciascun cromatide sorella

legata a un diverso polo cellulare.

La mitosi progredisce poi in metafase

dove l'apparecchiatura
del mandrino si riarrangia

i cromosomi in modo che siano
orientati in modo simile

in una fila fissa lungo
l'equatore della cella.

Con l'anafase, i microtubuli
apposti al cinetocore

si accorciano e i cromatidi
sorella, ora individualmente

denominati cromosomi,
vengono trascinati a parte.

Queste e altre dinamiche dei microtubuli

contribuiscono ad allungare la cellula.

Infine, i cromosomi arrivano
ai lati delle cellule opposte

durante la telofase in cui
l'apparato del fuso si sgancia.

Il materiale genetico si allenta
e due involucri nucleari,

e ne arriva uno attorno
ad ogni set cromosomico.

Durante la telofase, in un
processo distinto chiamata

citochinesi, la cellula è
citoplasmaticamente divisa.

Il risultato finale della
mitosi è una coppia di cellule

geneticamente identico al loro precursore.

Guertin, David A., Susanne Trautmann e Dannel McCollum. "Citocinesi negli eucarioti". Microbiol. Mol. Biol. Rev. 66, n. 2 (1 giugno 2002): 155–78. [<a href="https://doi.org/10.1128/MMBR.66.2.155-178.2002" target="__blank">Fonte</a>]

mitosi e citochinesi

Nelle cellule eucariotiche, il ciclo della cellula, il ciclo di divisione, è diviso in processi cellulari distinti e coordinati che includono la crescita cellulare, la replicazione del DNA/la duplicazione cromosomica, la distribuzione cromosomica 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 per circa 24 ore (nelle cellule umane tipiche) e in due fasi principali distinguibili. La prima fase è la replicazione del DNA, durante la fase S dell'interfase. Il secondo stadio 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 (divario G1 e G2), durante i quali la cella si prepara per la replica e la divisione.

<h4>Il processo di mitosi</h4>

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 fa parte della mitosi.

<h4>Profase</h4>

Quando la cellula entra nella mitosi, i suoi cromosomi replicati iniziano a condensarsi e diventano visibili come strutture threadlike con l'aiuto di proteine note come condensine. L'apparato del mandrino mitotico inizia a formarsi tra i centrosome, che sono stati duplicati durante la fase S, e migra verso poli opposti della cellula. Il mandrino è costituito da strutture filamentose chiamate microtubuli che sono costituite da monomeri proteici di tubulina. I microtubuli di mandrino iniziano ad estendersi verso i cromosomi condensati. Il nucleolo, un componente del nucleo che produce ribosomi, scompare, indicando l'imminente rottura del nucleo.

<h4>Prometafase</h4>

Durante la prometafase, i filamenti di microtubuli dell'apparato del mandrino continuano a crescere e i cromosomi terminano il condensamento. L'involucro nucleare si rompe completamente, rilasciando i cromosomi. Alcuni dei microtubuli si attaccano ai cromosomi rilasciati, legandosi ad una struttura proteica chiamata cinetocoro che è presente sul centromero di ogni coppia di cromatidi sorelle. Microtubuli di spindle da poli opposti si attaccano ai cinetocori e catturano le coppie cromatide sorelle condensate. I microtubuli di spindle che non si attaccano ai cromosomi (microtubuli polari e astrali) aiutano a spingere i mandrini a parte e ancorare i pali del mandrino alla membrana cellulare.

<h4>Metafase</h4>

I microtubuli del mandrino allineano ogni coppia di cromatidi sorelle completamente condensati lungo l'equatore della cellula, alla piastra metafase. La cella è ora pronta per la divisione.

<h4>Anafase</h4>

I microtubuli dei pali opposti del mandrino, che sono attaccati alla struttura del cinetocoro, accorciano e separano i cromatidi della sorella al centromero. Le proteine di coesione che tengono insieme i cromatidi ora si rompono. I microtubuli cinetochore accorcianti fanno sì che ogni cromatide della coppia, ora chiamati cromosomi, migri verso un polo opposto.

<h4>Telofase</h4>

Una volta che i cromosomi raggiungono i poli opposti della cellula, si deformano e si incolano per formare la cromatina. I filamenti di microtubuli del mandrino depolinizzano nei loro monomeri di tubulina, che vengono poi utilizzati come elementi citoscheletrici nelle cellule figlie. Gli inviluppi nucleari si riassemblano attorno a ogni serie di cromosomi.

<h4>Citocinesi</h4>

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 vesciche dell'apparato di Golgi che trasportano glucosio, enzimi e proteine strutturali si uniscono per formare una nuova piastra cellulare nella posizione dell'ex piastra metafase. 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, generando due cellule figlie identiche alla cellula padre. Nella maggior parte delle cellule umane, la mitosi rappresenta circa un'ora del ciclo cellulare di circa 24 ore.

Mitosi e citochinesi

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cell cycle stages in mitosis

Cell cycle stages in mitosis show how a eukaryotic cell copies its DNA and then divides into two daughter cells. The cycle is controlled by regulatory systems and by outside signals that affect cell growth and division. In typical human cells, the full cycle takes about 24 hours and includes two major phases. The first is DNA replication during the S phase of interphase. The second is the mitotic, or M, phase, which includes mitosis and cytokinesis. G1 and G2 are the gap stages between these phases, and they give the cell time to prepare for replication and division.

Mitosis has five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Cytokinesis may begin during anaphase or telophase, depending on the cell, and it is part of the M phase but not part of mitosis. As mitosis begins in prophase, the replicated chromosomes condense and become visible with the help of condensin proteins. The spindle apparatus starts to form between the duplicated centrosomes, which move to opposite poles. This spindle is made of microtubules, which are built from tubulin proteins, and the nucleolus disappears as the nucleus prepares to break down.

During prometaphase, the chromosomes finish condensing and the nuclear envelope breaks down. This releases the chromosomes into the cell. Some spindle microtubules attach to kinetochores, which are protein structures on the centromere of each pair of sister chromatids. Microtubules from opposite poles capture the sister chromatid pairs. Other microtubules, called polar and astral microtubules, help push the spindle poles apart and anchor them to the cell membrane.

In metaphase, the spindle microtubules line up each pair of fully condensed sister chromatids at the equator of the cell. This position is called the metaphase plate. The cell is then ready to divide. In anaphase, the kinetochore microtubules shorten and pull the sister chromatids apart at the centromere. The cohesion proteins that hold the chromatids together break down. Each chromatid is now a chromosome, and it moves toward an opposite pole.

In telophase, the chromosomes reach the poles and begin to decondense into chromatin. The spindle microtubules also depolymerize into tubulin monomers, which can be used again as cytoskeletal elements in the daughter cells. New nuclear envelopes form around each set of chromosomes. Cytokinesis then divides the cytoplasm. In animal cells, actin filaments form a contractile ring in the plasma membrane and create a cleavage furrow that pinches the cell in two. In plant cells, Golgi vesicles carrying glucose, enzymes, and structural proteins join to form a cell plate at the former metaphase plate. The cell plate fuses with the plasma membranes on both sides and develops into a new cell wall. Mitosis is complete, and the result is two daughter cells identical to the parent cell. In most human cells, mitosis takes about one hour of the 24-hour cell cycle.

Cell Cycle Stages in Mitosis

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Learn how the cell cycle leads to mitosis and cytokinesis, from DNA replication and spindle formation to chromosome separation and cell division.

Cell Cycle Stages in Mitosis | JoVE K12

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Cell Cycle Stages in Mitosis

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