Name: mitosis and cytokinesis stages
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 3 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Heredity

Cellular genetics

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

In eukaryotes, the cell division cycle is divided into distinct, coordinated cellular processes that include cell growth, DNA replication/chromosome ...

Education

Didattica

JoVE Core

Molecular Biology

Biologia Molecolare

Unit 2

Unità 2

Cell Division

Divisione cellulare

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

mitosis and cytokinesis stages

Mitosis and cytokinesis are the two main steps of cell division. Mitosis is the process that divides the nucleus, while cytokinesis splits the rest of the cell.

During mitosis, the cell’s genetic material is separated into two sets. This helps form two new nuclei with the same genetic information. Cytokinesis then completes division by separating the cytoplasm, which creates two daughter cells.

These stages work together to make cell division possible in growing and repairing tissues. Understanding mitosis and cytokinesis helps explain how one cell becomes two.

Mitosis and Cytokinesis Stages

mitosis and cytokinesis

Mitosis and cytokinesis are the two main steps of cell division. Mitosis is the process that divides the nucleus, while cytokinesis splits the rest of the cell. During mitosis, the cell’s genetic material is separated into two sets. This helps form two new nuclei with the same genetic information. Cytokinesis then completes division by separating the cytoplasm, which creates two daughter cells. These stages work together to make cell division possible in growing and repairing tissues.

duplication of chromatin structure

Chromatin Rebuilding During DNA Replication

Chromatin rebuilding during DNA replication helps cells copy DNA and pass on chromosome structure to daughter cells. During cell division, the genome must be disrupted and then reassembled across the whole chromosome. This process allows chromatin to be inherited, rebuilt, and maintained in new cells. The basic unit of chromatin is the nucleosome. A nucleosome contains DNA wrapped around an octamer of histone proteins, with short linker DNA between neighboring nucleosomes. The histone proteins...

cohesins

Cohesins in Meiosis and Genetic Disorders

Cohesin protein complexes act like molecular glue that keeps sister chromatids together. They are important in both mitosis and meiosis. In mitosis, cohesin complexes are removed from chromosomes before anaphase begins. Meiosis has two rounds of chromosome separation. Meiosis I separates homologous chromosomes, while Meiosis II separates sister chromatids. This process produces four daughter cells. The Meiosis I cohesin complex is made of four subunits: Smc1, Smc3, Rec8, and Scc3. Rec8...

condensins

How Condensins Shape Mitotic Chromosomes

Condensins shape chromosomes during mitosis, the stage when a cell divides. These large protein complexes use ATP, the cell’s energy molecule, to help turn loose post-interphase DNA into compact, separate chromosomes. They organize and segregate chromosomal DNA so it can be passed on correctly. Plant and animal cells contain two condensin complexes: condensin I and condensin II. Each complex has five subunits. Two are SMC, or Structural Maintenance of Chromosomes, subunits. One is a kleisin...

the mitotic spindle

How the Mitotic Spindle Separates Chromosomes

The mitotic spindle is a microtubule-based structure that helps separate chromosomes during cell division. It forms in eukaryotic cells and moves sister chromatids to opposite ends of the parent cell. This leaves each new cell nucleus with the correct genetic material. A bipolar spindle has two poles, and that shape is important for chromosome segregation. In many animal cells, two centrosomes are present when mitosis begins. Each centrosome helps organize a circular set of microtubules at one...

centrosome duplication

Centrosome Duplication in the Cell Cycle

Centrosome duplication is a key part of the animal cell cycle. The centrosome is the main microtubule organizing center, or MTOC, in animal cells. It contains two cylindrical centrioles at its core. Each centriole has nine sets of three microtubules held together by proteins. The two centrioles sit at right angles and are surrounded by the pericentriolar matrix, or PCM, a shapeless protein cloud. Duplication starts early in the cell cycle so each daughter cell can receive a centrosome after...

microtubule instability

Microtubule Growth and Shrinkage

Microtubules are hollow, cylindrical filaments in the cell. They are about 25 nm wide and can range from 200 nm to 25 μm in length. Their main building blocks are GTP-bound tubulin subunits that form αβ-heterodimers, which then assemble into protofilaments. These protofilaments join by lateral bonds to create stable microtubule cylinders. Microtubules are highly dynamic because they repeatedly assemble and break down. They can even grow on one end while shrinking on the other at the same time.

spindle assembly

How the Mitotic Spindle Forms

The mitotic spindle forms through centrosome-mediated, chromatin-mediated, and microtubule-mediated pathways. These pathways often work at the same time. Together, they build a strong spindle apparatus for cell division. In most cells, centrosomes are the main sites where microtubules begin to grow. During the G2 to prophase transition, centrosomes mature and make more microtubules. The growing microtubules extend from both centrosomes, and their plus-ends search for chromosomes by attaching...

attachment of sister chromatids

Kinetochore-Microtubule Binding in Mitosis

Kinetochore-microtubule binding helps chromosomes line up and separate during mitosis. After the nuclear envelope breaks down, condensed chromosomes are exposed to the bipolar microtubules of the mitotic spindle. The kinetochore is a large, disc-shaped protein complex at the centromere region of each sister chromatid, and it serves as the microtubule binding site. Usually, the plus-end of a single microtubule inserts into the kinetochore. In some cases, a kinetochore first makes lateral...

forces acting on chromosomes

Chromosome Movement During Mitosis

Chromosome movement during mitosis depends on several small forces that act at different times and positions in the cell. In prometaphase, these forces help chromosomes move to the equatorial plane and line up at the metaphase plate. Because the forces change with location and stage, chromosome behavior also changes as mitosis continues. Microtubules and motor proteins create two main kinds of force on chromosomes: poleward force and anti-poleward force, also called polar-ejection force.

separation of sister chromatids

Anaphase Start and Chromatid Release

Anaphase starts when sister chromatids are released from one another and pulled toward opposite spindle poles. Before that happens, cohesion along the chromosomal arms is reduced from prophase to metaphase, which helps the sister chromatids resolve. A residual cohesin link still holds them together until the metaphase-to-anaphase transition. This leftover connection helps prevent early separation and reduces the risk of aneuploidy, or the wrong number of chromosomes, in daughter cells. At the...

the spindle assembly checkpoint

How Cells Safeguard Chromosome Separation

The spindle assembly checkpoint helps cells safeguard chromosome separation during anaphase. It acts as a molecular surveillance system. The checkpoint checks whether the steps needed for chromosome segregation are complete before the cell moves on. Many proteins work together to control this checkpoint. If mutations affect these proteins, a cell may enter anaphase too early. Chromosomes can then separate before the needed steps are finished. When this happens, the daughter cells may receive...

anaphase a and b

Chromatid Movement by Microtubule Forces

Chromatid movement during anaphase depends on microtubule forces at the spindle. Kinetochore microtubules grow from the spindle poles, and their plus ends attach to kinetochores on sister chromatids. The kinetochore protein complex Ndc80 makes low-affinity links with the microtubule plus end.

the contractile ring

How Cells Build the Contractile Ring

Contractile rings are built from microfilaments and help separate daughter cells during cytokinesis. This ring forms as the cell cycle moves forward, but the exact timing and coordination with other cell cycle events are still not fully understood. RhoA, a small GTPase in the Ras superfamily, controls contractile ring assembly and function. The inactive form of RhoA is bound to GDP. A guanine nucleotide exchange factor, or Rho-GEF, is located in the cortex region, where the next cell division...

determining the plane of cell division

How Cells Set the Division Plane

How cells set the division plane during cell division affects daughter cell size and, in many cases, cell fate. The plane of division is perpendicular to the plane of chromosome segregation. Different organisms use different cues to place it, based on their shape and needs. In animal cells, the cleavage furrow forms along the division plane from the cell cortex, the area just below the plasma membrane. The mitotic spindle is the main guide for this position. If the spindle axis changes, the...

the phragmoplast

How Plant Cells Build a New Wall

Plant cells build a new wall during cytokinesis with help from the phragmoplast. This plant structure forms from the central spindle and related cell parts as the cell finishes dividing. In animal cells, the comparable structure is the midbody, but in plants the phragmoplast expands outward to guide new wall formation. The mature phragmoplast has a donut-like shape. It has an outer leading region, a middle transition zone, and an inner lagging region. New microtubules are assembled...

distribution of cytoplasmic content

How Organelles Are Split During Cytokinesis

Cytokinesis splits a cell’s chromosomes and organelles into two daughter cells. Before cell division, organelles grow and divide. They cannot be made from scratch, so each daughter cell must inherit at least one copy to survive. Many details of this organelle sorting process are still not fully known. The cytoplasm contains organelles, salts, proteins, and water. Small organelles such as peroxisomes and lysosomes can be shared by simple diffusion. Because cells contain many copies of these...

anaphase promoting complex

APC Activates Chromosome Separation

The anaphase-promoting complex, or APC, helps control cell cycle progression by destroying specific proteins at the right time. These proteins are tagged with ubiquitin by ubiquitin ligases and then broken down by the proteasome. The SCF (Skp1/Cullin/F-box) complex and APC are two major ubiquitin ligases involved in this process. SCF stays active throughout the cell cycle, but APC turns on during the metaphase-to-anaphase transition. APC becomes active when Cdc20 or Cdh1 binds to it. These...

key terms and concepts

Learn how mitosis separates the nucleus and cytokinesis divides the cytoplasm to form two daughter cells. Clear high school cell division content.

Mitosis and Cytokinesis Stages | JoVE K12

molecular biology

Le video animazioni di JoVE Core Molecular Biology, organizzate in video lezioni, illustrano i processi molecolari cellulari in maniera chiara e concisa. Inoltre, nei video di "scienziati in azione", i concetti scientifici vengono applicati e dimostrati da ricercatori attraverso esperimenti in laboratorio.

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Mitosis and Cytokinesis Stages

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