Name: anaphase start and chromatid release
Uploaded: 2021-04-07T12:12:01.000Z
Duration: 2 min 17 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-4

Separation of Sister Chromatids

Al final de la metafase, los cromosomas biorientados se alinean en la placa de la metafase. Durante esta fase, los complejos de anillos de proteínas cohesinas mantienen unidas a las cromátidas hermanas en la región del centrómero y evitan que se separen.
La progresión de la metafase a la anafase se desencadena por la fosforilación inducida por la ciclina-Cdk de una enzima ubiquitina ligasa de múltiples subunidades, el complejo promotor de la anafase, también conocido como ciclosoma o APC/C. La APC/C fosforilada se une a una proteína, Cdc20, formando un complejo activo.
El complejo activo APC/C reconoce una proteína inhibidora llamada securina que se une a una enzima proteasa llamada separasa. Antes de este reconocimiento, la securina inhibe la actividad de la separasa.
El complejo activo APC/C marca la securina con la proteína ubiquitina, dirigiéndose a ella para la degradación proteasómica. La destrucción de la securina libera separasa.
El complejo ciclina-Cdk también regula negativamente la actividad de la separasa no unida a través de la fosforilación inhibitoria.
El complejo activo APC/C provoca la ubiquitinación de las ciclinas, dirigiéndose a ellas para la degradación proteasómica. La destrucción de la ciclina elimina la actividad enzimática de las quinasas dependientes de ciclina o Cdks.
La inactivación de Cdks permite que las enzimas fosfatasa desfosforilan la separasa y evita la refosforilación inhibitoria de la separasa mediada por Cdk. La desfosforilación permite que la enzima separasa escinda el complejo de anillos de cohesina que mantiene unidas a las cromátidas hermanas.
La escisión de la cohesina da lugar a la pérdida absoluta de la cohesión de las cromátidas hermanas, lo que marca la transición de la metafase a la anafase. La pérdida de cohesión permite que las cromátidas hermanas se separen y se muevan a polos opuestos del huso.

<ol>
	<li>Claire Acquaviva y Jonathon Pines. 20016. "El complejo promotor de la anafase/ciclosoma: APC/C". Revista de Ciencia Celular. 119: 2401-2404. [<a href="https://jcs.biologists.org/content/119/12/2401#sec-2">Fuente</a>]</li>
	<li>Frank Uhlmann, Friedrich Lottspeich y Kim Nasmyth. 1999. "La separación de cromátidas hermanas al inicio de la anafase es promovida por la escisión de la subunidad de cohesina Scc1." Nature 400 (6739). Grupo Editorial Nature: 37–42. [<a href="https://mcb.berkeley.edu/courses/mcb230/WEB/PAPERS/SCC1.pdf">Fuente</a>]</li>
	<li>Farr, Katie A. y Orna Cohen‐Fix. "La transición de la metafase a la anafase: un caso de destrucción productiva". Revista europea de bioquímica 263, núm. 1 (1999): 14-19.</li>
	<li>Fang, Guowei, Hongtao Yu y W. Kirschner. "Control de las transiciones mitóticas por el complejo promotor de la anafase". Transacciones filosóficas de la Royal Society de Londres. Serie B: Ciencias Biológicas 354, no. 1389 (1999): 1583-1590.</li>
</ol>

separación de cromátidas hermanas

En la transición de la profase a la metafase, hay una reducción de la cohesión a lo largo de los brazos cromosómicos, lo que resulta en la resolución de las cromátidas hermanas. Sin embargo, quedan conexiones de cohesina residuales para mantener unidas a las cromátidas hermanas hasta la transición de la metafase a la anafase. La conexión residual evita cualquier separación prematura de las cromátidas hermanas, bloqueando los riesgos de aneuploidía dentro de las células hijas.

Al inicio de la anafase, se activa la separasa, una enzima proteolítica. La separasa activada escinde la subunidad Scc1 de los anillos de cohesina residuales, lo que resulta en una pérdida total de cohesión. Las cromátidas hermanas se separan en ausencia de fuerza para mantenerlas unidas. La falta de cohesión permite que las fuerzas polares, que se esfuerzan a lo largo de los microtúbulos, tiren de las cromátidas separadas hacia los polos del huso.

En las primeras mitosis, el punto de control del ensamblaje del huso (SAC) prohíbe que el complejo o ciclosoma promotor de la anafase (APC/C) ubiquitine proteínas, como la securina y las ciclinas de fase M, cuya degradación es necesaria para la anafase. Solo cuando cada cromosoma se alinea correctamente en el huso mitótico, el SAC se desactiva para permitir la fosforilación y activación de las subunidades reguladoras de APC/C: CDC20 y CDH1.

El CDC20 es fosforilado por Cdk1/ciclina B para formar APC/C-CDC20 activo. El APC/C-CDC20 activo luego cataliza la degradación de securina, ciclina A y ciclina B para promover la transición a anafase. Debido a que la actividad de Cdk depende de la ciclina, la degradación de la ciclina B da como resultado la pérdida de la actividad de Cdk1. La pérdida del complejo Cdk1/ciclina B inactiva APC/C-CDC20 pero activa otra subunidad reguladora, APC/C-CDH1, que señala la finalización de la transición de metafase a anafase. El activo APC/C-CDH1 facilita la salida mitótica y estabiliza la fase G1 posterior evitando la acumulación prematura de ciclinas mitóticas.

El cambio en las actividades de APC/C-CDC20 y APC/C-CDH1 tiene dos consecuencias importantes. En primer lugar, estas subunidades reguladoras desencadenan especificidades de sustrato superpuestas pero distintas y, por lo tanto, promueven una transición ordenada del ciclo celular. En segundo lugar, CDC20 y CDH1 se regulan mediante diferentes mecanismos. Cuando APC/C-CDC20 está activo, CDH1 sufre una fosforilación inhibidora por la ciclina B/Cdk1, impidiendo que se una a APC/C. Por el contrario, la actividad de CDC20 es inhibida por un complejo de punto de control mitótico, una multiproteína (BUBR1, BUB3, CDC20 y MAD2) activada por el SAC.

Separación de cromátidas hermanas

En la transición de la profase a la metafase, se produce una reducción de la cohesión a lo largo de los brazos cromosómicos, lo que da lugar a la resolución de ...

Education

Educación

JoVE Core

Molecular Biology

Biología Molecular

Unit 2

Unidad 2

Cell Division

División celular

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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 onset of anaphase, separase, a protein-cutting enzyme, becomes active. It cleaves the Scc1 subunit of the remaining cohesin rings. Once that cohesion is lost, the sister chromatids separate without needing a force to pull them apart first. Then the poleward forces along the microtubules can draw the separated chromatids toward the spindle poles.

The spindle assembly checkpoint, or SAC, controls this timing in early mitosis. It blocks the anaphase-promoting complex or cyclosome, called APC/C, from ubiquitinating proteins such as securin and M-phase cyclins until each chromosome is correctly aligned on the mitotic spindle. After alignment, the SAC is turned off. This allows the APC/C regulatory subunits CDC20 and CDH1 to be phosphorylated and activated in sequence.

Phosphorylated CDC20, together with Cdk1/cyclin B, forms active APC/C-CDC20. This complex promotes anaphase by triggering the degradation of securin, cyclin A, and cyclin B. Because Cdk activity depends on cyclins, cyclin B breakdown lowers Cdk1 activity. That loss inactivates APC/C-CDC20 and activates APC/C-CDH1, which signals that the metaphase-to-anaphase transition is complete.

APC/C-CDH1 helps cells exit mitosis and stabilize the next G1 phase by stopping mitotic cyclins from building up too early. The switch between APC/C-CDC20 and APC/C-CDH1 has two important effects. It gives these regulators overlapping but different substrate targets, which helps keep the cell cycle in order. It also reflects different control systems. When APC/C-CDC20 is active, CDH1 is held back by inhibitory phosphorylation from cyclin B/Cdk1. In contrast, CDC20 is blocked by the mitotic checkpoint complex, which includes BUBR1, BUB3, CDC20, and MAD2 and is activated by the SAC.

Anaphase Start and Chromatid Release

mitosis and cytokinesis

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.

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 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 the spindle checkpoint, separase, and APC/C control sister chromatid release at anaphase and help prevent chromosome errors in mitosis.

Anaphase Start and Chromatid Release | JoVE K12

molecular biology

JoVE Core Biología Molecular presenta los procesos moleculares de la célula a través de lecciones claras y concisas de animaciones audiovisuales. Además, en los vídeos de científicos en acción, se muestran aplicaciones de estos conceptos mediante experimentos reales en laboratorios especializados.

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS1-4.

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

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Cell Structure

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Cytoplasm

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The Nucleus

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The Central Dogma

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Nucleic Acids

DNA as a Genetic Template

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Globular and Fibrous Proteins

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Intrinsically Disordered Proteins

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Protein Complex Assembly

Protein and Protein Structures

Conjugated Proteins

Proteins: From Genes to Degradation

Amyloid Fibrils

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Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of amino ...

Ligand Binding Sites

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Proteins are polymers of amino acid residues. They are versatile and responsible for different cellular functions, including DNA replication, molecular ...

Protein-Protein Interfaces

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Cofactors and Coenzymes

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Cooperative Allosteric Transitions

Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

protein-complexes-with-interchangeable-parts

Protein Complexes with Interchangeable Parts

Mechanical Protein Function

Structural Protein Function

Protein Networks

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

HS-LS1-1

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Lipid Digestion

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Overview

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The Parasympathetic Nervous System

Overview

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Physiology of the Circulatory System

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Blood Flow

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Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

HS-LS1-2

Anaphase Start and Chromatid Release

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