Name: chromatid movement by microtubule forces
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 1 min 39 s
Channel: JoVE
Description: 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.

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

Anaphase A and B

הפרדת הכרומוזומים מתרחשת במהלך אנאפאזה: כאשר הכרומטידים האחיות נפרדים והכרומטידים הבודדים נעים לעבר הקטבים המנוגדים של התא.
התקדמות אנאפאזה מהווה שני תהליכים עצמאיים אך חופפים: אנאפאזה א' ואנאפאזה ב'.
במהלך אנאפאזה A, בהיעדר לכידות אחות-כרומטית, שני כוחות קוטביים פועלים על הכרומוזומים.
מיקרוטובול פלוס סוף דה-פולימריזציה בקינטוחור מייצר כוח קוטבי. שטף מיקרוטובול, מדה-פולימריזציה של קצה מינוס, יוצר גם כוח קוטבי. השילוב של שני כוחות קוטביים אלה, המלווה בקיצור של המיקרוטובולים הקינטוכוריים, מושך את הכרומטידים הבודדים לעבר מוטות הצירים.
כאשר כרומוזומי הבת נעים לעבר הקטבים, מתחיל שלב B, ומוטות הציר מופרדים, ומאריכים את הציר. החלבונים המוטוריים, קינזין-5 ודינין, מניעים את הפרדת מוטות הצירים.
חלבונים מוטוריים קינזין-5 מצליבים את קצוות הפלוס של מיקרוטובולים בין-קוטביים חופפים. חלבונים מוטוריים אלה בעלי כיוון פלוס קצה יוצרים כוח לאחור לאורך המיקרוטובולים הדוחפים את מוטות הציר זה מזה. 
חלבונים מוטוריים של דינאין מקשרים בין מיקרוטובולים אסטרליים עם מרכיבי קליפת התא. חלבונים מוטוריים מכווני מינוס אלה יוצרים כוח, ומושכים את מוטות הציר לכיוון קליפת התא.

<ol>
	<li>אלברטס, ברוס. "מנועים מולקולריים". ביולוגיה מולקולרית של התא. מהדורה רביעית. הספרייה הלאומית לרפואה של ארצות הברית, 1 בינואר 1970. [<a href="https://www.ncbi.nlm.nih.gov/books/NBK26888/">מקור</a>]</li>
	<li>Joglekar, Ajit P, Kerry S Bloom ואד סלמון. 2010. "מנגנונים של יצירת כוח על ידי קצה על Kinetochore-Microtubule מצורף." דעה נוכחית בביולוגיה של התא 22 (1). Elsevier בע"מ: 57–67. [<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822009/">מקור</a>]</li>
	<li>חודג'קוב, אלכסיי וטרון קאפור. 2005. "שטף מיקרוטובול: בשביל מה זה טוב?" ביולוגיה נוכחית 15 (23). Elsevier Inc: R966–R968. [<a href="https://www.sciencedirect.com/science/article/pii/S0960982205013928">מקור</a>]</li>
</ol>

אנפאזה a ו-b

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מיקרו-צינוריות נוצרות באמצעות פולימירזציה מקצה לקצה של הטרודימרים טובולין. מקורם של מיקרו-צינוריות קינטוכור מקטבי הציר, וקצוות הפלוס שלהם מתחברים עם הקינטוכורים על כרומטידות אחיות. קומפלקסים של חלבון Ndc80, הקיימים על הקינטוכור, יוצרים קישורים בעלי זיקה נמוכה עם הקצה הפלוס של מיקרו-צינוריות הקינטוכורים הללו.

דה-פולימריזציה פלוס-אנד משחררת הטרודימרים של טובולין מהאזור הטרמינלי של המיקרו-צינור. כאשר תת-יחידות טובולין אובדות, הקומפלקסים של Ndc80 מתנתקים ומתחברים מחדש באתרים לפני מקטע הדפולימריזציה של המיקרו-צינור. התהליך מביא להזזה לכיוון הקוטב, מושך את הקינטוכור והכרומטיד הקשור אליו לכיוון קוטב הציר.

שטף המיקרו-צינורי מושך את הכרומטידות לכיוון מוטות הציר.

תת-יחידות הטובולין היוצרות את סריג המיקרוטובוליות נעות ברציפות לעבר קצה המינוס, ומציגות שטף מיקרוטובולי מכוון מינוס.

שטף מיקרו-צינוריות מתפתח כאשר דה-פולימריזציה מתמשכת בקצה המינוס מאוזנת על ידי פילמור מתמשך בקצה הפלוס. קצב קבוע של דה-פולימריזציה ופילמור שומר על אורך מיקרו-צינוריות קבוע בעוד שיחידות המשנה הבודדות בתוך הסריג נעות לעבר קצה הדה-פולימריזציה .

מיקרוטובולים של קינטוכור העוברים שטף מושכים את הקינטוכורים והכרומטידות הקשורות אליהם לאורך כיוון השטף, לכיוון קטבי הציר.

חלבונים מוטוריים מיקרוטובוליים - דיניין וקינזין-5

דיניינים הם חלבונים מוטוריים מכוונים למיקרו-צינוריות מינוס-קצה. דיניינים מקשרים את הקצוות הפלוסים של מיקרו-צינוריות האסטרליים עם רכיבי שלד התא בקליפת התא, ובכך ממקמים את קטבי הציר בתוך התא. התנועה המכוונת לקצה המינוס של דיניינים יוצרת כוח המושך את מוטות הציר לכיוון קליפת התא.

קינזין-5 הם חלבונים מוטוריים מכוונים פלוס-קצה. קינזין-5 מקיים אינטראקציה עם הקצוות הפלוסים של מיקרוטובולים אינטרפולריים אנטי-מקבילים באזור האמצע של הציר. מנועי המיקרו-צינוריות הללו עוזרים למיקרו-צינוריות הבין-קוטביות להחליק אחת על פני השניה תוך יצירת כוח הדוחף את מוטות הציר זה מזה.
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אנפאזה A ו-B

מיקרוטובולים נוצרים באמצעות פילמור מקצה לקצה של הטרודימרים טובולין. מיקרוטובולים Kinetochore מקורם מוטות ציר, ואת ...

Education

JoVE Core

Molecular Biology

ביולוגיה מולקולרית

Unit 2

יחידה 2

Cell Division

חלוקת תאים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

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.

Chromatid Movement by Microtubule Forces

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 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 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

See how kinetochore microtubules, Ndc80, microtubule flux, dynein, and kinesin-5 help move chromatids and position the spindle during anaphase.

Chromatid Movement by Microtubule Forces | JoVE K12

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HS-LS1-4.

Characteristics of Life

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Globular and Fibrous Proteins

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Intrinsically Disordered Proteins

Ribosomes

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Protein Complex Assembly

Protein and Protein Structures

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Protein Complexes with Interchangeable Parts

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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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Animal and Plant Cell Structure

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Lipid Digestion

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Overview

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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

Chromatid Movement by Microtubule Forces

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