The spindle is... Description, structure and functions

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2018-03-26 03:46:10

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The Spindle is a temporary structure formed during the processes of mitosis and meiosis, and provides segregation of chromosomes and cell division. It is bipolar: a system of microtubules formed in the space between the poles is shaped like a spindle. In the area of centromere for chromosomes kinetochores join the microtubules of the spindle. According to him, the chromosomes move to the poles.


the spindle is

Structure

The Spindle consists of three major structural elements: microtubules, poles and fission of chromosomes. Poles of dividing animals is organized using a centrosome containing a centriole. In the case of the absence of the centrosome (plants and oocytes in several species) the spindle has broad poles called centrosomal. In the formation of spindles involved another structure of the motor proteins. They belong to Geneina and kinesins.

The Spindle is a bipolar structure. Both poles are located in the centrosome - organelles, which are the centers of organization of microtubules. In the structure of the centrosome there are two centriole surrounded by many different proteins. Condensed chromosomes with two chromatids, bound at the site of the centromere, are located between the poles. In the area of the centromere are kinetochore, which is the attachment of microtubules.

Formation

Since the spindle is the structure responsible for cell division, the beginning of its Assembly occurs in prophase. In plants and in oocytes in the absence of the centrosome, the centre of the organization of microtubules serves as the core framework. Microtubules close to the nuclear envelope and at the end of prophase the end of their orientation, and formed a "prophase spindle" - the axis of the future spindle.

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Due to the fact that in animal cells the centrosome is exactly what performs the role of the center of the organization, the beginning of the formation of the spindle is the discrepancy of the two centrosome during the period of prophase. This is possible thanks to Geneina motor proteins: they are attached to the outer surface of the core and on the inner side of the cell membrane. Group Dineyev attached to the membrane, is connected with the astral microtubules and they move towards the minus-end, due to what is happening and dilution of the centrosome at the opposite sites of the cell membrane.

in the formation of spindle involved

After the build

The Final spindle formation occurs at the stage of prometaphase, after the disappearance of the membrane of the nucleus it becomes full, because then the centrosome and microtubules can gain access to the components of the spindle.
However there is one exception: the budding yeast spindle formation occurs inside the nucleus.

The Formation of threads of the spindle and their orientation is impossible without two processes: the organization of microtubules around the chromosomes and attach them to each other on opposite poles of the division. Many of the elements needed for the final formation of the division apparatus, including chromosomes, and motor proteins are inside the nucleus and microtubules, and, if animal cells, the centrosome is contained in the cytoplasm, that is the components isolated from each other. That is why education of the spindle ends only after the disappearance of the nuclear envelope.

spindle formation occurs

Accession chromosome

In the formation of spindle protein involved, as well as many other structures, and in animal cells this process is well studied. During the period of prophase microtubules form around the centrosome stellate structure, which diverges in the radial direction. After the membrane of the nucleus breaks down, dynamically unstable microtubules are beginning to probe this area and kinetochore chromosomes can gain a foothold on them. Some part of the chromosome is immediately transferred to the opposite poles, and the remaining first contact with the microtubules of one of the poles, and then start moving towards the desired pole. When the process is completed, chromosomes are already associated with any pole, you begin to kinetochore attached to microtubules from opposite poles, thus, during the metaphase to kinetochores is attached from ten to forty tubes. This education is called kinetochores beam. Gradually each of the chromosomes appear to be associated with the opposite pole, and they form a Central part of the spindle metaphase plate.

 spindle comprises

Second option

There is another scenario, which may form the spindle. It is possible for cells with centrosome and to the cells where they are absent. The process involved in gamma-tubulinovykh ring complex, due to which there is a short nucleation of microtubules around chromosomes. Tubules join kinetochore plus-end, followed by polymerization of the microtubules, i.e., adjustable height. Minus-ends "merge" and remain at the poles due to the division of motor proteins. If in the formation of spindle centrosome pair is involved, this facilitates the connection of microtubules, but the process is possible withoutthem.

the formation of the spindle fibres of the dividing

Equally

A Clear division of chromosomes between two cells formed during division, can only occur if the paired chromatids their kinetochore joined different poles. Bipolar divergence of chromatids is called amfitaminka, but there are other options that occur during how going to the spindle. It monotipical (one kinetochore is attached to one pole) and sinteticheskie (both kinetochore chromosome is connected with one pole). When marataizes one kinetochore captured from the two poles. Stable is only conventional, bipolar bond, which occurs due to forces of tension from the poles, other methods of bonding fragile and reversible, but possible because of the location kinetochore.


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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."

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