Cell division spindle achromatic, or mitotic, spindle, a formation that arises in an animal and plant cell during its mitotic division (Mitosis e) and takes part in the divergence of chromosomes (See Chromosomes) .
V. d. k. - part of the mitotic apparatus; consists of 2 types of cytoplasmic threads: central, connecting both poles of the cell, and chromosomal, going from the poles to the chromosomes (the part of the chromosome to which the spindle thread is attached is called the centromere, or kinetochore). The spindle threads are tubular formations, about 200 A in diameter. V. d. k. has birefringence. The divergence of chromosomes is associated, on the one hand, with the shortening of chromosomal threads, on the other, with the lengthening of the central threads of V. d.c. The mechanism of this phenomenon has not yet been clarified, M. E. Aspiz.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
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CELL DIVISION SPINDLE- a figure (formation) in the form of a thick spindle that appears during cell division and disappears at the end of division. The V. d. c. consists of protoplasmic filaments, one end is attached to the chromosomes, the other end converges to the poles... ... Dictionary of botanical terms
SPINDLE, a rod-shaped system of microtubules in the cytoplasm of a cell during MITOSIS or MEIOSIS. CHROMOSOMES are attached to the bulge of the spindle (equator). The spindle causes chromosomes to separate, causing cells to divide. cm … Scientific and technical encyclopedic dictionary
spindle- ANIMAL EMBRYOLOGY SPINDLE, MITOTIC SPINDLE - a system of microtubules in a dividing cell, which ensures changes in cell parameters and chromosome divergence in mitosis and meiosis. Spindle formation ends in metaphase... General embryology: Terminological dictionary
This article lacks links to sources of information. Information must be verifiable, otherwise it may be questioned and deleted. You can... Wikipedia
- (fusus divisionis) cellular structure that ensures uniform chromosome separation during mitosis or meiosis; V. d. arises in prophase and consists of central threads connecting both poles of the cell, and chromosomal threads connecting the poles with ... Large medical dictionary
Structure consisting of microtubules and associated proteins; is formed during mitosis (In prophase) between two pairs of csntrioles (ed.). Microtubules extend from the poles of the cell and meet at the equator, giving this... ... Medical terms
SPINDLE- (spindle) structure consisting of microtubules and proteins associated with them; is formed during mitosis (In prophase) between two pairs of csntrioles (ed.). Microtubules extend from the poles of the cell and meet at the equator... ... Explanatory dictionary of medicine
achromatic spindle- a structure that arises from microtubules in prophase of mitosis and is a system of thin threads running from the poles of the cell to its center. In anaphase of mitosis A. v. d. pulls single-chromatid chromosomes to different poles of the cell... Anatomy and morphology of plants
Spindle in divisions- Spindle, c. divisions * veraciano, c. spindle * spindle an achromatic cell component consisting of filaments or microtubules, functioning as an organizer of certain forces under the influence of which the movement of chromosomes occurs (metaphase and ... ... Genetics. encyclopedic Dictionary
Cell division is the process of formation of two or more daughter cells from a parent cell. Contents 1 Division of prokaryotic cells 2 Division of eukaryotic cells ... Wikipedia
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What does "spindle" mean?
Dictionary of medical terms
spindle of division (fusus divisionis)
cellular structure that ensures uniform segregation of chromosomes during mitosis or meiosis; V. d. arises in prophase and consists of central threads connecting both poles of the cell and chromosomal threads connecting the poles with chromosomes.
Encyclopedic Dictionary, 1998
spindle
in biology, a system of microtubules in a dividing cell that ensures divergence and strictly identical (during mitosis) distribution of chromosomes between daughter cells.
Wikipedia
Spindle
Spindle- a dynamic structure that is formed in mitosis and meiosis to ensure chromosome segregation and cell division. A typical spindle is bipolar - a spindle-shaped system of microtubules is formed between the two poles. Spindle microtubules attach to chromatid kinetochores in the centromere region and ensure the movement of chromosomes towards the poles.
The spindle is formed by three main structural elements: microtubules, division poles and chromosomes. Centrosomes containing centrioles participate in the organization of division poles in animals. In plants, as well as in the oocytes of some animals, centrosomes are absent, and an acentrosomal spindle with wide poles is formed. Motor proteins belonging to the dynein and kinesin families play an important role in spindle formation.
A complete spindle is formed at the prometaphase stage after the destruction of the nuclear membrane, when cytoplasmic microtubules and centrosomes gain access to chromosomes and other spindle components. An exception is the spindle of budding yeast, which forms inside the nucleus.
metaphase cell antitumor microtubule
Microtubules
During mitosis, a molecular machine called the mitotic spindle operates in the cell (Fig. 1). Its task is to distribute chromosomes to daughter cells. The spindle consists of two centrosomes, called cell centers, and microtubules.
Figure 1 - Scheme of the spindle: 1 - chromosomes; 2 -- spindle poles, centrosomes; 3 -- interpolar microtubules; 4 -- kinetochore microtubules; 5 -- astral microtubules
Microtubules are pole, kinetochore and astral. Polar ones are responsible for the separation of centrosomes, kinetochores attach to chromosomes and move them, and astral ones attach to the inner surface of the cell and fix the division poles. Microtubules are responsible for the movement of chromosomes. Let's look at their structure in more detail.
Each microtubule is a hollow cylinder with an outer diameter of 25 nm, an inner diameter of 15 nm, and a length of up to several micrometers. Their main component is tubulin. In the cell, it is in the form of a dimer consisting of two forms - α- and β-tubulin. Standing on top of each other, tubulin molecules form a protofilament, and 13 protofilaments, connecting with their sides, form a microtubule (this does not mean that when a microtubule is formed, protofilaments are first formed, which are then linked by their sides) (Fig. 2, A).
Figure 2 - Structure and dynamics of microtubules: A. Tubulin dimer is a component of the protofilament in a microtubule. B. Electron microphotographs and conventional images of the ends of a growing and depolymerizing microtubule
A microtubule can polymerize, i.e., grow; when individual dimers attach to it, they attach reversibly. Under normal conditions, this process occurs continuously if there is a lot of tubulin in the solution; as a result, the tube gradually grows, despite the disconnection.
The average rate of microtubule growth depends on the concentration of tubulin in solution. Due to the polarity of the tubulin molecule, the microtubule itself is polar: the end ending with?-tubulin polymerizes faster and is called the plus end, respectively, the second end ends with?-tubulin and is called the minus end; The minus end is attached to the cell center, and the plus end is attached to the chromosome.
Only tubulin bound to a guanosine triphosphate (GTP) molecule can polymerize. However, while in the microtubule, GTP gradually hydrolyzes to guanosine diphosphate (GDP). Therefore, while almost the entire microtubule consists of GDP-tubulin, there is a “cap” of GTP-tubulin at the plus end. Since energy is released during hydrolysis and the natural state of GDP-tubulin is a curved protofilament, the absence of such a “cap” would lead the microtubule to catastrophic depolymerization (“cracking” of the microtubule) (Fig. 2, B). Experiments show that microtubule stability requires at least two layers of GTP tubulin.
It has been known for quite some time that, under laboratory conditions, microtubule depolymerization can produce work (Coue et al., 1991). However, at that time it was still impossible to completely exclude the influence of ATP-dependent motors on chromosome movement.
To test whether tubulin depolymerization alone could produce enough mechanical work to move chromosomes, in a well-studied yeast cell that had a known genome and three motor proteins that could move chromosomes, all the genes responsible for these proteins were removed. All such cells turned out to be viable and capable of dividing, which, however, proceeded more slowly and with a large number of errors. Thus, it was shown that motor proteins are not necessary for division and the main work of moving chromosomes during mitosis is performed by microtubules.
In vitro studies have measured the force produced by bending protofilaments (Grischuk et al., 2005).
Because such forces are too weak, a special device called laser tweezers was used. It creates a highly focused laser beam, thus generating a non-uniform electromagnetic field. Particles entering such a field tend to get to the center. Moreover, the further the particle is from the center, the greater the force acting on it.
Figure 3. Experimental design used to measure the force developed by a microtubule.
To measure the force of depolymerization, a bead was attached to the wall of an artificially created microtubule (with a GTP cap at the end) (Fig. 3). Then, using another laser, the end of the microtubule was cut off, after which the tube began to depolymerize. When the bending ends of the protofilaments reached the bead, it experienced a brief jerk, which was recorded using a quadrant detector (Fig. 4).
Figure 4 - Type of received data
These experiments confirmed the curvature of protofilaments at the end of a contracting microtubule and made it possible to measure the force developed by the protofilaments. During depolymerization, microtubules develop forces sufficient for chromosome movement. The measured force is 30-60 pN per microtubule.
Microtubules are efficient engines: they convert 80-90% of the energy spent on its creation into work to move the ball.
The G1 phase is characterized by the resumption of intensive biosynthesis processes, which during mitosis sharply slows down, and for a short time during cytokinesis, it stops altogether. The total protein content increases continuously during this phase. For most cells, there is a critical point in the G1 phase, the so-called restriction point. During its passage, internal changes occur in the cell, after which the cell must go through all subsequent phases of the cell cycle. The boundary between the S and G2 phases is determined by the appearance of a substance - an S-phase activator.
The G2 phase is considered as the period of preparation of the cell for the onset of mitosis. Its duration is shorter than other periods. In it, the synthesis of fission proteins (tubulin) occurs and phosphorylation of proteins involved in chromatin condensation is observed.
Prophase
During prophase, two parallel processes occur. This is the gradual condensation of chromatin, the appearance of clearly visible chromosomes and disintegration of the nucleolus, as well as the formation of a spindle, which ensures the correct distribution of chromosomes between daughter cells. These two processes are spatially separated by the nuclear envelope, which persists throughout prophase and is destroyed only at its end. The center of microtubule organization in most animal and some plant cells is the cell center or centrosome. In an interphase cell it is located on the side of the nucleus. In the central part of the centrosome there are two centrioles, immersed in its material at right angles to each other. Numerous tubes formed by the protein tubulin extend from the peripheral part of the centrosome. They also exist in the interphase cell, forming a cytoskeleton in it. Microtubules are in a state of very rapid assembly and disassembly. They are unstable and their array is constantly updated. For example, in fibroblast cells in in vitro culture, the average lifetime of microtubules is less than 10 minutes. At the beginning of mitosis, microtubules of the cytoplasm disintegrate, and then their restoration begins. First, they appear in the perinuclear zone, forming a radiant structure - a star. The center of its formation is the centrosome. Microtubules are polar structures because the tubulin molecules from which they are formed are oriented in a certain way. One end of it lengthens three times faster than the others. The fast growing ends are called plus ends, the slow growing ends are called minus ends. Plus the ends are oriented forward in the direction of growth. The centriole is a small cylindrical organelle about 0.2 µm thick and 0.4 µm long. Its wall is formed by nine groups of triplets of tubules. In a triplet, one tube is complete and the two adjacent to it are incomplete. Each triplet is tilted towards the central axis. Adjacent triplets are interconnected by cross-links. New centrioles arise only by duplicating existing ones. This process coincides with the time of DNA synthesis in the S phase. In the G1 period, the centrioles forming a pair move apart by several microns. Then, on each of the centrioles, in its middle part, a daughter centriole is built at a right angle. The growth of daughter centrioles is completed in the G2 phase, but they are still immersed in a single mass of centrosomal material. At the beginning of prophase, each pair of centrioles becomes part of a separate centrosome, from which a radial bundle of microtubules, a star, extends. The formed stars move away from each other on two sides of the nucleus, subsequently becoming the poles of the fission spindle.
Metaphase
Prometaphase begins with the rapid disintegration of the nuclear envelope into membrane fragments indistinguishable from EPS fragments. They are shifted to the cell periphery by chromosomes and spindles. A protein complex is formed at the centromeres of chromosomes, which in electronic photographs looks like a lamellar three-layer structure - a kinetochore. Both chromatids carry one kinetochore; it is to this kinetochore that the protein microtubules of the spindle are attached. Using molecular genetics methods, it was found that the information determining the specific design of kinetochores is contained in the DNA nucleotide sequence in the centromere region. Spindle microtubules attached to chromosome kinetochores play a very important role; firstly, they orient each chromosome relative to the spindle so that its two kinetochores face opposite poles of the cell. Secondly, microtubules move chromosomes so that their centromeres are in the plane of the cell's equator. This process in mammalian cells takes from 10 to 20 minutes and is completed by the end of prometaphase. The number of microtubules associated with each kinetochore varies among species. In humans there are from 20 to 40, in yeast - 1. The plus ends of microtubules are associated with chromosomes. In addition to kinetochore microtubules, the spindle also contains polar microtubules, which extend from opposite poles and are stitched together at the equator by special proteins. Microtubules that extend from the centrosome and are not included in the spindle are called astral; they form a star.
Metaphase. Occupies a significant part of mitosis. It is easily recognized by two features: the bipolar structure of the spindle and the metaphase chromosome plate. This is a relatively stable cell state; many cells can be left in metaphase for several hours or days if they are treated with substances that depolymerize the spindle tubes. Once the agent is removed, the mitotic spindle is able to recover and the cell is able to complete mitosis.
Anaphase
Anaphase begins with the rapid synchronous splitting of all chromosomes into sister chromatids, each of which has its own kinetochore. The splitting of chromosomes into chromatids is associated with DNA replication in the centromere region. Replication of such a small area occurs in a few seconds. The signal to begin anaphase comes from the cytosol and is associated with a short-term rapid increase in the concentration of calcium ions by 10 times. Electron microscopy showed that membrane vesicles rich in calcium accumulate at the spindle poles. In response to the anaphase signal, sister chromatids begin to move towards the poles. This is associated first with the shortening of kinetochore tubes (anaphase A), and then with the moving apart of the poles themselves, associated with the elongation of polar microtubules (anaphase B). The processes are relatively independent, as indicated by their different sensitivity to poisons. In different organisms, the contribution of anaphase A and anaphase B to the final chromosome segregation is different. For example, in mammalian cells, anaphase B begins after anaphase A and ends when the spindle reaches a length 1.5-2 times greater than in metaphase. In protozoa, anaphase B predominates, causing the spindle to lengthen 15 times. Shortening of kinetochore tubes occurs through their depolymerization. Subunits are lost from the plus end, i.e. from the kinetochore side, as a result the kinetochore moves along with the chromosome to the pole. As for pole microtubules. Then in anaphase they assemble and elongate as the poles diverge. By the end of anaphase, the chromosomes are completely separated into two identical groups at the poles of the cell.
Nuclear and cytoplasmic divisions are related. The mitotic spindle plays an important role. In animal cells, already in anaphase, a cleavage furrow appears in the plane of the spindle equator. It is laid at right angles to the long axis of the mitotic spindle. The formation of the furrow is caused by the activity of the contractile ring, which is located under the cell membrane. It consists of the thinnest threads - actin filaments. The contractile ring has sufficient force to bend a thin glass needle inserted into the cell. As the groove deepens, the thickness of the contractile ring does not increase, since some of the filaments are lost as its radius decreases. After cytokinesis is completed, the contractile ring completely disintegrates, and the plasma membrane in the region of the cleavage furrow contracts. For some time, a body of remnants of closely packed microtubules remains in the contact zone of newly formed cells. In plant cells that have a rigid cell wall, the cytoplasm is divided by the formation of a new wall at the border between daughter cells. Plant cells do not have a contractile ring. A phragmoplast is formed in the equatorial plane of the cell, gradually expanding from the center of the cell to its periphery until the growing cell plate reaches the plasma membrane of the mother cell. The membranes fuse, completely separating the resulting cells.
Choose one correct answer. 1. The outer cell membrane ensures a) a constant shape of the cell b) metabolism and energy inb) osmotic pressure in the cell d) selective permeability
2. Cellulose membranes, as well as chloroplasts, do not have cells
a) algae b) mosses c) ferns d) animals
3. In a cell, the nucleus and organelles are located in
a) cytoplasm _ c) endoplasmic reticulum
b) Golgi complex d) vacuoles
4. Synthesis occurs on the membranes of the granular endoplasmic reticulum
a) proteins b) carbohydrates c) lipids d) nucleic acids
5. Starch accumulates in
a) chloroplasts b) nucleus c) leucoplasts d) chromoplasts
6. Proteins, fats and carbohydrates accumulate in
a) nucleus b) lysosomes c) Golgi complex d) mitochondria
7. Participates in the formation of the fission spindle
a) cytoplasm b) cell center c) vacuole d) Golgi complex
8. An organoid consisting of many interconnected cavities, in
which accumulate organic substances synthesized in the cell - these are
a) Golgi complex c) mitochondria
b) chloroplast d) endoplasmic reticulum
9. The exchange of substances between the cell and its environment occurs through
shell due to the presence in it
a) lipid molecules b) carbohydrate molecules
b) numerous holes d) nucleic acid molecules
10. Organic substances synthesized in the cell move to organelles
a) with the help of the Golgi complex c) with the help of vacuoles
b) with the help of lysosomes d) through the channels of the endoplasmic reticulum
11. The breakdown of organic substances in the cell, accompanied by release.
energy and the synthesis of a large number of ATP molecules occurs in
a) mitochondria b) lysosomes c) chloroplasts d) ribosomes
12. Organisms whose cells do not have a formed nucleus, mitochondria,
Golgi complex, belongs to the group
a) prokaryotes b) eukaryotes c) autotrophs d) heterotrophs
13. Prokaryotes include
a) algae b) bacteria c) fungi d) viruses
14. The nucleus plays an important role in the cell, as it is involved in synthesis
a) glucose b) lipids c) fiber d) nucleic acids and proteins
15. Organelle, delimited from the cytoplasm by one membrane, containing
many enzymes that break down complex organic substances
to simple monomers, this
a) mitochondrion b) ribosome c) Golgi complex d) lysosome
Please help A1. Attachment of the spindle threads occurs: in 1) interphase 2) prophase 3) metaphase 4) anaphase. A2. Mitosis does not occur in prophasedit: 1) dissolution of the nuclear membrane 2) formation of the fission spindle 3) doubling of DNA 4) dissolution of the nucleoli. A3) in animals, during the process of mitosis, in contrast to meiosis, the following cells are formed: 1) somatic 2) with half the set of chromosomes 3) sexual 4) spore. A4) divergence of chromotides to the cell poles occurs in: 1) prophase of the first meiotic division 2) prophase of the second meiotic division 3) interphase before the first division 4) interphase before the second division
1. Starchaccumulates in
A
– chloroplasts B – nucleus C – leukoplasts D – chromoplasts
2. Cytoplasm does not perform
function
A
– movement of substances B – interaction of all organelles
IN
– power supply G – protective
3. Spares
nutrients and breakdown products accumulate in plant cells in
A
– lysosomes B – chloroplasts C – vacuoles D – nucleus
4. Proteins,
fats and carbohydrates are oxidized to release energy in
A
– mitochondria B – leukoplasts
IN
– endoplasmic reticulum G – Golgi complex
5. "Assembly"
ribosome occurs in
A
– endoplasmic reticulum B - Golgi complex
IN
– cytoplasm D – nucleoli
6. On the surface of the smooth endoplasmic reticulum, molecules are synthesized: A – mineral salts B – nucleotides C – carbohydrates, lipids D – proteins
7. On the surface of the rough endoplasmic reticulum are located A – lysosomes B – microtubules C – mitochondria D – ribosomes
8. Eukaryotes are organisms that have A – plastids B – flagella C – cell wall D – formed nucleus
9. The cell is the basic unit of structure of all organisms, since A - the reproduction of organisms is based on cell division B - metabolic reactions take place in the cell C - cell division is the basis of the growth of the organism D - all organisms consist of cells
10. A – cytoplasm B – cell center C – endoplasmic reticulum D – vacuole is involved in the formation of the division spindle