Chromosome is its structure. Chromosomes: structure, function and abnormalities

Chromosomes are an intensely colored body, consisting of a DNA molecule associated with histone proteins. Chromosomes are formed from chromatin at the beginning of cell division (in the prophase of mitosis), but it is better to study them in the metaphase of mitosis. When chromosomes are located in the equatorial plane and are clearly visible under a light microscope, the DNA in them reaches maximum spiralization.

Chromosomes consist of 2 sister chromatids (doubled DNA molecules) connected to each other in the region of the primary constriction - the centromere. The centromere divides the chromosome into 2 arms. Depending on the location of the centromere, chromosomes are subdivided into:

    the metacentric centromere is located in the middle of the chromosome and its arms are equal;

    submetacentric centromere is displaced from the middle of chromosomes and one arm is shorter than the other;

    acrocentric - the centromere is located close to the end of the chromosome and one arm is much shorter than the other.

In some chromosomes, there are secondary constrictions that separate from the shoulder of the chromosome a section called a satellite, from which a nucleolus is formed in the interphase nucleus.

Chromosome rules

1. The constancy of the number. The somatic cells of the organism of each species have a strictly defined number of chromosomes (in humans - 46, in cats - 38, in fruit fly - 8, in dogs - 78, in chicken - 78).

2. Pairing. Each chromosome in somatic cells with a diploid set has the same homologous (identical) chromosome, identical in size, shape, but unequal in origin: one from the father, the other from the mother.

3. Individuality. Each pair of chromosomes differs from the other pair in size, shape, alternating light and dark stripes.

4. Continuity. Before cell division, the DNA is doubled and the result is 2 sister chromatids. After division, one chromatid enters the daughter cells and, thus, the chromosomes are continuous - a chromosome is formed from the chromosome.

All chromosomes are subdivided into autosomes and sex chromosomes. Autosomes are all chromosomes in cells, with the exception of sex chromosomes, there are 22 pairs of them. Sexual - this is the 23rd pair of chromosomes, which determines the formation of the male and female body.

In somatic cells there is a double (diploid) set of chromosomes, in sex cells - a haploid (single) set.

A certain set of chromosomes of a cell, characterized by the constancy of their number, size and shape, is called karyotype.

In order to understand a complex set of chromosomes, they are arranged in pairs as their size decreases, taking into account the position of the centromere and the presence of secondary constrictions. This systematized karyotype is called an idiogram.

For the first time, such a systematization of chromosomes was proposed at the Congress of Genetics in Denver (USA, 1960)

In 1971, in Paris, chromosomes were classified according to the color and alternation of dark and light bands of hetero- and euchromatin.

To study the karyotype of genetics, the method of cytogenetic analysis is used, in which it is possible to diagnose a number of hereditary diseases associated with a violation of the number and shape of chromosomes.

1.2. Cell life cycle.

The life of a cell from the moment it emerges as a result of division until its own division or death is called the life cycle of a cell. Throughout life, cells grow, differentiate and perform specific functions.

The life of a cell between divisions is called interphase. Interphase consists of 3 periods: presynthetic, synthetic and postsynthetic.

The presynthetic period immediately follows the division. At this time, the cell grows intensively, increasing the number of mitochondria and ribosomes.

During the synthetic period, replication (doubling) of the amount of DNA occurs, as well as the synthesis of RNA and proteins.

In the postsynthetic period, the cell stores energy, proteins of the achromatin spindle are synthesized, and preparations for mitosis are underway.

There are different types of cell division: amitosis, mitosis, meiosis.

Amitosis is a direct division of prokaryotic cells and some cells in humans.

Mitosis is an indirect cell division, during which chromosomes are formed from chromatin. Through mitosis, somatic cells of eukaryotic organisms divide, as a result of which the daughter cells receive exactly the same set of chromosomes as the daughter cell had.

Mitosis

Mitosis consists of 4 phases:

    Prophase is the initial phase of mitosis. At this time, DNA spiralization and the shortening of chromosomes begin, which, from thin invisible chromatin filaments, become short thick ones, visible under a light microscope, and are arranged in the form of a ball. The nucleolus and the nuclear envelope disappear, and the nucleus disintegrates, the centrioles of the cell center diverge along the poles of the cell, and the spindle threads stretch between them.

    Metaphase - chromosomes move towards the center, spindle threads are attached to them. Chromosomes are located in the equatorial plane. They are clearly visible under a microscope and each chromosome consists of 2 chromatids. In this phase, the number of chromosomes in the cell can be counted.

    Anaphase - sister chromatids (which appeared in the synthetic period with DNA duplication) diverge to the poles.

    Telophase (Greek telos - end) is opposite to prophase: chromosomes from short thick visible ones become thin long ones invisible under a light microscope, the nuclear membrane and nucleolus are formed. The telophase ends with the division of the cytoplasm with the formation of two daughter cells.

The biological significance of mitosis is as follows:

    daughter cells receive exactly the same set of chromosomes that the mother cell had, therefore, a constant number of chromosomes is maintained in all cells of the body (somatic).

    all cells are divided, except for reproductive cells:

    the body grows in the embryonic and postembryonic periods;

    all functionally obsolete cells of the body (epithelial cells of the skin, blood cells, cells of the mucous membranes, etc.) are replaced with new ones;

    processes of regeneration (restoration) of lost tissues occur.

Mitosis scheme

Under the influence of unfavorable conditions on a dividing cell, the spindle of division can unevenly stretch the chromosomes to the poles, and then new cells with a different set of chromosomes are formed, pathology of somatic cells (heteroploidy of autosomes) arises, which leads to diseases of tissues, organs, and the body.

Chromosomes - self-reproducing structures of the cell nucleus. In both prokaryotic and eukaryotic organisms, genes are arranged in groups on individual DNA molecules, which, with the participation of proteins and other cell macromolecules, are organized into chromosomes. Mature cells of the germ line (gametes - eggs, sperm) of multicellular organisms contain one (haploid) set of chromosomes of the organism.

After the complete sets of chromatids move to the poles, they are called chromosomes... Chromosomes are structures in the nucleus of eukaryotic cells that spatially and functionally organize DNA in the genome of individuals.

Chemical composition of chromosomes. A chromosome is a deoxyribonucleoprotein (DNP), that is, a complex formed from one continuous double-stranded DNA molecule and proteins (histones and non-histones). Chromosomes also include lipids and minerals (for example, Ca 2+, Mg 2+ ions).

Each chromosome - complex supramolecular formation formed as a result of chromatin compaction.

Chromosome structure. In most cases, chromosomes are clearly visible only in dividing cells starting from the metaphase stage, when they can be seen even under a light microscope. During this period, it is possible to determine the number of chromosomes in the nucleus, their size, shape and structure. It is these chromosomes that are called metaphase. Interphase chromosomes are often referred to simply as chromatin.

The number of chromosomes is usually constant for all cells of an individual of any species of plants, animals and humans. But have different types the number of chromosomes is not the same (from two to several hundred). The horse roundworm has the smallest number of chromosomes, the largest is found in protozoa and ferns, which are characterized by high levels of polyploidy. Typically, diploid sets contain from one to several dozen chromosomes.

The number of chromosomes in the nucleus is not related to the level of evolutionary development of living organisms. In many primitive forms it is large, for example, the nuclei of some protozoan species contain hundreds of chromosomes, while chimpanzees have only 48 of them.

Each chromosome formed by one DNA molecule is elongated rod-shaped structure - chromatid with two "shoulders" separated by a primary constriction, or centromere. The metaphase chromosome consists of two sister chromatids connected by a centromere, each of which contains one DNA molecule arranged in a spiral.

Centromere Is a small fibrillar body that carries out the primary constriction of the chromosome. It is the most important part of the chromosome, as it determines its movement. The centromere, to which the spindle threads are attached during division (during mitosis and meiosis), is called kinetochore(from the Greek kinetos - mobile and choros - place). It controls the movement of diverging chromosomes during cell division. A chromosome devoid of a centromere is unable to perform ordered movement and can be lost.

Usually, the centromere of a chromosome occupies a certain place, and this is one of the species characteristics by which chromosomes are distinguished. A change in the position of the centromere in a particular chromosome serves as an indicator of chromosomal rearrangements. The shoulders of the chromosomes end in sections that are not able to connect with other chromosomes or their fragments. These ends of the chromosomes are called telomeres... Telomeres protect the ends of chromosomes from sticking together and thereby ensure the preservation of their integrity. For the discovery of the mechanism of protection of chromosomes by telomeres and the enzyme telomerase, American scientists E. Blackburn, K. Greider and D. Shostak in 2009 were awarded Nobel Prize in the field of medicine and physiology. The ends of chromosomes are often enriched heterochromatin.


Depending on the location of the centromere, three main types of chromosomes are determined: equal arms (shoulders of equal length), unequal arms (with shoulders of different lengths) and rod-shaped (with one, very long and another, very short, barely noticeable shoulder). Some chromosomes have not only one centromere, but also a secondary constriction that is not associated with attachment of the spindle filament during division. This site - nucleolar organizer, which performs the function of synthesizing the nucleolus in the nucleus.

Replication of chromosomes

An important property of chromosomes is their ability to duplicate (self-replicate). Usually, the duplication of chromosomes precedes cell division. The duplication of chromosomes is based on the process of replication (from Latin replicatio - repetition) of DNA macromolecules, which ensures accurate copying of genetic information and its transmission from generation to generation. Duplication of chromosomes is a complex process that involves not only the replication of giant DNA molecules, but also the synthesis of DNA-bound chromosomal proteins. The final stage is the packaging of DNA and proteins into special complexes that form a chromosome. As a result of replication, instead of one maternal chromosome, two identical daughter chromosomes appear.

Chromosome function consists of:

  • in the storage of hereditary information. Chromosomes are carriers of genetic information;
  • transfer of hereditary information. Hereditary information is transmitted by replication of the DNA molecule;
  • implementation of hereditary information. Due to the reproduction of one or another type of i-RNA and, accordingly, one or another type of protein, control over all vital processes of the cell and the whole organism is carried out.

Thus, chromosomes with genes enclosed in them determine a continuous reproduction sequence.

Chromosomes carry out complex coordination and regulation of processes in the cell due to the contained genetic information, which ensures the synthesis of the primary structure of protein-enzymes.

Each species has a certain number of chromosomes in its cells. They are carriers of genes that determine the hereditary properties of cells and organisms of the species. Gene- This is a section of the DNA molecule of the chromosome, on which various RNA molecules (translators of genetic information) are synthesized.

In somatic, that is, bodily, cells usually contain a double, or diploid, set of chromosomes. It consists of pairs (2n) of chromosomes that are almost identical in shape and size. Such paired, similar to each other chromosome sets are called homologous (from the Greek homos - equal, identical, common). They come from two organisms; one set from the mother and the other from the father. Such a paired set of chromosomes contains all the genetic information of a cell and an organism (individual). Homologous chromosomes are the same in shape, length, structure, centromere location and carry the same genes with the same localization. They contain the same set of genes, although they may differ in their alleles. Thus, homologous chromosomes contain very similar, but not identical, hereditary information.

The set of signs of chromosomes (their number, size, shape and details of the microscopic structure) in the cells of the body of an organism of one type or another is called karyotype. The shape of chromosomes, their number, size, location of the centromere, and the presence of secondary constrictions are always specific for each species; they can be used to compare the kinship of organisms and establish their belonging to one or another species.

The constancy of the karyotype characteristic of each species was developed in the process of its evolution and is conditioned by the laws of mitosis and meiosis. However, during the existence of a species in its karyotype due to mutations, changes in chromosomes can occur. Some mutations significantly change the hereditary qualities of the cell and the organism as a whole.

Constant characteristics of the chromosome set - the number and morphological features of chromosomes, determined mainly by the location of centromeres, the presence of secondary constrictions, alternation of euchromatin and heterochromatin regions, etc., make it possible to identify species. Therefore, the karyotype is called "Passport" of the type.

CHROMOSOMES CHROMOSOMES

(from chromo ... and soma), organelles of the cell nucleus, which are carriers of genes and determine inheritance, the properties of cells and organisms. They are capable of self-reproduction, possess a structural and functional individuality and retain it for generations. The term "X." proposed by W. Waldeyer (1888). The basis of X. is one continuous double-stranded DNA molecule (in X. about 99% of the DNA of the cell), bound with proteins (histones, etc.) in a nucleoprotein. The structure of the DNA molecule, its genetic. the code ensures the recording of inheritances, information in X., proteins (in X. higher plants and animals contain up to 65% of them) take part in the complex packaging of DNA in X. and the regulation of its ability to synthesize RNA - transcription. In the process of functioning, X. undergo structural and morphological. transformation, which is based on the process of spiralization - despiralization of structural subunits of X. - chromonema. At the metaphase stage of cell division, spiralized (close-packed) X. are well distinguishable in a light microscope. Each X. consists of two longitudinal copies - chromatids, formed during reduplication and held together by a centromere. In the cells of the body of bisexual animals and plants, each X. is represented by two so-called. homologous X., originating one from the maternal, and the other from the paternal organism. Sex cells formed as a result of meiosis contain only one of the two homologous X. The number of X. varies greatly: from two to several. hundreds of X. make up chromosome sets (see KARYOTYPE) of different species. Each type of organism has a characteristic and constant set of chromosomes in the cell, fixed in the evolution of this species, and its changes occur only as a result of mutations. In the karyotype, there are sexual X., autosomes, nucleolar-forming X .; some species may have additional X., the number of which is not constant and does not contain genes characteristic of this species. In the process of development of multicellular organisms, X. can acquire a peculiar form and in some cases have specials. name, e.g. polytene X. type of lamp brushes, etc. To genetic. apparatus of bacteria and viruses (they usually contain one linear or circular X. in X. not only a complex of biopolymers, but also specific. supramolecular structure. (see REPLICATION).


.(Source: "Biological Encyclopedic Dictionary." - M .: Sov.Encyclopedia, 1986.)

chromosomes

The oblong bodies located in the cell nucleus, enclosing genes... Chromosomes are the main carriers of genetic material, ensuring its transmission from generation to generation.
In the period between cell divisions (in the interphase mitosis) chromosomes are invisible under a light microscope and are represented by untwisted (despiralized) threads chromatin... During this period, an important genetic event occurs - replication DNA and the duplication of chromosomes based on it. As long as the two resulting copies are held together by the centromere, they are called sister copies. chromatids... With the onset of cell division, chromosomes spiralize and condense. In a light microscope, it becomes clear that they consist of two chromatids. During mitosis, chromatids are separated and become independent chromosomes. Thus, in the course of the cell cycle, the structure of the chromosomes undergoes changes.
Each chromosome is individual, i.e. characterized only by its size, shape and position of the centromere. In the cells of the body of sexually reproducing organisms, any chromosome is represented by two copies, or homologues (see. Diploid). With the formation of germ cells in meiosis each of them contains one of two homologous chromosomes (see. Haploid). During fertilization, the pairing of homologous chromosomes is restored: one chromosome of each pair is paternal, the other is maternal.
The set of signs of the chromosome set (the number of chromosomes, their size and shape) is constant for cells of each species and is called it karyotype... In the karyotype, a pair of determining the sex of the organism is distinguished sex chromosomes and all other chromosomes are autosomes. The study of the behavior of chromosomes in mitosis and meiosis, as well as the role of chromosomes, especially sex chromosomes, in the transmission of characters from one generation to another led to the creation in the beginning. 20th century chromosomal theory of heredity... The chromosome is often called the genetic material of bacteria and viruses, although its structure differs from the chromosomes of eukaryotic organisms.

.(Source: "Biology. Modern illustrated encyclopedia." Ed. A. P. Gorkin; Moscow: Rosmen, 2006.)


See what "CHROMOSOMES" are in other dictionaries:

    - [Dictionary foreign words Russian language

    - (from chromo ... and Greek soma body) structural elements of the cell nucleus, containing DNA, which contains the hereditary information of the organism. Genes are arranged in a linear order on chromosomes. Self-doubling and regular distribution of chromosomes over ... ... Big Encyclopedic Dictionary

    CHROMOSOMES, structures that carry genetic information about the body, which is contained only in the nuclei of cells of Eucariotes. Chromosomes are filamentous, they consist of DNA and have a specific set of GENES. Each type of organism has a characteristic ... ... Scientific and technical encyclopedic dictionary

    Chromosomes- Structural elements of the cell nucleus, containing DNA, which contains the hereditary information of the organism. Genes are arranged in a linear order on chromosomes. Each human cell contains 46 chromosomes, divided into 23 pairs, of which 22 ... ... Big psychological encyclopedia

    Chromosomes- * chramasomes * chromosomes self-reproducing elements of the cell nucleus that retain their structural and functional individuality and are stained with basic dyes. They are the main material carriers of hereditary information: genes ... ... Genetics. encyclopedic Dictionary

    CHROMOSOMES, ohm, units. chromosome, s, wives. (specialist.). A permanent component of the nucleus of animal and plant cells, carriers of hereditary genetic information. | adj. chromosomal, oh, oh. H. set of cells. Chromosomal theory of heredity. ... ... Dictionary Ozhegova

    chromosomes- - structural elements of the cell nucleus containing genes organized in a linear order ... A Brief Dictionary of Biochemical Terms

    CHROMOSOMES- CHROMOSOMES, the most important component of the nucleus, which is sharply revealed in the process of karyokinesis due to its ability to be intensely stained with basic colors. The collection of modern biol. data forces to view X. as carriers ... ... Great medical encyclopedia

    Scheme of the structure of the chromosome in the late prophase metaphase of mitosis. 1 chromatid; 2 centromeres; 3 short shoulder; 4 long shoulder. Human chromosome set (karyotype) (female). Chromosomes (Greek χρώμα color and ... Wikipedia

    - (from Chromo ... and Soma organelles of the cell nucleus, the totality of which determines the main hereditary properties of cells and organisms. A complete set of X. in a cell, characteristic of this organism, called the Karyotype. In any cell of the body ... ... Great Soviet Encyclopedia

Books

  • Praise for the stupidity of the chromosome. Confessions of a Rebellious Molecule, Lima de Faria Antonio, The publication contains the latest data on the molecular organization of chromosomes. The information is presented in the form of small thematic stories; carefully selected colorful ... Category: Biology Publisher: Binom. Knowledge laboratory, Manufacturer:

For this reason, they reach large sizes, which is inconvenient in the process of cell division. To prevent the loss of genetic information, nature invented chromosomes.

Chromosome structure

These dense structures are rod-shaped. Chromosomes differ from each other in length, which ranges from 0.2 to 50 microns. The width usually has a constant value and does not differ for different pairs of dense bodies.

At the molecular level, chromosomes are a complex complex of nucleic acids and histone proteins, the ratio of which is 40% to 60% by volume, respectively. Histones are involved in the compaction of DNA molecules.

It should be noted that a chromosome is a fickle structure of the nucleus of a eukaryotic cell. Such bodies are formed only during the period of division, when it is necessary to package all the genetic material to facilitate its transfer. Therefore, we consider the structure of the chromosome at the time of preparation for mitosis / meiosis.

The primary constriction is a fibrillar body that divides the chromosome into two arms. Depending on the ratio of the length of these arms, chromosomes are distinguished:

  1. Metacentric when the primary constriction is exactly centered.
  2. Submetacentric: the length of the shoulders differs slightly.
  3. In acrocentric ones, the primary constriction is strongly displaced to one of the ends of the chromosome.
  4. Telocentric, when one of the shoulders is completely absent (do not occur in humans).

Another feature of the structure of the chromosome of a eukaryotic cell is the presence of a secondary constriction, which is usually strongly displaced towards one of the ends. Its main function is to synthesize ribosomal RNAs on the DNA matrix, which then form non-membrane organelles of the ribosome cell. Secondary constrictions are also called nucleolar organizers. These formations are located at the distal chromosome.

Several organizers form an integral structure - the nucleolus. The number of such formations in the nucleus can vary from 1 to several dozen, and they are usually seen even in a light microscope.

During the synthetic phase of mitosis, the structure of the chromosome changes as a result of DNA duplication during replication. At the same time, a familiar shape is formed, reminiscent of the letter X. It is in this form that you can often find chromosomes and make a high-quality picture on special microscopes.

It should be noted that the number of chromosomes in different species does not in any way indicate the degree of their evolutionary development. Here are some examples:

  1. A person has 46 chromosomes.
  2. The cat has 60.
  3. The crucian has 100.
  4. The rat has 42.
  5. Bow has 16.
  6. Drosophila fly has 8.
  7. The mouse has 40.
  8. Corn has 20.
  9. Apricot has 16.
  10. Crab 254.

Chromosome functions

The nucleus is the central structure of any eukaryotic cell, since it contains all the genetic information. Chromosomes perform a number of important functions, namely:

  1. Storing the actual genetic information unchanged.
  2. Transfer of this information by replication of DNA molecules during cell division.
  3. The manifestation of characteristic features of the body due to the activation of genes responsible for the synthesis of certain proteins.
  4. Assembly of rRNA in nucleolar organizers for the construction of small and large ribosome subunits.

An important role in cell division is assigned to the primary constriction, to the proteins of which the fission spindle filaments are attached in the metaphase of mitosis or meiosis. In this case, the X-structure of the chromosome is broken into two rod-shaped bodies, which are delivered to different poles and will be further enclosed in the nuclei of daughter cells.

Compaction levels

The first level is called nucleosomal. In this case, the DNA is wrapped around the histone proteins, forming "beads on a string."

The second level is nucleomeric. Here, the "beads" come together and form filaments up to 30 nm thick.

The third level is called chromomeric. In this case, the threads begin to form loops of several orders, thereby shortening the initial length of DNA many times.

The fourth level is lame. Compaction reaches its maximum, and the resulting rod-shaped formations are already visible in the light microscope.

Features of the genetic material of prokaryotes

A distinctive feature of bacteria is the absence of a nucleus. Genetic information is also stored by DNA, which are scattered throughout the cell as part of the cytoplasm. Among the nucleic acid molecules, one ring will stand out. It is usually located in the center and is responsible for all the functions of the prokaryotic cell.

Sometimes this DNA is called the chromosome of a bacterium, the structure of which, of course, does not coincide in any way with that of a eukaryote. Therefore, this comparison is relative and simply simplifies the understanding of some biochemical mechanisms.

Today we will together analyze an interesting question concerning the biology of the school course, namely: the types of chromosomes, their structure, functions performed, and so on.

First you need to understand what it is, a chromosome? It is customary to call the structural elements of the nucleus in eukaryotic cells. It is these particles that contain DNA. The latter contains hereditary information that is transmitted from the parent organism to descendants. This is possible with the help of genes (structural units of DNA).

Before we take a closer look at the types of chromosomes, it is important to familiarize yourself with some questions. For example, why are they named with this particular term? Back in 1888, such a name was given to them by the scientist V. Valdeyer. If translated from Greek, then literally we get the color and body. What is the reason for this? You can find out in the article. Very interesting is the fact that it is customary to call circular DNA in bacteria chromosomes. This is despite the fact that the structure of the latter and the chromosomes of eukaryotes is very different.

Story

So, it became clear to us that the chromosome is called the organized structure of DNA and protein, which is contained in cells. It is very interesting that one piece of DNA contains a lot of genes and other elements that encode all the genetic information of an organism.

Before considering the types of chromosomes, we propose to talk a little about the history of the development of these particles. And so, the experiments that the scientist Theodore Boveri began to conduct in the mid-1880s demonstrated the relationship between chromosomes and heredity. At the same time, Wilhelm Roux put forward the following theory - each chromosome has a different genetic load. This theory was tested and proven by Theodore Boveri.

Thanks to the work of Gregor Mendel in the 1900s, Boveri was able to trace the relationship between the rules of inheritance and the behavior of chromosomes. Boveri's discoveries were able to influence the following cytologists:

  • Edmund Beecher Wilson.
  • Walter Sutton.
  • Theophilus Painter.

Edmund Wilson's work was to link the Boveri and Sutton theories, which is described in the book The Cell in Development and Heredity. The work was published around 1902 and focused on the chromosomal theory of heredity.

Heredity

And another minute of theory. In his writings, the researcher Walter Sutton was able to find out how much chromosomes are still contained in the cell nucleus. It was said earlier that the scientist considered these particles to be carriers of hereditary information. In addition, Walter found out that all chromosomes are made up of genes, so they are precisely the culprits in the fact that parental properties and functions are passed on to descendants.

In parallel, work was carried out by Theodore Boveri. As stated earlier, both scholars investigated a number of questions:

  • transmission of hereditary information;
  • formulation of the main provisions on the role of chromosomes.

This theory is now called the Boveri-Sutton theory. Its further development was carried out in the laboratory of the American biologist Thomas Morgan. Together, scientists were able to:

  • to establish patterns of distribution of genes in these structural elements;
  • develop a cytological base.

Structure

In this section, we propose to consider the structure and types of chromosomes. So, we are talking about structural cells that store and transmit hereditary information. What are chromosomes made of? From DNA and protein. In addition, the constituent parts of the chromosomes form chromatin. At the same time, proteins play an important role for DNA packaging in the cell nucleus.

The diameter of the nucleus does not exceed five microns, and the DNA is packed completely into the nucleus. So DNA in the nucleus has a loop structure that proteins support. At the same time, the latter recognize the nucleotide sequences for their convergence. If you are going to study the structure of chromosomes under a microscope, then the best time for this is the metaphase of mitosis.

The chromosome has the shape of a small rod, which consists of two chromatids. The latter are held by the centromere. It is also very important to note that each individual chromatid consists of chromatin loops. All chromosomes can be in one of two states:

  • active;
  • inactive.

Forms

We will now look at the existing types of chromosomes. In this section, you can find out what forms of these particles exist.

All chromosomes have their own individual structure. A distinctive feature is the coloring features. If you are studying chromosome morphology, then there are some significant things worth paying attention to:

  • location of the centromere;
  • length and position of the shoulders.

So, there are the following main types of chromosomes:

  • metacentric chromosomes (their distinctive feature- the location of the centromere in the middle, this form is also called equal-arm);
  • submetacentric (a distinctive feature is the displacement of the waist to one side, another name is unequal arms);
  • acrocentric (a distinctive feature is the presence of a centromere practically at one of the ends of the chromosome, another name is rod-shaped);
  • dotted (they got this name due to the fact that their shape is very difficult to determine, which is associated with their small size).

Functions

Regardless of the type of chromosomes in humans and other creatures, these particles carry out a mass different functions... You can read about what we are talking about in this section of the article.

  • In the storage of hereditary information. Chromosomes are carriers of genetic information.
  • In the transmission of hereditary information. Hereditary information is transmitted by replication of the DNA molecule.
  • In the implementation of hereditary information. Due to the reproduction of one or another type of i-RNA, and, accordingly, one or another type of protein, control over all vital processes of the cell and the whole organism is carried out.

DNA and RNA

We looked at what types of chromosomes exist. We now turn to a detailed study of the question of the role of DNA and RNA. It is very important to note that it is nucleic acids that make up about five percent of the cell mass. They appear to us as mononucleotides and polynucleotides.

There are two types of these nucleic acids:

  • DNA, which stands for deoxyribonucleic acid;
  • RNA, decoding - ribonucleic acids.

In addition, it is important to remember that these polymers are composed of nucleotides, that is, monomers. These monomers in both DNA and RNA are basically structurally similar. Each individual nucleotide also consists of several components, or rather, three, interconnected by strong bonds.

Now a little about the biological role of DNA and RNA. To begin with, it is important to note that three types of RNA can be found in a cell:

  • informational (removing information from DNA, acting as a matrix for protein synthesis);
  • transport (transfers amino acids for protein synthesis);
  • ribosomal (participates in protein biosynthesis, the formation of the structure of the ribosome).

What is the role of DNA? These particles store information of heredity. Parts of this chain contain a special sequence of nitrogenous bases, which are responsible for hereditary traits. In addition, the role of DNA is in the transmission of these traits in the process of cell division of nuclei. With the help of RNA, RNA is synthesized in cells, due to which proteins are synthesized.

Chromosome set

So, we are considering the types of chromosomes, sets of chromosomes. We pass on to a detailed consideration of the issue concerning the chromosome set.

The number of these elements is characteristic feature species. Take the fruit fly as an example. She has a total of eight, while the primates have forty-eight. The human body has forty-six chromosomes. We immediately draw your attention to the fact that their number is the same for all cells of the body.

In addition, it is important to understand that there are two possible types of chromosomes:

  • diploid (characteristic of eukaryotic cells, is a complete set, that is, 2n are present in somatic cells);
  • haploid (half of the complete set, that is, n, are present in the germ cells).

You need to know that chromosomes form pairs, the representatives of which are homologues. What does this term mean? Homologous chromosomes are called chromosomes that have the same shape, structure, centromere location, and so on.

Sex chromosomes

Now we will take a closer look at the next type of chromosome - sex. It is not one, but a pair of chromosomes, different in males and females of the same species.

As a rule, one of the organisms (male or female) is the owner of two identical, fairly large X chromosomes, with the genotype being XX. An individual of the opposite sex has one X chromosome and a slightly smaller Y chromosome. In this case, the genotype is XY. It is also important to note that in some cases the formation of a male sex occurs in the absence of one of the chromosomes, that is, the X0 genotype.

Autosomes

These are paired particles in organisms with a chromosomal sex determination are the same for both males and females. Simply put, all chromosomes (except sex) are autosomes.

Please note that the presence, copies and structure does not depend in any way on the sex of the eukaryotes. All autosomes have a sequential number. If you take a person, then twenty-two pairs (forty-four chromosomes) are autosomes, and one pair (two chromosomes) are sex chromosomes.

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