Types of metaphase chromosomes, their structure. There are four types of chromosome structure: telocentric(rod-shaped chromosomes with a centromere located at the proximal end); acrocentric(rod-shaped chromosomes with a very short, almost imperceptible second arm);

submetacentric(with shoulders of unequal length, resembling the letter L in shape); metacentric(V-shaped chromosomes with arms of equal length). The chromosome type is constant for each homologous chromosome and can be constant in all representatives of the same species or genus.

Chromosomes are synthetically inactive. The structure of chromosomes is best studied

at the moment of their greatest condensation, i.e. in metaphase and the beginning of anaphase of mitosis.

Each chromosome in the metaphase of mitosis consists of two chromatids,

formed as a result of reduplication, and connected by a centromere

(primary constriction). In the central part of the centromere are kinetochores, to which microtubules of spindle filaments are attached during mitosis. In anaphase, the chromatids are separated from each other. Daughter chromosomes containing the same genetic information are formed from them. The centromere divides the chromosome into two arms. Chromosomes with equal arms are called equal arms or metacentric, with arms of unequal length - unequal arms - submetacentric, with one short and the second almost imperceptible - rod-shaped or acrocentric (Fig. 48).

Some chromosomes have a secondary constriction that separates the satellite.

Secondary constrictions are called nucleolar organizers. In them in the interphase

nucleolus is formed. The nucleolar organizers contain DNA responsible for the synthesis of rRNA. The arms of chromosomes terminate in regions

called telomeres, unable to connect with other chromosomes.

Number, size and shape of chromosomes in a set different types may vary.

The set of features of a chromosome set is called a karyotype.

The chromosome set is specific and constant for individuals of each species. At

a human has 46 chromosomes, a mouse has 40 chromosomes, etc. In somatic cells with a diploid set of chromosomes, the chromosomes are paired. They are called homologous. One chromosome in a pair comes from the mother's organism, the other from the father's. Changes in the structure of chromosomes or in their number result from mutations. Each pair of chromosomes in a set is individual. Chromosomes from different pairs are called non-homologous.

pharynx. There are numerous digestive vacuoles in the cytoplasm, and powder is located at the posterior end of the body. There are two contractile vacuoles. The micronucleus closely adjoins the large macronucleus. Ciliates are capable of encysting. The ciliates themselves and their cysts can long time maintain viability outside the host organism. V tap water ciliates survive up to 7 days. Cysts remain alive in a humid environment (at room temperature) for up to two months. Balantidia is localized in the large (sometimes in the small) intestine in humans, causing ulceration of its walls. Clinically, this severe disease is expressed in bloody diarrhea, colic, fever and muscle weakness. The main source of distribution of balantidiasis are pigs infected with balantidia. Balantidia form cysts in the intestines of pigs, which enter the intestine with faeces. external environment and stay there for a long time. Human infection occurs when cysts are introduced into the digestive tract with dirty hands or food.

Often balantidiasis affects people associated with care work.

pigs or with pork processing. Diagnosis is made by finding balantidia in feces.

Ticket 11 Implementation of genetic information in the cell. Regulation of gene activity in pro- and eukaryotes. 2. Ontogeny, its periodization. Morpho-functional and genetic features of germ cells.

The implementation of genetic information is a process that occurs within eachliving cell, during whichgenetic information, written inDNA, is embodied in biologically active substances -RNAandsquirrels. The transfer of genetic information from DNA to RNA and from RNA to protein is universal for all cellular organisms without exception. The concept of this information flow is called the central dogma of molecular biology. The principle scheme for the implementation of genetic information in pro- and eukaryotes.
PROKARYOTES. Atprokaryotessynthesissquirrel ribosome(broadcast) is not spatially separated fromtranscriptionsand can occur even before the completion of the synthesismRNA RNA polymerase. Prokaryotic mRNAs are often polycistronic, that is, they contain several independentgenes.
EUKARYOTES. mRNAeukaryoteis synthesized as a precursor, pre-mRNA, which then undergoes complex staged maturation -processing, including joiningcap-structures to5" - the end of the molecule, the attachment of several tens of residuesadenineto her3" -end (polyadenylation), splitting out insignificant areas -intronsand connecting significant areas with each other -exons(splicing). In this case, the connection of exons of the same pre-mRNA can take place different ways, leading to the formation of different mature mRNAs, and ultimately different options protein (alternative splicing). Only successfully processed mRNA is exported from the nucleus to the cytoplasm and involved in translation.

2. Ontogeny - individual development individuals - starts from the moment of merger

sperm with egg and the formation of a zygote, ends in death.

The intrauterine form is characteristic of mammals and humans. Everything

the functions of the fetus are carried out at the expense of the mother's body, with the help of

special organ - the placenta.

The egg is a large immobile cell with a reserve nutrients. The size of the female egg is 150–170 microns (much larger than male spermatozoa, which are 50–70 microns in size). The functions of nutrients are different. They are performed:

1) components needed for protein biosynthesis processes (enzymes, ribosomes, m-RNA, t-RNA and their precursors);

2) specific regulatory substances that control all processes that occur with the egg, for example, the disintegration factor of the nuclear membrane

3) the yolk, which includes proteins, phospholipids, various fats, mineral salts. The ovum is usually spherical or slightly elongated shape, contains a set of those typical organelles as any cell. Like other cells, the egg is delimited by a plasma membrane, but on the outside it is surrounded by a shiny shell consisting of mucopolysaccharides (got its name for its optical properties). The zona pellucida is covered with a radiant crown, or follicular membrane, which is the microvilli of follicular cells. It plays a protective role, nourishes the egg. The egg is devoid of an apparatus for active movement. For 4–7 days, it passes through the oviduct to the uterine cavity, a distance that is approximately 10 cm. Plasma segregation is characteristic of the egg. This means that after fertilization in an egg that is not yet crushed, such uniform distribution cytoplasm, that in the future, the cells of the rudiments of future tissues receive it in a certain regular amount.

Similar information.

Introduction

DNA molecules in eukaryotic cells are very large. Thus, the length of DNA molecules isolated from human cells reaches several centimeters. It is generally accepted that each eukaryotic chromosome contains one single continuous DNA molecule. Taking into account the species number of chromosomes in mammals, we can say that, on average, they have about 2 m of DNA per interphase nucleus, which is located in a spherical nucleus with a diameter of less than 10 μm. At the same time, a certain order of arrangement of DNA molecules must be preserved in the nucleus in order to ensure its ordered functioning.

That is why DNA molecules in the nuclei of eukaryotic cells are always in complex with proteins in the composition of chromatin, which is formed from chromosomes after the end of nuclear division as a result of complex process unwinding (despiralization) of chromosomes.

Exploring structural organization chromatin and chromosomes, one can definitely speak of several levels of DNA compaction. The first one is nucleosomal, giving a seven-fold compaction of DNA and the composition of DNP fibrils, the second is a fibril with a diameter of 30 nm, or the nucleomeric level, with a 40-70-fold degree of packing, the third is domain-loop, or chromomeric, leading to 600-700 -fold compaction of DNA within these structures. To maintain the first two levels of compactization, the participation of only histone proteins was sufficient, while loop and rosette-like domain structures already required the participation of non-histone proteins and the transition from the helical or solenoidal type of DNA folding to the formation of compact globular structures consisting of loops of chromatin fibrils with a diameter of 30 nm , to structures of the chromomeric type, already having dimensions of 0.1-0.2 μm.

DNA packaging in chromosomes

Compactness is the fundamental difference between the eukaryotic genome and the prokaryotic genome. With an average difference in genome sizes of 3 orders of magnitude, the linear sizes of eukaryotic chromosomes are commensurate with the length of prokaryotic DNA.

There are at least 4 levels of DNA compaction. In this case, the DNA strand is "shortened" by 10,000 times. It is similar to putting a thread as long as the Ostankino Tower (500 m) into a matchbox (5 cm).

The chromosomes of eukaryotic cells consist mainly of chromatin, a complex of double-stranded DNA, and five histone proteins, designated H1, H2A, H2B, H3, and H4.

It is histones that provide the first two levels of compaction of the eukaryotic genome - nucleosomal and nucleomeric.

General characteristics of histones

Histones are the main proteins. All of them are enriched with lysine and arginine - positively charged amino acids. Depending on the ratio of amino acids in the structure of histones, 5 histone fractions are usually isolated. A lot of them are produced - 60 million molecules of each fraction per cell.

Histone modifications have a very strong effect on DNA compaction. Histones can be methylated, phosphorylated (by serine, threonine, tyrosine), i.e. amino acid residues are easily modified. In addition, alkylation and acetylation of histones is possible.

Major histone fractions:

All histones, except for H1, are extremely conserved in evolutionary terms (in cow and clover, the difference in H2A is only one amino acid!). Consequently, these proteins perform a fundamental function that is provided in the same way in all eukaryotes. Any mutation in the histone genes is lethal.

H1 is a very variable fraction. This histone is different not only in species, but even in one organism, depending on the stages of ontogeny.

In histones, lysine and arginine are clustered. The middle part of the histone contains hydrophobic amino acids. Positively charged histone amino acids provide electrostatic interactions with DNA. The central part is necessary for the interaction of histones with each other.

The role of histones in DNA folding is important for the following reasons:

1) If chromosomes were just stretched DNA, it's hard to imagine how they could replicate and separate into daughter cells without getting tangled or broken.

2) In an extended state, the DNA double helix of each human chromosome would cross the cell nucleus thousands of times; thus, histones pack a very long DNA molecule in an orderly manner into a nucleus several micrometers in diameter;

3) Not all DNA is folded in the same way, and the nature of the packaging of a region of the genome into chromatin probably affects the activity of the genes contained in this region.

Packing levels of genetic material.

First level packaging of DNA nucleosomal. The nucleosomal filament of chromatin (see above) has a diameter of about 13 nm. After packaging, the length of the DNA molecule decreases by 5-7 times. The nucleosomal level is found in electron microscope in interphase and during mitosis.

Second level packaging - solenoid(supernucleosomal). The nucleosomal strand condenses, its nucleosomes are "sewn together" by H1 histone and a helix with a diameter of about 25 nm is formed. One turn of the helix contains 6-10 nucleosomes. The thread is shortened another 6 times. The supernucleosomal level of packaging is found in the electron microscope in both interphase and mitotic chromosomes.

Third level packaging - chromatid(loop). The supernucleosomal filament coils into loops and kinks. It forms the basis of the chromatid and provides the chromatid level of packaging. It is found in prophase. The loop diameter is about 50 nm. The DNP thread is shortened by 10-20 times.

Fourth level packaging - metaphase chromosome level. Chromatids in complete spiralization: a 20-fold shortening occurs. Metaphase chromosomes are 0.2 to 150 µm in length and 0.2 to 5.0 µm in diameter. The overall result of condensation is the shortening of the DNP thread by 10,000 times!!!

Chromosomes – dense, intensely stained structures, units of the morphological organization of the genetic material and ensure its precise distribution during cell division. Chromosomes are best seen (and studied) at the metaphase stage of mitosis.

Metaphase chromosomes have the appearance of short filamentous figures, or curved rods, consisting of two longitudinal strands of DNP - chromatids. Chromatids at the inflection point ( primary constriction) are connected centromere, to which threads are attached fission spindle. The centromere divides the body of the chromosome into two arms. The area of ​​each arm near the centromere is called proximal, remote from it - distal. The terminal sections of the distal sections are called telomeres. Telomeres prevent the ends of chromosomes from joining together. The loss of these regions may be accompanied by chromosomal rearrangements. In addition to the primary constriction, individual chromosomes have secondary chromosomes that do not cause an inflection.

mosomes. The position of the secondary constriction and its length are constant for each type of chromosome. Some chromosomes also have a satellite - round or

rod-shaped body of the same nature. The satellite is connected to the main body of the chromosome by a thin chromatin thread. Sometimes a satellite is considered a part of a chromosome separated by a secondary constriction. Companion chromosomes are characteristic of plant cells.

Chromosome types. Depending on the position of the centromere, the following types of chromosomes are distinguished:

- metacentric (equilateral), the centromere is located in the middle and the arms are approximately the same length (3);

- submetacentric (unequal shoulders), the centromere is moderately displaced from the middle of the chromosome, the arms have different length (2);

- acrocentric (rod-shaped), the centromere is significantly shifted to one end of the chromosome, or located in its telomeric region, as a result, one arm is very short or absent (1).

Rice. Types of chromosomes.

The study of chromosomes made it possible to establish:

In all somatic cells of any organism, the number of chromosomes is the same;

The germ cells always contain half as many chromosomes as the somatic cells of a given type of organism;

All organisms belonging to this species, the number of chromosomes in cells is the same.

As an example, below are the diploid numbers of chromosomes in the nuclei of somatic cells of some types of organisms.

Malarial Plasmodium - 2; Horse roundworm - 2; Drosophila - 8: Head louse - 12; Spinach - 12; Housefly - 12; Perch - 28; Man - 46; Ash - 46; Chimpanzees - 48; Cockroach - 48; Pepper - 48; Sheep - 54; Dog - 78; Dove - 80; Carp - 104.

As can be seen, the number of chromosomes does not depend on the level of organization and does not always indicate a phylogenetic relationship, since the same number of chromosomes can occur in species that are very systematically distant and differ greatly in organisms close in origin. Thus, the number of chromosomes is not a species-specific trait. But, the characteristic of the chromosome set as a whole is species-specific, i.e. characteristic of only one kind of organism. The set of quantitative (number) and qualitative (shape) features of the chromosome set of a somatic cell is called karyotype .

The number of chromosomes in a karyotype is always even. This is explained by the fact that in somatic cells there are always two chromosomes of the same shape and size: one comes from the paternal organism, the other from the maternal one. Paired chromosomes that are identical in shape and size and carry the same genes are called homologous . Chromosomes from different pairs are called non-homologous . The chromosome set of a somatic cell, in which each chromosome has a pair, is called double, or diploid set(2n) . Only one of each pair of homologous chromosomes enters the germ cells, therefore the chromosome set of gametes is called single, or haploid set . The amount of DNA contained in a single set of chromosomes is 1c, respectively, in a double set the amount of DNA is 2c. Chromosomes in the karyotype are also divided into autosomes, or asexual, identical in males and females, and heterochromosomes, or sexual, involved in sex determination and differing in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (a woman has two identical X chromosomes, a man has X and Y chromosomes).

Rice. Human karyotype.

Chromosome rules.

The rule of constancy of the number of chromosomes: somatic cells of the organism of each species have a strictly defined number of chromosomes (in humans - 46, in Drosophila - 8).

Chromosome pairing rule: each chromosome in the diploid set has a homologous one - similar in size, centromere location and gene content.

Chromosome Individuality Rule: each pair of chromosomes differs from the other pair in size, centromere location and gene content.

Chromosome continuity rule: in the process of doubling the genetic material, a new DNA molecule is synthesized based on the information of the old DNA molecule (the reaction of matrix synthesis - each chromosome from a chromosome).

Table 1

Comparative characteristics prokaryotic and eukaryotic cells

PROKARYOTIC CELL	EUKARYOTIC CELL
cytoplasmic membrane	cytoplasmic membrane
Murein cell wall	Cellulose wall (plants) or chitin (fungi)
Cytoplasm	Cytoplasm
No formalized core	The nucleus separated from the cytoplasm by the nuclear membrane
There are no organelles: mitochondria, Golgi complex, EPS, lysosomes, plastids	There are mitochondria, the Golgi complex, EPS, lysosomes, plastids.
Mesosomes perform the functions of a number of organelles.	Mesosomes are absent
Ribosomes	Ribosomes
The genetic apparatus is represented by a single circular DNA molecule	Linear DNA in complex with histone proteins
The set of chromosomes is haploid	The set of chromosomes is diploid, or haploid in some phases of life.
Simple binary division	Mitosis, meiosis, amitosis, endomitosis, polythenia.

Table 2.

Comparative characteristics of plant and animal cells

Keywords and concepts :

active transport

golgi apparatus

autosomes

biological membrane

Inclusions

Haploid set of chromosomes

Heterochromosomes

homologous chromosomes

Diploid set of chromosomes

Diffusion

Karyoplasm

Karyotype

Leucoplasts

microtubules

Microfilaments

Mitochondria

Non-homologous chromosomes

Organelles

Passive transport

pinocytosis

proplastida

Cilia

Ribosome

Thylakoid

Phagocytosis

Chloroplast

Chromatin

Chromoplast

Chromosome

Centriole

Centrosome

cytoplasmic membrane

Exocytosis

Endoplasmic reticulum agranular

Endoplasmic reticulum granular

DNA molecules in eukaryotic cells are very large. Thus, the length of DNA molecules isolated from human cells reaches several centimeters. It is generally accepted that each eukaryotic chromosome contains one - the only continuous DNA molecule. Taking into account the species number of chromosomes in mammals, we can say that, on average, they have about 2 m of DNA per interphase nucleus, which is located in a spherical nucleus with a diameter of less than 10 μm. At the same time, a certain order of arrangement of DNA molecules must be preserved in the nucleus in order to ensure its ordered functioning.

DNA molecules in the nuclei of eukaryotic cells are always in complex with proteins in the composition of chromatin, which is formed from chromosomes after the end of nuclear division as a result of a complex process of unwinding (despiralization) of chromosomes.

Proteins account for about 60% of the dry weight of chromatin. The proteins in its composition are very diverse. They are usually divided into two groups: histones and non-histone proteins. It is histones, characteristic only for eukaryotic cells, that carry out the first stages of DNA packaging, which are very similar in most of the studied objects.

Histones account for up to 80% of all chromatin proteins. Their interaction with DNA occurs due to ionic bonds and does not depend on the sequence of nucleotides in the DNA molecule. Histones are not very diverse. These are globular proteins represented by 5-7 types of molecules. The best known classes of histones are HI, H2A, H2B, H3, and H4. Their basic properties determined relative to high content basic amino acids: lysine and arginine (Fig. 3.7). Positive charges on the amino groups of these amino acids provide an electrostatic bond between histones and negative charges on the phosphate groups of DNA. Of all the nuclear proteins, histones are the best studied. Their molecular weight is relatively small (the maximum is for the H3 histone - 153 thousand daltons). In almost all eukaryotes, they have similar properties and are divided into the same classes. Of the studied proteins, these proteins are the most conservative: their amino acid sequences are similar even in distant species. The exception is HI histones, which are characterized by significant interspecies and intertissue variations.

During the life of cells, histones can undergo post-translational modifications, which change their properties and ability to bind to DNA. Histones are synthesized in the cytoplasm, transported to the nucleus, and bind to DNA during its replication in the S-period of the cell cycle. Histones incorporated into chromatin are very stable and have low speed exchange.

The presence of histones in all eukaryotic cells, their similarity even in very distant species, their obligatoriness in the composition of chromosomes and chromatin - all this indicates the extremely important role of these proteins in the life of cells. A landmark event in the study of DNA packaging in chromatin was the discovery of particle nucleosomes, in which the first stage of DNA packaging in chromatin occurs. The core of the nucleosome is always conservative, contains eight molecules: two molecules of histones H4, H3, H2A, H2B each. On the surface of the core is a DNA segment of 146 nucleotide pairs, forming 1.75 turns around the core. A small section of DNA remains unbound to the core, it is called a linker (Fig. 3.8). In different objects, the linker site can vary from 8 to 114 nucleotide pairs per nucleosome.

It is calculated that the entire haploid human genome (3 x 109 base pairs) accounts for 1.5 x 107 nucleosomes. General form chromatin, represented by a DNA molecule packaged using nucleosomal structures, can be compared to beads on a string (Fig. 3.9). Nucleosomes are capable of self-assembly in the presence of DNA and histones in a test tube in a certain ratio. The first nucleosomal level of DNA compaction increases the packing density of DNA by 6-7 times.

The nucleosomal structure of chromatin is involved in the next stage of packaging with the help of histone HI, which binds to the linker portion of DNA and the surface of the nucleosome. Due to the complex interaction of all components, an ordered structure of a spiral type arises, which is often called a solenoid (Fig. 3.10). It increases the compactness of DNA by another 40 times. Because the solenoid structure has a reduced ability to bind to proteins that mediate transcription, it is believed that this level of DNA compaction may act as a gene-inactivating factor. Some authors consider the solenoid structure as one of the options chromatin packaging

with the help of histone HI and consider the existence of other morphological variants, for example, the nucleomer, or superbeads, to be probable (Fig. 3.11).

More high levels DNA compaction in chromatin is associated with non-histone proteins. They account for about 20% of all chromatin proteins. This assembled group of proteins is distinguished by a wide range of properties and functions. In total, the fraction of non-histone proteins combines about 450 individual proteins, the properties and specific functions of which have not yet been sufficiently studied. It was found that some of them specifically bind to certain DNA regions, as a result of which chromatin fibrils form loops at the sites of DNA binding to non-histone proteins. Thus, higher levels of DNA packaging in chromatin are provided not by spiralization of chromatin threads, but by the formation of a transverse looped structure along the chromosome (Fig. 3.12). At all these stages of DNA compaction, chromatin is present in an active form; transcription and synthesis of all types of RNA molecules take place in it. Such chromatin is called euchromatin. Further packaging of chromatin leads to its transition to an inactive state with the formation of heterochromatin.

This process is associated with the spiralization of loop groups and the formation of rosette-like structures from chromatin fibrils, which have optical and electron density and are called chromomeres (Fig. 3.12). It is assumed that along the chromosome is located a large number of chromomeres interconnected into a single structure by sections of chromatin with pucleosomal or solenoidal DNA packaging. Each pair of homologous chromosomes has its own chromomeric pattern, which can be detected using special staining methods, provided that the chromatin is siaralized and transferred to the chromosome state.

The loop-rosette structure of chromatin provides not only DNA packaging, but also organizes functional chromosomes, since at their bases DNA loops are associated with non-histone proteins, which may include replication enzymes that provide DNA duplication, and transcription enzymes, due to which all types of synthesis occur. RNA.

DNA regions packaged in the form of heterochromatin can have a dual nature. There are two types of heterochromatin: facultative and constitutive (structural). Facultative heterochromatin is a part of the genome that is temporarily inactivated in certain cells. An example of such chromatin is the sex heterochromatin of the inactivated X chromosome in somatic cells of women. Structural heterochromatin in all cells is constantly in an inactive state and probably performs structural or regulatory functions.

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1) Nucleosomal - at this level, the DNA double helix is ​​wound around a protein complex containing 8 histone molecules - proteins with an increased content of positively charged amino acid residues of lysine and arginine. These are the histones H2B, H2A, H4 and H3. A structure with a diameter of 11 nm is formed, resembling beads on a string. Each "bead" - the nucleosome contains about 150 base pairs. The nucleosomal level gives a shortening of the DNA molecule by 7 times. During replication, this level of packaging is removed, while during transcription, nucleosomes are preserved.

2) At the second level, nucleosomes approach each other with the help of histone H1, resulting in the formation of a fibril with a diameter of 30 nm. The reduction in the linear size of DNA occurs by 6-10 times. This level of packaging, like the first one, does not depend on the primary structure of DNA.

3) Loop level. Provided by non-histone proteins. They recognize certain DNA sequences and bind to them and to each other, forming loops of 20-80 thousand bp. Shortening due to loops takes place 20-30 times. A typical mammalian chromosome can contain up to 250 loops.

4) metaphase chromosome. Before cell division, DNA molecules are doubled, the loops are stacked, the chromosome thickens and is visible under a light microscope. At this packing level, each chromosome consists of two chromatids. Each chromatid contains one DNA molecule.

Functions of DNA.

1. DNA is the carrier of genetic information. The function is provided by the fact of existence genetic code.

2. Reproduction and transmission of genetic information in generations of cells and organisms. The function is provided by the process replication .

3. Implementation of genetic information in the form of proteins, as well as any other compounds formed with the help of enzyme proteins. Function provided by processes transcriptions and broadcasts .

Directly from the structure of DNA follows the mechanism of its exact reproduction (replication). DNA structure replication is based on the principle complementarity : in a double helix, two DNA polymer chains are connected to each other due to the formation of pairs G - C, C - G, A - T, T - A. If two chains of the double helix diverge, then a new complementary chain can be built on each of them - opposite G of the original chain, the C of the new chain will be established, opposite the C of the old chain - G of the new chain, opposite A - T, and opposite T - A. As a result, two child double helixes will be obtained, completely identical to the original - parent.

Ribonucleic acids ubiquitous in nature. biological function RNA is due to the fact that they ensure the implementation in the cell of hereditary information that is transmitted using DNA.

There are three main types of RNA in the cell: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).

RNA is a polynucleotide similar to DNA, but with its own characteristics.

1) The carbohydrate in RNA is represented by ribose, which has a hydroxyl group in the second position of the carbon atom.

2) Unlike DNA, the molecules of all three types of RNA are single-stranded, which is one of the important features of RNA. Moreover, distinctive feature RNA is that it is not characterized by a stable helical structure.

3) RNA contains 4 nitrogenous bases - adenine, cytosine, guanine and uracil.

The following general principles of the structure of all types of RNA are distinguished:

1) RNA is a single-stranded polynucleotide.

2) RNA forms a secondary structure - a set of short helical sections, which are formed due to antiparallel complementary pairing of adjacent segments of the chain.

3) RNA is able to form a tertiary structure due to long-range complementary interactions within the strand and interstrand interactions.

4) High polymeric RNA is able to fold into compact particles.

5) RNA has significant conformational mobility.