DNA nucleotide consists of. Deoxyribonucleic acid (DNA). Implementation of hereditary information
After the opening of the principle of molecular organization of such a substance as DNA in 1953, began to develop molecular biology. Further, in the process of research, scientists found out how the DNA is recombined, its composition and how our human genome is arranged.
Every day the molecular level occurs the most complex processes. How is the DNA molecule, what is it from? And what role is played in the cell of the DNA molecule? We will describe in detail about all the processes occurring inside the double chain.
What is hereditary information?
So why did it all start? Another 1868 found bacteria in nuclei. And in 1928, N. Koltsov highlighted the theory that all genetic information about living organism was encrypted into DNA. Then J. Watson and F. Creek found a model now the well-known DNA spiral in 1953, for which the recognition and award was deserved - the Nobel Prize.
What is DNA in general? This substance consists of 2 combined threads, or rather spirals. The plot of such a chain with certain information is called the genome.
The DNA stores all the information about the fact that proteins will be formed and in what order. DNA macromolecule is a material carrier of incredibly volumetric information that is recorded by a strict sequence of individual bricks - nucleotides. Total nucleotides 4, they complement each other chemically and geometrically. This principle of addition, or complementarity, will be described later in science later. This rule plays a key role in encoding and decoding genetic information.
Since the DNA thread is incredibly long, the repetitions in this sequence does not happen. Each living creature has its own unique DNA chain.
DNA functions
The functions include storing hereditary information and its transfer to the offspring. Without this function, the genome of the species could not be maintained and developed for thousands of years. Organisms that have undergone serious gene mutations, do not more often survive or lose the ability to produce offspring. So there is natural protection against the degeneration of the species.
Another essential function is the implementation of stored information. The cell cannot create any vital protein without those instructions that are stored in a double chain.
Composition of nucleic acids
Now it is already reliably known, from which the nucleotides themselves are - DNA bricks. Their composition includes 3 substances:
- Orthophosphoric acid.
- Nitrogen base. Pyrimidine bases - which have only one ring. These include Timin and Cytosin. Purine bases, which contain 2 rings. This is Guanine and Adenin.
- Sucrose. As part of DNA - deoxyribosis, in RNA - robose.
The number of nucleotides is always equal to the number of nitrogenous bases. In special laboratories, nucleotides are cleaved and a nitrogenous base is distinguished from it. This is how the individual properties of these nucleotides and possible mutations in them are studied.
Levels of the organization of hereditary information
Separate 3 levels of organization: gene, chromosomal and genomic. All information needed for the synthesis of a new protein is contained on a small segment of the chain - gene. That is, the gene is considered the lowest and the easiest level of encoding information.
Genes, in turn, are collected in chromosomes. Thanks to such an organization of the hereditary material of a group of signs according to certain laws, alternate and transmitted from one generation to another. It should be noted, the genes in the body are incredibly much, but the information is not lost, even when it is recombaling many times.
Several types of genes are separated:
- according to the functional purpose, 2 types are isolated: structural and regulatory sequences;
- by influence on the processes occurring in the cell, they distinguish: supervital, lethal, conditionally lethal genes, as well as genes Mutators and antimutators.
There are genes along the chromosome in linear order. In chromosomes, the information is focused not by the rules, there is a certain order. There is even a map in which the positions or locuses of gene are displayed. For example, it is known that in chromosome No. 18, data about the color of the child's eye is encrypted.
What is the genome? This is so called the entire set of nucleotide sequences in the body's cell. The genome characterizes whole view, not a separate individual.
What is the human genetic code?
The fact is that the whole of the most huge potential of human development has already been laid during the conception. All hereditary information, which is necessary for the development of the zygota and the growth of the child after birth, is encrypted in genes. DNA sections are the most basic carriers of hereditary information.
Human 46 chromosomes, or 22 somatic couples plus one-defining chromosome floor from each parent. This diploid chromosome set encodes the entire physical appearance of a person, his mental and physical abilities and predisposition to diseases. Somatic chromosomes externally indistinguishable, but they carry different information, as one of them from the Father, the other is from the mother.
Male code differs from the female latter couple chromosomes - Hu. The female diploid set is the last couple, XX. Men get one x-chromosome from a biological mother, and then it is transmitted to daughters. The sexual y-chromosome is transmitted to sons.
The human chromosomes differ significantly in size. For example, the smallest pair of chromosomes - №17. And the largest steam is 1 and 3.
Diameter double spiral The person has 2 nm. DNA is so tightly twisted that it contains in the small core of the cell, although its length will reach 2 meters, if you promote it. The length of the spiral is hundreds of millions of nucleotides.
How is the genetic code transmitted?
So, what role do DNA molecule play in the cell? Genes are carriers of hereditary information - are located inside each cell cell. To transfer your code a child organism, many creatures share their DNA on 2 identical spirals. This is called replication. In the DNA replication process, special "machines" complement each chain. After the genetic spiral is repaid, it begins to divide the core and all organelles, and then the whole cell.
But a person has another process of gene transfer - sexual. Signs of father and mothers are mixed, in the new genetic code contains information from both parents.
Storage and transfer of hereditary information are possible thanks to the complex organization of the DNA spiral. After all, as we said, the structure of proteins is encrypted in genes. When creating during conception, this code throughout his life will copy itself. Kariotype (personal set of chromosomes) does not change during the update of organ cells. The transmission of information is carried out with the help of genital heams - male and female.
Only viruses containing one RNA chain are not capable of transmitting its information. Therefore, to reproduce, they need human or animal cells.
Implementation of hereditary information
In the kernel, the cells are constantly important processes. All information recorded in chromosomes is used to build proteins from amino acids. But the DNA chain never leaves the kernel, so I need to help another an important compound \u003d RNA. RNA is able to penetrate the kernel membrane and interact with the DNA chain.
Through the interaction of DNA and 3 types of RNA, all encoded information is implemented. At what level is the implementation of hereditary information? All interactions occur at the level of nucleotides. Information RNA copies the DNA chain portion and brings this copy to Ribosoma. Here begins the synthesis of the nucleotide of the new molecule.
In order for the IRNK to copy the necessary part of the chain, the spiral unfolds, and then, upon completion of the transcoding process, is restored again. Moreover, this process can occur simultaneously on 2 sides of 1 chromosome.
Principle of complementarity
Consist of 4 nucleotides are adenine (a), guanine (G), cytosine (C), Timin (T). They are connected by hydrogen bonds according to the rule of complementarity. E. Chargaff's work helped to establish this rule, since the scientist noticed some patterns in the behavior of these substances. E. Chargaff discovered that adenine molar ratio to thimin is equal to one. And just as the ratio of guanin to the cytosine is always equal to one.
Based on its works, genetics have formed a rule of interaction between nucleotides. The complementarity rule states that adenine is connected only with thimine, and a guanine with a cytosine. During decoding the spiral and synthesis of the new protein in the ribosome, such an alternation rule helps to quickly find the necessary amino acid, which is attached to the transport RNA.
RNA and its types
What is hereditary information? Nucleotides in DNA double chain. What is RNA? What is her job? RNA, or ribonucleic acid helps to extract information from DNA, decode it and based on the principle of complementarity to create the necessary protein cells.
Total distinguished 3 types of RNA. Each of them performs strictly its function.
- Information (IRNA), or it is also called a matrix. She comes right in the center of the cage, in the core. Finds in one of the chromosomes the necessary genetic material for the protein construction and copies one of the sides of the double chain. Copy occurs again on the principle of complementarity.
- Transport - This is a small molecule, which on one side of the nucleotide decoders, and on the other side the corresponding amino acid codes. The task of TRNA is to deliver to the "shop", that is, in Ribosoma, where the necessary amino acid synthesizes.
- rRNA - Ribosomal. It controls the amount of protein that is produced. Consists of 2 parts - an amino acid and peptide plot.
The only difference during decoding is no thymine on RNA. Instead of Timine there is a Uracil. But then, in the process of protein synthesis, all the amino acids are still correctly installed when TRNA. If some faults occur in decoding information, mutation arises.
Reparation of the damaged DNA molecule
The recovery process of the damaged double chain is called repair. In the process of repairing damaged genes are removed.
Then the required sequence of elements is exactly played and cut back to the same place on the chain, from where it was extracted. All this is due to special chemicals - Enzymes.
Why do mutations occur?
Why do some genes begin to mutate and cease to perform their function - storing the vital hereditary information? This is due to an error during decoding. For example, if adenine is accidentally replaced by Timin.
There are also chromosomal and genomic mutations. Chromosomal mutations happen if the sections of hereditary information fall out, doubles either generally transferred and embedded in another chromosome.
Genomic mutations are most serious. Their cause is a change in the number of chromosomes. That is, when instead of a pair - the diploid set is present in the karyotype triploid set.
The most famous example of triploid mutation is a Down syndrome, in which a personal set of chromosomes 47. These children formed 3 chromosomes on the site of the 21st pair.
Also known is such a mutation as polymploy. But polymploy is found only in plants.
Nucleic acids are high molecular weight substances consisting of mononucleotides, which are connected to each other into a polymer chain using 3 ", 5" - phosphodieter bonds and packed in cells in a certain way.
Nucleic acids - biopolymers of two varieties: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Each biopolymer consists of nucleotides, differing in carbohydrate residue (ribose, deoxyribose) and one of nitrogen bases (Uracil, Timin). Accordingly, these differences are nucleic acids and obtained their name.
The structure of deoxyribonucleic acid
Nucleic acids have a primary, secondary and tertiary structure.
Primary DNA structure
The primary structure of DNA is called a linear polynucleotide chain, in which mononucleotides are connected to 3 ", 5" -phosphodieter connections. The source material in the assembly of the nucleic acid circuit in the cell is nucleoside 5 "-tritosphate, which, as a result of the removal of β and γ, phosphoric acid residues can attach 3" -At carbon of another nucleoside. Thus, 3 "carbon of one deoxyribose carbon is covalently binds to the 5" carbon of other deoxyribose, by means of one residue of phosphoric acid and forms a linear polynucleotide chain of nucleic acid. Hence the name: 3 ", 5" -phosphodieter ties. Nitrogen bases do not participate in the connection of the nucleotide of one chain (Fig. 1.).
Such a compound, between the residue of the phosphoric acid molecule of one nucleotide and the carbohydrate of the other, leads to the formation of a pentoso phosphate skeleton of a polynucleotide molecule, at which one after the other is joined by nitrogen bases. Their sequence of location in chains of nucleic acid molecules is strictly specific for cells of different organisms, i.e. Wears species character (chargaff rule).
The DNA linear chain, the length of which depends on the number of nucleotide-in-circuits, has two end: one is called 3 "-concons and contains free hydroxyl, and the other - 5" -concons, contains the residue of phosphoric acid. The polarna chain and may have an injection 5 "-\u003e 3" and 3 "-\u003e 5". The exceptions are ring DNA.
The genetic "text" of DNA is compiled using code "words" - tripts of nucleotides, called codons. DNA sections containing information about the primary structure of all types of RNA are called structural genes.
Polynucleic DNA chains reach gigantic sizes, so they are packed in a certain way in the cell.
Studying the DNA composition, Charguff (1949) established important patterns regarding the content of separate DNA bases. They helped to reveal the secondary DNA structure. These patterns are called the rules of Chargaff. Chargaff rules
These rules suggest that when constructing DNA, a rather strict compliance (mating) of non-purin and pyrimidine bases should be observed in general, and specifically thymine with adenine and cytosine with guanin. Based on these rules, among other things, in 1953, Watson and Creek proposed the model of the secondary DNA structure, the name of the double helix (Fig.). |
Secondary DNA structure
The secondary structure of DNA is a double spiral, the model of which was proposed by D.Uoton and F. Krikom in 1953.
Prerequisites for the creation of a DNA model
As a result of initial analyzes, there was an idea that DNA of any origin contains all four nucleotides in equal molar quantities. However, in the 1940s, E. Chargaff and his staff as a result of the analysis of DNA isolated from a variety of organisms, clearly showed that nitrogenous bases are contained in their various quantitative relations. Chargaff found that, although these relations are the same for DNA from all cells of the same type of organisms, DNA from different types may noticeably differ in the content of certain nucleotides. It suggested that the differences in the ratio of nitrogen bases may be associated with some biological code. Although the ratio of individual purine and pyrimidine bases in various DNA samples turned out to be unequal, when comparing, a certain pattern was revealed, in all samples, the total number of purines was equal to the total number of pyrimidines (A + G \u003d T + C), the amount of adenine - the amount of thymine (and \u003d T), and the amount of guanin is the amount of cytosine (r \u003d c). DNA isolated from mammalian cells was generally richer adenine and thime and relatively poor guanin and cytosin, while DNA bacteria had a richer guanine and cytosine and relatively poor adenine and thime. These data amounted to an important part of the actual material, on the basis of which the model of the structure of Watson's DNA structure was later constructed - a scream.
Another important indirect indication of the possible structure of DNA was the data of L. Polingong on the structure of protein molecules. Polneg showed that several different stable configurations of the amino acid circuit in the protein molecule are possible. One of the common configurations of the peptide chain is an α-helix - is the correct screw-like structure. With such a structure, the formation of hydrogen bonds between amino acids located on the adjacent turns of the chain is possible. Polneg described the α-spiral configuration of the polypeptide chain in 1950 and suggested that the DNA molecules probably have a spiral structure fixed with hydrogen bonds.
However, the most valuable information on the structure of the DNA molecule was given the results of x-ray structural analysis. X-rays, passing through the DNA crystal, undergo diffraction, i.e., deviate in certain directions. The degree and nature of the radiation deviation depend on the structure of the molecules themselves. The diffraction radiograph (Fig. 3) gives an experiencing a number of indirect indications regarding the structure of the molecules of the studied substance. The analysis of DNA diffraction radiographs led to the conclusion that nitrogenous bases (having flat shape) Look like a stack of plates. Radiographs made it possible to reveal three main periods in the structure of crystalline DNA: 0.34, 2 and 3.4 nm.
Watson Creek DNA Model
Based on the analytical data of Chargaff, the radiographs obtained by Wilkins and the studies of chemists, providing information on the exact distances between atoms in the molecule, about the corners between the bonds of this atom and the value of atoms, Watson and the cry began to build the physical models of the individual components of the DNA molecule at a certain scale and "customized" to each other with such a calculation so that the obtained system corresponds to various experimental data [show] .
Even earlier, it was known that in the DNA chain, the neighboring nucleotides are connected by phosphodieter bridges, binding 5 "-carbon atom of deoxyribose of one nucleotide with a 3-carbon deoxyribose atom of the next nucleotide. Watson and Creek did not doubt that a period of 0.34 nm corresponds to the distance between sequential nucleotides in the DNA chain. Next, it was possible to assume that a period of 2 nm corresponds to the thickness of the chain. And in order to explain what real structure corresponds to a period of 3.4 nm, Watson and Creek, as early as Paulong, suggested that the chain is twisted in the form of a spiral (or, more precisely, forms a screw line, as the spiral in the strict sense of this Words turns out when the turns form a conical, and non-cylindrical surface in the space). Then the period of 3.4 nm will correspond to the distance between the consecutive turns of this helix. Such a helix can be very dense or somewhat stretched, i.e., it can be gentle or steep. Since a period of 3.4 nm is exactly 10 times the distance between sequential nucleotides (0.34 nm), it is clear that each spiral forces contains 10 nucleotides. According to these data, Watson and Creek were able to calculate the density of the polynucleotide chain, twisted into a spiral with a diameter of 2 nm, with a distance between the coils equal to 3.4 nm. It turned out that such a chain density would be twice as much as the actual DNA density, which was already known. It was necessary to assume that the DNA molecule consists of two chains - that this is a double spiral from nucleotides.
The next task was, of course, finding out the spatial relationship between both chains forming a double helix. Having tried on its physical model, a number of chain layout options, Watson and Cryp found that all available data corresponds to such a variant in which two polynucleotide spirals go in opposite directions; At the same time, the chains consisting of sugar and phosphate residues form the surface of the double helix, and purines and pyrimidines are located inside. The bases belonging to each other belonging to two chains are pairly connected by hydrogen bonds; It is these hydrogen bonds that hold the chains together by locking the overall configuration of the molecule.
DNA double helix can be imagined in the form of a screw-like twisted rope ladder so that the crossbars remain in a horizontal position. Then two longitudinal ropes will correspond to chains from sugar and phosphate residues, and crossbars - nitrogenous base pairs connected by hydrogen bonds.
As a result of further study of possible models, Watson and Creek came to the conclusion that each "crossbar" should consist of one purine and one pyrimidine; With a period of 2 nm (which corresponds to the diameter of the double helix), there would not be enough space for two Purines, and two pyrimidine could not be located close enough to each other to form proper hydrogen bonds. An in-depth study of a detailed model has shown that adenine and cytosine, making up a combination suitable in size, still could not be located in such a way that hydrogen bonds are formed between them. Similar reports forced to exclude also a combination of Guanin - Timin, whereas the combinations of adenine - Timin and Guanin - cytosin turned out to be quite acceptable. The nature of hydrogen bonds is such that adenine forms a pair with thymin, and guanine - with a cytosine. This idea of \u200b\u200ba specific mating of foundations allowed to explain the "Chargaff rule", according to which the amount of adenine is always equal to the content of thymine, and the amount of guanin is the amount of cytosine. Two hydrogen bonds are formed between adenine and thimin, and there are three between the guanin and cytosine. Due to this specificity in the formation of hydrogen bonds against each adenine in one chain, Timin turns out to be in another; In the same way, only cytosine can be against each guanin. Thus, the chains are complementary to each other, i.e., the sequence of nucleotides in one chain uniquely determines their sequence in another. Two chains go in opposite directions, and their end phosphate groups are at opposite ends of the double helix.
As a result of his research, in 1953, Watson and Creek proposed the structure of the structure of the DNA molecule (Fig. 3), which remains relevant to the present. According to the model, the DNA molecule consists of two complementary polynucleotide chains. Each DNA circuit is a polynucleotide consisting of several tens of thousands of nucleotides. In it, the adjacent nucleotides form a regular pentoso phosphate cable due to the compound of the residue of phosphoric acid and deoxyribose durable covalent tie. The nitrogen bases of one polynucleotide chain are arranged in a strictly defined order against nitrogenous bases of the other. The alternation of nitrogenous bases in the polynucleotide chain is irregular.
The location of nitrogen bases in the DNA circuit is complementary (from the Greek. "Complement" is an add-on), i.e. Adenin (a) is always Timin (T), and against guanin (g) is only cytosine (C). This is explained by the fact that a and t, as well as r and c strictly correspond to each other, i.e. complement each other. Such a correspondence is given by the chemical structure of the base, which allows for the formation of hydrogen bonds in a pair of purine and pyrimidine. There are two bonds between A and T, between G and C - three. These bonds provide partial stabilization of the DNA molecule in space. The stability of the double helix is \u200b\u200bdirectly proportional to the number of G≡S bonds, which are more stable compared with the connections A \u003d t.
The known sequence of nucleotide location in one DNA circuit allows for the principle of complementarity to establish nucleotides of another chain.
In addition, it was established that nitrogenous bases having an aromatic structure in aqueous solution are located one over the other, forming a stack of coins. Such a process of forming a pile from organic Molecules called stingy. The polynucleotide chains of the DNA molecule under consideration of the Watson-Creek model have a similar physicochemical state, their nitrogenous bases are located in the form of a stack of coins, between the planes of which there are van der Wales interaction (stroke-interactions).
Hydrogen bonds between complementary bases (horizontally) and glass interaction between the base planes in the polynucleotide chain due to Van der Wales forces (vertically) provides a DNA molecule to additional stabilization in space.
Sakharoophosphate cozers of both chains are turned outward, and the bases inside, towards each other. The direction of the chains in the DNA antipherallylno (one of them has a direction 5 "-\u003e 3", the other - 3 "-\u003e 5", i.e. 3 "Conclusion of one chain is located opposite 5" -Conny another.). The chains form right spirals with a common axis. One spiral turn is 10 nucleotides, the size of the cooler is 3.4 nm, the height of each nucleotide is 0.34 nm, the diameter of the helix is \u200b\u200b2.0 nm. As a result of the rotation of the same circuit around the other, a large groove is formed (with a diameter of about 20 Å) and a small furrow (about 12 Å) DNA double helix. Such a shape of the double spiral of Watson-Cry was in the future received the name of the B-forms. In DNA cells, usually exists in in-form, which is the most stable.
DNA functions
The proposed model explained many biological properties of deoxyribonucleic acid, including the storage of genetic information and the manifold of genes, provided by a large variety of consecutive combinations of 4 nucleotides and the fact of existence genetic code, the ability to reproduce and transfer genetic information provided by the replication process and the implementation of genetic information in the form of proteins, as well as any other compounds formed by protein-enzymes.
Optional DNA functions.
- DNA is a carrier of genetic information, which is ensured by the fact of the existence of a genetic code.
- Reproduction and transferred genetic information to generations of cells and organisms. This feature is provided by the replication process.
- The implementation of genetic information in the form of proteins, as well as any other compounds generated by protein-enzymes. This feature is provided by transcription and broadcast processes.
Forms of the organization of double-stranded DNA
DNA can form several types of double helix (Fig. 4). Currently, six forms are already known (from A to E and Z-form).
The structural forms of DNA, as the Franklin rosalynd installed, depend on the saturation of the nucleic acid molecule. In studies, DNA fibers using X-ray structural analysis, it was shown that the radiograph radically depends on that with what relative humidity, with what extent saturation of this fiber is experiment. If the fiber was sufficiently saturated with water, then one radiograph was obtained. When drying, a completely different X-ray diffraction pattern arose, highly different from high humidity radiographs.
High humidity DNA molecule received name in-form. Under physiological conditions (low salt concentration, high gear of hydration), the dominant structural type of DNA is in-form (the main form of two-stranded DNA is the Watson Creek model). Spiral pitch of such a molecule is 3.4 nm. There are 10 complementary pairs in the form of twisted stacks "coins" - nitrogenous bases. Stacks are held with hydrogen bonds between the two opposite "coins" of the pile, and "wrapped" with two tapes of the phosphodieter island swirling into the right spiral. The planes of nitrogen bases are perpendicular to the axis of the spiral. Neighboring complementary pairs are rotated relative to each other by 36 °. The diameter of the helix 20Å, and the purin nucleotide takes 12Å, and pyrimidine - 8Å.
DNA Molecule Low Humidity Receives Name A-forms. A-form is formed in less than high hydration and at a higher content of Na + or K + ions. This wider right-wing conformation has 11 pairs of nitrogenous bases for the turn. The planes of nitrogen bases have a stronger slope to the spiral axis, they are rejected from normal to the spiral axis by 20 °. It follows the presence of an internal emptiness with a diameter of 5Å. The distance between adjacent nucleotides is 0.23 nm, the length of the turn is 2.5 nm, the diameter of the spiral is 2.3 nm.
It was originally believed that the A-form DNA is less important. However, in the future, it turned out that the A-form of DNA, as well as in-form, has a huge biological significance. The A-form has a RNA-DNA helix in the seed matrix complex, as well as the RNA-RNA spiral and RNA spiker structures (2'-hydroxyl group of ribose does not allow RNA molecules to form a form). A-form DNA is found in disputes. It has been established that the DNA A-form is 10 times more stable to the action of UV rays than the form.
A-shape and the form is called canonical DNA forms.
Shapes sch Also, the rustic, their education can be observed only in special experiments, and, apparently, they do not exist in vivo. The C-form of DNA has a structure similar to B-DNA. The number of pairs of reasons for the coil is 9.33, the length of the spiral spiral is 3.1 nm. The base pairs are tilted at an angle of 8 degrees relative to perpendicular position to the axis. The grooves are close to in-DNA grooves. At the same time, the main groove is slightly smaller, and minor grooves are deeper. Natural and synthetic DNA polynucleotides can be moved to C-form.
| Table 1. Characteristics of some types of DNA structures | |||
| Type of Spiral | A. | B. | Z. |
| Pag Spiral | 0.32 Nm | 3.38 Nm | 4.46 nm |
| Spiral twisted | Right | Right | Left |
| Number of pair of reasons | 11 | 10 | 12 |
| Distance between base planes | 0.256 Nm | 0.338 nm | 0.371 Nm |
| Conformation of glycosidic communication | anti | anti | anti-S. sIN-G. |
| Conformation of furanous cycle | C3 "-Endo | C2 "-Endo | C3 "-Endo-g C2 "-Endo-c |
| The width of the groove, small / big | 1,11 / 0.22 nm | 0.57/117 nm | 0.2 / 0.88 nm |
| The depth of grooves, small / large | 0.26 / 1.30 nm | 0.82 / 0.85 nm | 1.38 / 0.37 nm |
| Diameter Spiral | 2.3 nm | 2.0 Nm | 1.8 nm |
Structural elements of DNA
(non-canonical DNA structures)
The structural elements of DNA include unusual structures limited by some special sequences:
|
Z-form DNA It was discovered in 1979 when studying hexanucleotide D (CG) 3 -. It was opened by Professor Massachusetts Institute of Technology Alexander Rich with employees. Z-form has become one of the most important structural elements DNA due to the fact that its formation was observed in the DNA sections, where purries alternate with pyrimidians (for example, 5'-HGGCH-3 '), or in the repetitions of 5'-CGCGG-3' containing methylated cytosin. An essential condition for the formation and stabilization of Z-DNA was the presence of purine nucleotides in X-conformation, alternating with pyrimidine bases in anti-conformation.
Natural DNA molecules mostly exist in the right B form if they do not contain type (CG) n sequences. However, if such sequences are part of DNA, then these areas with a change in the ionic force of the solution or cations neutralizing negative charge On the phosphodieter frame, they can go to the Z-form, while other DNA sections in the chain remain in classical in-form. The possibility of such a transition indicates that the two chains in the DNA double helix are in a dynamic condition and can be unwound relative to each other, moving from the right form to the left and vice versa. The biological consequences of such lability allowing the conformational transformations of the DNA structure is not quite understandable yet. It is believed that the Z-DNA sites play a certain role in regulating the expression of some genes and take part in genetic recombination.
The Z-shape of DNA is a left-handed double helix in which the phosphodieter base is located zigzago-like along the axis of the molecule. Hence the name of the molecule (zigzag) -dhk. Z-DNA - the least twisted (12 pairs of reasons for the cooler) and the most subtle of nature known in nature. The distance between adjacent nucleotides is 0.38 nm, the length of the turn is 4.56 nm, the diameter of Z-DNA is 1.8 nm. Moreover, appearance This DNA molecule is distinguished by the presence of one groove.
The DNA z-form was detected in prokaryotic cells and eukaryotes. Currently, antibodies are obtained that can distinguish the Z-form from the B-forms of DNA. These antibodies are associated with certain areas of the giant chromosomes of the cells of the salivary glands of the Drozophila (Dr. Melanogaster). Behind the binding response is easy to monitor due to the unusual structure of these chromosomes, which have more dense areas (discs) contrast with less dense (interdisciplies). Z-DNA sites are located in interdisciplons. It follows from this that the Z-form really exists in vivo, although the dimensions of individual sections of Z-form are still unknown.
(Perevils) - the most famous and frequent foundations in the DNA. Palindrome is called the word or phrase, which is read from left to right and vice versa is the same. Examples of such words or phrases are: Shalash, Cossack, Flood, and Rosa fell on the Lap of Azor. In applied to DNA sites, this term (palindrome) means the same alternation of nucleotides along the chain to the right left and from left to right (like letters in the word "shala", etc.).
Palindrome is characterized by the presence of inverted repetition of the base sequences having a second-order symmetry relative to two DNA circuits. Such sequences, by a completely understandable reason, are self-checking and tend to the formation of studded or cruciform structures (Fig.). Studs help regulators to learn the place of chromosome genetic text chromosomes.
In cases where the inverted repetition is present in the same DNA chain, such a sequence is called a mirror repeat. Mirrored repetitions do not have the properties of self-checking and, therefore, they are not capable of forming stud or cruciform structures. The sequences of this type are detected in almost all large DNA molecules and may include from all multiple base pairs to several thousand base pairs.
The presence of palindromes in the form of cruciform structures in eukaryotic cells is not proved, although a certain amount of cruciform structures detected under in vivo conditions in E. coli cells. The presence in the composition of RNA or single-stranded DNA of self-commercial sequences is the main cause of folding in solutions of the nucleic circuit into a certain spatial structure, characterized by the formation of a set of "spills".
DNA H - This is a spiral, which is formed by three DNA chains - Triple DNA Spiral. It is a complex Watson-Crica dual spiral with a third single-chain DNA thread, which is placed in its large groove, with the formation of the so-called Hugstin couple.
The formation of a similar triplex occurs as a result of the addition of double-spiral DNA in such a way that half of its site remains in the form of a double helix, and the second half is separated. In this case, one of the disconnected spirals forms a new structure with the first half double spiral - a triple spiral, and the second is unstructured, in the form of a one-way area. A feature of this structural transition is a sharp dependence on the pH of the medium, the protons of which stabilize the new structure. Due to this feature new Structure Received the name of the H-form DNA, the formation of which was found in superpiralized plasmids containing homopurine-homopyrimidine areas, which are a mirror replay.
In further research, the possibility of the structural transition of some homopurine-homopyrimidine bindel polynucleotides was established to form a three-dimensional structure containing:
- one homopurine and two homopyrimidine threads ( PY-PU-PY Triplex) [Hugstin interaction].
The components of the PY-PU-PY Triplex blocks are canonical isomorphic CGC + and TAT triads. Triplex stabilization requires the protonation of the CGC + triad, so these trips are dependent on the pH of the solution.
- one homopyrimidine and two homopyrin threads ( PY-PU-PU Triplex) [Reverse Hugstin interaction].
The components of the PY-PU-PU Triplex blocks are canonical isomorphic CGG and TAA Taiad. The essential property of PY-PU-PU Triplexes is the dependence of their stability from the presence of two-chain ions, and various ions are needed to stabilize triplexes of different sequences. Since the formation of PY-PU-PU Triplexes does not require protonation of nucleotides included in their composition, such tryplexes may exist with neutral pH.
Note: Direct and inverse Hugstin interaction is explained by 1-methylthine symmetry: the rotation of 180 ° leads to the fact that the O4 atom is occupied by an O2 atom, while the hydrogen bond system is preserved.
Two types of triple spirals are known:
- parallel Triple Spirals, in which the polarity of the third chain coincides with the polarity of the homopyrin chain of Watson Cryovsky Duplex
- anti-parallel triple spirals, in which the polarity of the third and homopuric chains are opposite.
G-quadruplex - 4-spiral DNA. Such a structure is formed if there are four guanin, which form the so-called G-quadruplex - dance of four guanins.
The first hints for the possibility of formation of such structures were received long before the breakthrough work of Watson and the cry - back in 1910. Then the German chemist Ivar Bang found that one of the components of DNA - guanosic acid - at high concentrations, it forms gels, while other components of DNA do not possess such a property.
In 1962, using the X-ray structural method, it was possible to establish the structure of the cell of this gel. It turned out to be composed of four guanin residues that bind each other in a circle and forming a characteristic square. In the center of communication supports metal ion (Na, k, Mg). The same structures can both form in DNA if there is a lot of guanin. These flat squares (G-quartets) are folded into the stacks, and it turns out quite stable, dense structures (G-quadruplexes).
Four separate DNA chains can be gossipped into four separate complexes, but it is rather an exception. More often a single thread of nucleic acid is simply tied to the node, forming characteristic thickening (for example, at the ends of chromosomes), or two-chain DNA on some rich guanin plot forms a local quadruplex.
The existence of quadruplexes at the ends of chromosomes is most studied - on telomeres and oncopromotors. However, it is still a complete picture of the localization of such DNA in human chromosomes is not known.
All of these unusual DNA structures in linear form are unstable compared to the DNA form. However, DNA often exists in the annular form of topological voltage when it has so-called superpioralization. Under these conditions, non-canonical DNA structures are easily formed: Z-forms, "Crosses" and "Studs", H-forms, Guanin Quadruplexes and I-motifs.
- Superpuralized form - noted when the cell is isolated from the core without damage to the pentoso phosphate island. It has the shape of super-shielded closed rings. In the superchangeable state, the DNA double helix at least once "twisted itself", i.e. it contains at least one supervision (takes the shape of the eight).
- The relaxed state of DNA is observed during a single break (break of one thread). At the same time, the winds disappear and the DNA takes the form of a closed ring.
- The linear form of DNA is observed when the double spiral threads break.
Tertiary structure of DNA
Tertiary structure of DNA It is formed as a result of additional twisting in the space of a two-power molecule - its superspiration. Superpirations of DNA molecule in eukaryotic cells, in contrast to prokaryotes, is carried out in the form of complexes with proteins.
Eukarot DNA is almost all in chromosomes of nuclei, only a small amount is contained in mitochondria, and in plants and in plasts. The main substance chromosome of eukaryotic cells (including the human chromosome) is chromatin consisting of two-stranded DNA, histone and non-secretone proteins.
Histon proteins chromatin
Histons are simple proteins, accounted for up to 50% chromatin. In all studied cells of animals and plants, five basic histones classes were found: H1, H2A, H2B, H3, H4, differing in size, amino acid composition and charge value (always positive).
Histon H1 mammals consists of one polypeptide chain containing approximately 215 amino acids; The size of the other histones varies from 100 to 135 amino acids. All of them are spyralized and twisted in a globe with a diameter of about 2.5 nm, contain an unusually large number of positively charged amino acids lysine and arginine. Histons can be acetylated, methylated, phosphorylated, poly (ADP) -Regosilaned, and Histons H2A and H2B are covalently associated with uvilitin. What is the role of such modifications in the formation of the structure and performing functions by histones to the end is not yet found. It is assumed that this is their ability to interact with DNA and provide one of the mechanisms for regulating genes.
Histons interact with DNA mainly through ion ties (Salt bridges) formed between negatively charged DNA phosphate groups and positively charged lysine and arginine residues of histones.
Negiston proteins Chromatin
Ungiston proteins, in contrast to histones, are very diverse. Up to 590 different fractions of DNA-binding nonregone proteins are isolated. They are also called acidic proteins, since acid amino acids are dominated in their structure (they are polyanions). With a variety of non-secretone proteins, the specific regulation of the activity of chromatin is associated. For example, the enzymes needed for replication and DNA expression can communicate with chromatin temporarily. Other proteins, let's say participating in various regulation processes, are associated with DNA only in specific tissues or at certain differentiation stages. Each protein is complementary than a specific DNA nucleotide sequence (DNA website). This group includes:
- family of site-specific proteins like "zinc fingers". Each "zinc finger" recognizes a specific site consisting of 5 nucleotide pairs.
- a family of site-specific proteins - homodimers. The fragment of such a protein in contact with DNA has a "spiral-spiral spiral" structure.
- high mobility proteins (HMG proteins - from English, High Mobility Gel Proteins) - a group of structural and regulatory proteins that are constantly associated with chromatin. They have a molecular weight of less than 30 cd and are characterized by a high content of charged amino acids. Due to the small molecular weight of HMG proteins, they have high mobility during electrophoresis in the polyacrylamide gel.
- replication, transcription and reparation enzymes.
With the participation of structural, regulatory proteins and enzymes involved in the synthesis of DNA and RNA, nucleosomes are converted into a highly condensible protein complex and DNA. The formed structure is 10,000 times shorter than the original DNA molecule.
Chromatin
Chromatin is a complex of proteins with nuclear DNA and inorganic substances. The main part of chromatin is inactive. It contains tightly packaged, condensed DNA. This is heterochromatin. There is a constitutive, genetically inactive chromatin (satellite DNA) consisting of non-expressed areas, and optional - inactive in a number of generations, but under certain circumstances, capable of espressing.
Active chromatin (Euchromatin) is non-condensed, i.e. Packed less tight. In different cells, its content ranges from 2 to 11%. In the cells of the brain, it is most of all - 10-11%, in liver cells - 3-4 and kidneys - 2-3%. There is an active transcription of Euchromatin. At the same time, its structural organization allows the use of the same genetic information of DNA inherent in the body's type, in various cells in specialized cells.
In the electron microscope, the chromatin image resembles beads: spherical thickening of about 10 nm, separated by filamentary jumpers. These spherical thickens are called nucleosomes. Nucleosome is a structural unit of chromatin. Each nucleosome contains a superpiral DNA segment of 146 nucleotide pairs, wound with the formation of 1.75 left turns on the nucleosomal cor. The nucleosomal Cor is a histone octamer consisting of Histons H2A, H2B, H3 and H4, two molecules of each form (Fig. 9), which looks like a disk with a diameter of 11 nm and 5.7 nm thick. The fifth histone, H1, is not part of the nucleosomic bark and does not participate in the process of reducing DNA on the histone octamer. It contacts the DNA in those places where the double helix enters and comes out of the nucleosomal bark. These are interconnect (linker) DNA sections, the length of which varies depending on the type of cells from 40 to 50 nucleotide pairs. As a result, the length of the DNA fragment included in the nucleosome (from 186 to 196 nucleotide pairs) varies.
The nucleosoma includes approximately 90% of DNA, the rest of it falls on the linker. It is believed that nucleosome are fragments of the "silent" chromatin, and the linker is active. However, nucleosome can be deployed and moved to a linear form. Expanded nucleosome are already active chromatin. So clearly manifests the dependence of the function from the structure. It can be considered that the more chromatin is located in the composition of globular nucleosomes, the less active. Obviously, in different cells, the unequal fraction of the restricted chromatin is associated with the number of such nucleosomes.
On electron microscopic photos, depending on the selection conditions and the degree of stretching, the chromatin may look not only like a long thread with thickening - "beads" with nucleosomes, but also as a shorter and more dense fibril (fiber) with a diameter of 30 nm, the formation of which is observed when interacting Histon H1, associated with the Linker section of DNA and Histon H3, which leads to an additional twisting of the spiral of six nucleosomes to the coil with the formation of a solenoid with a diameter of 30 nm. In this case, the histone protein may prevent transcription of a number of genes and thus adjust their activity.
As a result of the DNA interactions described above, the DNA segment of the DNA from 186 bases of bases with an average diameter of 2 nm and a length of 57 nm turns into a helix with a diameter of 10 nm and 5 nm long. With the subsequent compression of this helix to a fiber with a diameter of 30 nm, the degree of condensation increases even six times.
Ultimately, the DNA duplex packaging with five histones leads to 50-fold DNA condensation. However, even so high degree Condensation cannot explain almost 50,000 to 100,000-fold DNA seals in the metaphase chromosome. Unfortunately, the details of the further packaging of chromatin up to metaphase chromosome are not yet known, so you can only be considered general features This process.
DNA compaction levels in chromosomes
Each DNA molecule is packed in a separate chromosome. In the diploid cells of a person contains 46 chromosomes, which are located in the core of the cell. The total length of DNA of all the chromosomes of the cell is 1.74 m, but the diameter of the kernel in which the chromosomes are packed, millions of times less. Such compact DNA laying in chromosomes and chromosomes in the core core is provided with various, histone and non-syston proteins, interacting in a certain sequence with DNA (see above). DNA compaction in chromosomes allows to reduce its linear dimensions of about 10,000 times - conventionally from 5 cm to 5 microns. Several levels of compactization are isolated (Fig. 10).
- dNA double helix - a negatively charged molecule with a diameter of 2 nm and a length of several cm.
- nucleosomal level - Chromatin looks in an electron microscope as a chain "Bead" - nucleosomes - "on the thread". Nucleosome is a universal structural unit, which is found both in euchromatin and in heterochromatin, in the interphase kernel and metaphase chromosomes.
The nucleosomal level of compactization is provided by special proteins - histones. Eight positively charged histone domains form a core (core) of nucleosome on which a negatively charged DNA molecule is wound. This gives shortening at 7 times, while the diameter increases from 2 to 11 nm.
- solenoid level
The solenoid level of the organization chromosomes is characterized by twisting of the nucleosomal thread and the formation of more thick fibrils of 20-35 nm in diameter - solenoids or superbids. The pitch of the solenoid is 11 nm, one of the round accounts for about 6-10 nucleosomes. The solenoid packaging is considered the most likely than the super-bidden, according to which the chromatin fibril with a diameter of 20-35 nm is a chain of granules, or superbid, each of which consists of eight nucleosomes. In the solenoid level, the linear size of DNA is reduced by 6-10 times, the diameter increases to 30 nm.
- loop level
The loopback level is provided by non-secretone site-specific DNA-binding proteins, which recognize certain DNA sequences and are associated with them, forming a loop of about 30-300 thousand base pairs. The loop ensures the expression of genes, i.e. The loop is not only a structural, but also functional education. Shortening at this level occurs at 20-30 times. The diameter increases to 300 nm. The loop-like structures of the type "tube brushes" in the ocytes of amphibians can be seen on cytological preparations. These loops apparently superspiralized and are DNA domains corresponding to probably, chromatin transcription and replication units. Specific proteins fix the bases of the loops and, possibly, some of their internal sections. The loop-shaped domain organization contributes to the chromatin laying in metaphase chromosomes into high-order spiral structures.
- domain level
The domain level of the organization chromosome is not sufficiently studied. At this level, there is a formation of loop domains - structures of threads (fibrils) with a thickness of 25-30 nm, which contain 60% protein, 35% DNA and 5% RNA are practically not visible in all phases of the cell cycle with the exception of mitosis and several randomly distributed by Cell kernel. The loop-like structures of the type "tube brushes" in the ocytes of amphibians can be seen on cytological preparations.
Looped domains are attached to an internal protein matrix in the so-called built-in attachments, often indicated as Mar / Sar-Sequence (MAR, from the English. Matrix Associated Region; SAR, from English SCAFFold Attachment Regions) - DNA fragments with a length of several hundred Base pairs that are characterized by a high content (\u003e 65%) a / t pairs of nucleotides. Each domain, apparently, has one point of starting replication and functions as an autonomous superpiece unit. Any loop domain contains multiple transcription units, the functioning of which is probably coordinated - the entire domain is either in active or in inactive state.
At the domain level, as a result of the sequential chromatin packaging, a decrease in the linear dimensions of DNA is approximately 200 times (700 nm).
- chromosomal level
On the chromosomal level, the contamination chromosome is condensation in metaphase with a seal of looped domains around the axial frame of nonregistone proteins. This superspiration is accompanied by phosphorylation in the cell of all H1 molecules. As a result, the metaphase chromosome can be depicted in the form of tightly laid solenoid loops, rolled into the tight spiral. A typical human chromosome can contain up to 2600 loops. The thickness of such a structure reaches 1400 nm (two chromatids), and the DNA molecule is shortened in 104 times, i.e. With 5 cm stretched DNA up to 5 microns.
Functions chromosomes
In interaction with non-chromosomous chromosome mechanisms provide
- storage of hereditary information
- use of this information to create and maintain a cell organization
- regulation of reading hereditary information
- self-sender genetic material
- the transfer of genetic material from the mother cell is a subsidiary.
There are evidence that when activating the chromatin section, i.e. When transcription, the Histon H1 is reversibly removed from it, and then the Giston Ocet. This causes chromatin decondence, the sequential transition of the 30-nanometer chromatin fibrils into a 10-nanometer thread and its further unfolding into the sections of free DNA, i.e. Loss of the nucleosomal structure.
15.04.2015 13.10.2015
Features of the structure and functionality of "double spiral"
It is difficult to submit a person without genetic habits, features, hereditary changes in the organism of the newborn. It turns out that all information is encoded in the notorious genes, which are carriers of the nucleotide genetic chain.
DNA opening history
The structure of the DNA molecule was known to the world in 1869. I.F. Misher brought the known DNA known for all, which consists of cells, or rather molecules responsible for the transmission of the genetic code for the development of living organisms. Initially, this substance was called nuclein, no one could determine the number of chains of the structure, their operation methods.
Today, scientists finally brought the composition of DNA, which includes 4 types of nucleotides, which, in turn, contains:
· The remains of phosphorus N3RO4;
· Peptose C5H10O4;
· Nitrogen base.
All these elements are in the cell and are part of the DNA and are connected to a double helix, which was removed by F. Screech, D. Watson in 1953. Their studies committed a breakthrough in the world of science and medicine, the work has become the basis for many scientific research, opened the gates to know the genetic heredity of every person.
Structure of compounds
DNA molecule is located in the kernel, performing many different functions. Despite the fact that the main role of the substance is the storage of gene information, the compounds are responsible for the following types of work:
· Encoded amino acid;
· Control the work of the cell cells;
· We produce proteins for external manifestation of genes.
Each part of the compound forms spiral threads, so-called chromatids. The structural units of the spiral are nucleotides that are in the middle of the chain and allow DNA to double. This happens in this way:
1. Thanks to the special enzymes in the cell cage, the spiral is performed.
2. Hydrogen bonds disagree, freeing the enzyme - polymeraz.
3. The parental DNA molecule is connected to a single-chain fragment of 30 nucleotides.
4. Two molecules are formed, in which one thread is the motherboard, the second is synthetic.
What are the nucleotide chains still wrap around the threads? The fact is that the number of enzymes is very large, and thus, they are unhindered on the same axis. Such a phenomenon is called spiralization, the threads are shortened several times, sometimes up to 30 units.
Molecular genetic methods for using DNA in medicine
DNA molecule, made it possible to humanity to use the structure of nucleotide compounds in various directions. First of all, for the diagnosis of hereditary diseases. For monogenic diseases as a result of a coupling inheritance. When identifying the history of infectious, oncological excesses. As well as in forensic medicine to identify the personality.
DNA use of a lot, today there is a list of monogenic diseases, which came out of the mortal list, thanks to the concept of the development of buildings and diagnostics of the molecular biofield. In the future, we can talk about the "newborn genetic document", which will contain the entire list of common individual diseases.
All molecular genetic processes have not yet been studied, it is a rather complicated and laborious mechanism. Perhaps many genetic diseases will be able to prevent in the near future, changing the structure of the birth of a person's birth life!
What else is scheduled for the future based on this substance?
Computer programs based on nucleotide threads have rainbow prospects for creating ultramic computing robots. The ancestor of such an idea is L. Admeman.
The idea of \u200b\u200bthe invention is as follows: For each thread, the sequence of molecular bases that are mixed between themselves and form various RNA options. Such a computer will be able to perform data with an accuracy of 99.8%. According to optimist scientists, such a direction will soon cease to be exotic, and after 10 years will become visible reality.
Improving DNA computers will be in living cells, performing digital programs that will interact with the biochemical processes of the body. The first schemes of such molecules have already been invented, it means that mass production will soon begin.
Amazing and extraordinary facts about DNA
An interesting historical fact suggests that many years ago "Homo Sapires" broke with Neanderthals. The information was confirmed by B. medical center Italy, where the mitochondrial DNA found was determined, which was alleged 40,000 years. She inherited him from generation of people mutants, which many years ago disappeared from the planet Earth.
Another fact narrates about the composition of DNA. There are cases when pregnancy is encouraged as twins, but one of the embryos 
"Draws into yourself" another. This means that there will be 2 DNA in the body of a newborn. Such a phenomenon is known to many of the pictures of the history of Greek mythology, when the organisms had several parts of the body of different animals. To date, many people live and do not know that there are carriers of two structural compounds. Even genetic studies can not always confirm this data.
ATTENTION: There are amazing creatures in the world, whose DNA are eternal, and the specialists are immortal. Is it so? The theory of aging is very difficult. Speaking simple words, with each division, the cell loses its strength. However, if you have a constant structural thread, then you can live forever. Some lobsters, turtles under special conditions can live for a very long time. But no one has canceled the disease, it is the cause of many long-lived animal deaths.
DNA gives hope for improving the life of every living organism, helping to diagnose heavy ailments, becoming more developed, perfect personalities.
All living on the planet consists of a variety of cells supporting the ordering of their organization at the expense of the genetic information contained in the kernel. It persists, is implemented and transmitted by complex high molecular compounds - nucleic acids consisting of monomeric units - nucleotides. The role of nucleic acids cannot be overestimated. The stability of their structure is determined by the normal life activity of the body, and any deviation in the structure inevitably leads to a change in the cell organization, the activity of physiological processes and the viability of cells in general.
The concept of nucleotide and its properties
Each or RNA is collected from smaller monomeric connections - nucleotides. In other words, nucleotide is a building material for nucleic acids, coenzymes and many other biological compounds that are extremely necessary by the cell in the process of its livelihoods.
The basic properties of these essential substances can be attributed:
Storage of information about and inherited features;
. carrying out control over growth and reproduction;
. Participation in metabolism and many other physiological processes occurring in a cell.
Speaking of nucleotides, it is impossible not to stay on such an important questionAs their structure and composition.
Each nucleotide consists of:
Sugar residue;
. nitrogenous base;
. Phosphate group or phosphoric acid residue.
It can be said that nucleotide is a complex organic compound. Depending on the species composition of nitrogenous bases and the type of pentoses in the structure of nucleotide, nucleic acids are divided into:
Deoxyribonucleic acid, or DNA;
. Ribonucleic acid, or RNA.
Composition of nucleic acids
In nucleic acids, sugar is represented by pentose. This is a five-carbon sugar, it is called deoxyribose into DNA, in RNA - ribose. Each pentose molecule has five carbon atoms, four of them together with an oxygen atom form a five-membered ring, and the fifth enters the N-CH2 group.
The position of each carbon atom in the pentose molecule is denoted by the Arabic Digger with the Stroke (1C', 2C', 3C', 4C', 5C' '). Since all the processes of reading with a nucleic acid molecule have a strict orientation, the numbering of carbon atoms and their location in the ring serve as a sign of the correct direction.
According to the hydroxyl group to the third and fifth carbon atoms (3 ° C and 5С'), the residue of phosphoric acid is attached. It determines the chemical affiliation of DNA and RNA to the acid group.
A nitrogen base is attached to the first carbon atom (1С') in the sugar molecule.
Species composition of nitrogen bases
DNA nucleotides on a nitrogen base are represented by four types:
Adenine (a);
. Guanin (D);
. cytosine (C);
. Timine (T).
The first two belong to the Purin class, the last two - pyrimidines. By molecular weight, purin is always heavier than pyrimidine.
Nucleotide RNA on a nitrogen base is presented:
Adenine (a);
. Guanin (D);
. cytosine (C);
. Uracil (y).
Uracil as well as Timin is a pyrimidine base.
IN scientific literature Often you can meet another designation of nitrogenous bases - Latin letters (A, T, C, G, U).
Read more chemical structure Purinov and Pyrimidines.
Pyrimidines, namely cytosine, thymine and uracil, in its composition are represented by two nitrogen atoms and four carbon atoms forming a six-membered ring. Each atom has its own number from 1 to 6.
Purines (adenin and guanine) are consisting of pyrimidine and imidazole or two heterocycles. Purin base molecule is represented by four nitrogen atoms and five carbon atoms. Each atom is numbered from 1 to 9.
As a result of the compound of nitrogenous base and the residue of the pentose, nucleoside is formed. Nucleotide is a compound of nucleoside and phosphate group.
The formation of phosphodieter connections
It is important to understand the question of how nucleotides are connected into a polypeptide chain and form a nucleic acid molecule. This is due to the so-called phosphodieter connections.
The interaction of two nucleotides gives dinucleotide. The formation of a new compound occurs by condensation, when there is a phosphodiestic connection between the phosphate residue of one monomer and the hydroxy group of other pentoses.
The synthesis of polynucleotide is a repeated repetition of this reaction (several million times). The polynucleotide chain is based on the formation of phosphodieter bonds between the third and fifth carbon of the Sahars (3С' and 5C'''''''').
The polynucleotide assembly is a complex process flowing with the participation of the DNA polymerase enzyme, which provides a chain growth only from one end (3') with a free hydroxy group.
DNA molecule structure
DNA molecule, as well as protein, may have a primary, secondary and tertiary structure.
The sequence of nucleotides in the DNA circuit determines its primary is formed by hydrogen bonds, the occurrence of which is the principle of complementation. In other words, the synthesis of double acts a certain pattern: adenine of one chain corresponds to the thyme of another, guanine - cytosine, and vice versa. Pair of adenine and thymine or guanin and cytosine are formed due to two in the first and three in the latter case of hydrogen bonds. Such a connection of nucleotides provides a solid connection of chains and an equal distance between them.
Knowing the nucleotide sequence of one DNA chain, according to the principle of complementarity or additions, you can count the second.
The tertiary structure of DNA is formed due to complex three-dimensional bonds, which makes it a more compact and capable of placing in a small amount of cell. So, for example, DNA length intestinal sticks It is more than 1 mm, while the cell length is less than 5 microns.
The number of nucleotides in DNA, namely their quantitative relation, is subject to the rule of Chergaff (the number of purine bases is always equal to the amount of pyrimidine). The distance between nucleotides is a permanent value of 0.34 nm, as well as their molecular weight.
RNA molecule structure
RNA is represented by one polynucleotide chain formed through a pentose (in this case by ribose) and phosphate residue. In length, it is significantly shorter than DNA. According to the species composition of nitrogenous bases in the nucleotide there are also differences. In RNA, instead of the pyrimidine base of thymine, Uracil is used. Depending on the functions performed in the body, RNA can be three types.
Ribosomal (RDNA) - it usually contains from 3000 to 5000 nucleotides. As necessary structural component Takes part in the formation of an active center Ribosoma, the place of implementation of one of the most important processes in the cell - protein biosynthesis.
. Transport (TRNA) - consists on an average of 75 - 95 nucleotides, transfers the desired amino acid to the place of synthesis of the polypeptide in the ribosome. Each type of TRNA (at least 40) has its own inherent sequence of monomers or nucleotides.
. Information (IRNA) - on the nucleotide composition is very diverse. Transfer genetic information from DNA to ribosomes, acts as a matrix for the synthesis of a protein molecule.
The role of nucleotides in the body
Nucleotides in the cell perform a number of essential functions:
Used as structural blocks for nucleic acids (purine and pyrimidine nucleotides);
. participate in many metabolic processes in the cell;
. included in the ATP - the main source of energy in the cells;
. act as carriers of reducing equivalents in cells (above +, NADF +, FAD, FMN);
. perform the function of bioregulators;
. As the second messengers of extracellular regular synthesis (for example, CAMF or CGMF) are considered.
The nucleotide is a monomeric unit forming more complex compounds - nucleic acids, without which genetic information is not possible, its storage and playback. Free nucleotides are the main components involved in signaling and energy processes supporting the normal vital activity of cells and the body as a whole.
DNA is one of two types of nucleic acids - deoxyribonucleic (DNA) and ribonucleic (RNA). These biopolymers consist of monomers called nucleotides. DNA nucleotide monomers and RNA are similar in the main features of the structure. Each nucleotide consists of three components connected by durable chemical bonds
Nucleotides that are part of DNA contain five-carbon sugar - deoxyribozo, one of four nitrogen bases: adenine, guanine, cytosine, thymine (A, G, C, T) and phosphoric acid residue.
In the composition of nucleotides to the ribose molecule (or deoxyribose), a nitrogen base is attached on one side, and on the other - the residue of phosphoric acid. Nucleotides are connected to long chains. The axles of such a chain form regularly alternating sugar residues and organic phosphates, and the lateral groups of this chain are four types of irregular alternating nitrogen bases.
The DNA molecule is a structure consisting of two threads, which along the entire length are connected to each other hydrogen bonds. Such a structure characteristic of only DNA molecules is called a double helix. A feature of the DNA structure is that against one nitrogen base in one chain lies a strictly defined nitrogen base in another chain - these pairs of bases are called complimentary bases (complementary by each other): a \u003d t; G C.
A set of proteins (enzymes, hormones, etc.) determines the properties of the cell and the body. DNA molecules keep information about these properties and transmit them to generation of descendants.
DNA was opened by Johann Friedrich Misher in 1869. Initially, the new substance got a name nuclein, and later, when Misher has determined that this substance has acid properties, the substance got a name nucleic acid . Biological function The newly open substance was unclear, and for a long time DNA was considered a member of phosphorus in the body. Moreover, even at the beginning of the XX century, many biologists believed that DNA had nothing to do with information transferSince the structure of the molecule, in their opinion, was too monotonous and could not contain encoded information.
Gradually it was proved that it was DNA, and not proteins, as previously thought, is a carrier of genetic information. One of the first decisive evidence was brought by O. Every experiments, Colin Mac-Lododa and Maclin McClap (1944) on the transformation of bacteria. They managed to show that for the so-called transformation (the acquisition of the pathogenic properties of the harmless culture as a result of the addition of dead pathogens) is responsible for DNA isolated from pneumococci. Experiment of American scientists Alfred Hershei and Martha Chase (EXPERIMENT HERSHA-CHAIZ, 1952) with labeled radioactive isotopes Proteins and DNA bacteriophages have shown that only nucleic phage nucleic acid is transmitted to the infected cell, and the new generation of phage contains the same proteins and nucleic acid as the initial phage.
Up until the 50s of the 20th century, the exact structure of DNA, as well as the method of transmitting hereditary information remained unknown. Although it was not known that the DNA consists of several chains consisting of nucleotides, no one knew exactly how many of these chains and how they are connected.
DNA double helix structure was proposed by Francis Creek and James Watson in 1953 on the basis of x-ray diffraction data obtained by Maurice Wilkins and Rosalind Franklin, and "Chargaff Rules", according to which there are strict relations in each DNA molecule, which binds the number of nitrous bases of different types . Later, the model of the DNA structure was proven by Watson and scream, and their work was noted Nobel Prize in physiology and medicine 1962 Among the laureates, Franklin's Rosalinda did not live by the time, as the premium is not awarded to posthumously