about the project
Medical news
For authors
Licensed books on medicine
<< Previous Next >>


Nucleic acids were first discovered by I.F. Misher in 1868. He isolated a special substance of an acidic nature from the nuclei of cells and called it nuclein. Subsequently, he was given the name "nucleic acid." Two types of nucleic acids have been discovered. They were named depending on the carbohydrate component in the composition. Nucleic acid, which contains the carbohydrate of deoxyribose, was called deoxyribonucleic acid (DNA), and which contains the carbohydrate of ribose, called ribonucleic acid (RNA). In the period from 1900 to 1932, the chemical composition of nucleic acids was determined. They include the following components:


Purine bases Adenine, guanine Adenine, guanine

Pyrimidine bases cytosine, thymine cytosine, uracil

Carbohydrate component of Deoxyribose Ribose

Both nucleic acids include phosphoric acid residues. The difference lies in the fact that the RNA contains the nitrogenous base uracil instead of thymine and ribose instead of deoxyribose.

In 1936, A. N. Belozersky and I. I. Dubrovskaya first isolated pure DNA from plant material at the Department of Plant Biochemistry of Moscow University. By the mid-40s, it was found that DNA and RNA are simultaneously present in every living organism.

In the late 40s and early 50s, new physical and chemical methods of research began to be used in the study of nucleic acids. In 1950, E. Chargaff established the rules of nucleotide relations that underlie the structure of all DNA.

The rules of Chargaff are that in DNA the content of adenine is equal to the content of thymine (A = T), and the content of guanine is equal to the content of cytosine (G = H), hence A + G / T + C = 1; the sum of purine nucleotides is equal to the sum of pyrimidine nucleotides. In accordance with this rule, the nucleotide composition of different organisms can vary only in magnitude A + T / G + C.

By 1952, R. Franklin and M. Wilkins were able to obtain high-quality x-rays of DNA, which showed that it has a spiral shape and a dual structure.

In 1953, J. Watson and F. Crick, based on the data of X-ray analysis and the rules of Charguff, established the structure of DNA. According to their model, the DNA molecule has a double helix consisting of two polynucleotide chains with a common axis (Fig. 17). The diameter of the double helix of DNA is 2 nm, and the distance between the turns of 3.4 nm. For each coil of the helix there are 10 pairs of nucleotides, hence the distance between the nitrogenous bases is 0.34 nm.

The structural units of polynucleotide chains are nucleotides. The composition of the nucleotide includes: one of the nitrogenous bases - purine (adenine or guanine) or pyrimidine (thymine or cytosine), deoxyribose, phosphate residue. These components are connected to each other in the following order: nitrogen base - deoxyribose - phosphate residue.
The combination of one of the bases with deoxyribose leads to the formation of a nucleoside. When a phosphate group is attached to the carbohydrate moiety of a nucleoside, a nucleotide is formed.

Deoxyribose in nucleotides binds to the bases with a glycoside bond, and with phosphoric acid - through ether bonds. Therefore, in terms of chemical composition, any nucleotide is a phosphoric ester of nucleosides. Accordingly, nucleotides are called deoxyadenylic, deoxyguanilic, deoxycytidyl and thymidyl acids.

Along with the main nitrogenous bases, DNA also contains methylated bases, such as 5-methylcytosine, 5-hydroxymethylcytosine, etc. In animals, the amount of 5-methylcytosine in DNA usually does not exceed 1.5–2%.

In each of the DNA strands, the nucleotides are connected in series with each other using a phosphoric acid residue and a deoxyribose molecule. Deoxyribose binds to one molecule of phosphoric acid through carbon in the 3 'position, and on the other through carbon 5', forming a carbohydrate-phosphate backbone (Fig. 18).

Both chains in the DNA molecule have the opposite polarity. This means that the internucleotide bond in one chain

has a direction of 5 '-> 3', and in the other 3 '-> 5'.

The nitrogenous bases of the nucleotides of both DNA chains are enclosed internally between the turns of the helix and are connected by hydrogen bonds. In accordance with the rules of Chargaff, adenine of one chain is associated only with thymine of the other chain, and guanine is associated only with cytosine. The adenine-thymine pair is connected by two hydrogen bonds, and the guanine-cytosine pair by three. This order of compliance of nitrogen bases (A ** T and G ** D) is called

complementarity, and therefore the chains in DNA are complementary; they complement each other.

The carbohydrate-phosphate backbone along the entire length in all DNA molecules has the same structure and cannot carry genetic information. In contrast, the arrangement of purine and pyrimidine bases of nucleotides along the DNA chain is very variable and characteristic of each given type of DNA molecule. Hence, the hereditary information is encrypted with a different sequence of bases.

The nucleotide composition of DNA varies significantly depending on the membership of an organism to a particular systematic group (Table 7). The specificity of DNA is expressed by the ratio A + T / G + C, called the coefficient of species specificity.

In the DNA of animals there is an excess of A + T with respect to G + C. In fungi and bacteria, forms are found both rich in A + T and with a predominance of G + C, while at the same time there are close animals in terms of specificity. This suggests that the variability in the arrangement of the bases is already sufficient to ensure differences between the genes of these organisms.

DNA molecules consist of approximately 2–10–1–10 or more nucleotides and have a large relative molecular weight.
<< Previous Next >>
= Skip to textbook content =


    Nucdeic acid is a giant polymer molecule built from numerous repeating monomeric units called nucleotides. The nucleotide consists of a nitrogenous base, sugar and a phosphoric acid residue (Fig. IV.2). {foto28} Nitrogen bases are derivatives of one of two classes of compounds - the purine or pyrimidine series (Fig.
  2. The chemical nature of the nucleic acids of viruses
    By their chemical nature, the nucleic acids of viruses do not differ from the nucleic acids of cells (organisms) and are polynucleotide chains formed by the alternation of four deoxyribonucleotides in the case of DNA or ribonucleotides in the case of RNA connected by phosphodiester bonds. The nucleotide is a nitrogenous base (adenosine (A), guanosine (G), cytidine (C),
  3. Evidence of the Genetic Role of Nucleic Acid
    The history of the study of nucleic acids begins in 1869, when the Swiss chemist F. Mischer discovered special substances with acid properties in the cell nucleus. He gave them the name of nucleic acids (from lat. Nukleus - the nucleus). For a long time, nucleic acids did not attract the attention of researchers. And only after the experiments of the English bacteriologist F. Griffith (1928) was demonstrated
    The elemental composition of the cell (protoplasm). To clearly imagine the biological and physicochemical properties of tissues, it is necessary to know the chemical composition of the protoplasm of the cell. In addition to water, there are a large number of elements in the protoplasm. The finest chemical studies have found that out of 104 elements of the periodic system of D. I. Mendeleev, protoplasm contains 96. Four
  5. Nucleic acids, evidence of their role in inheritance
    Genetic information is realized in the process of protein biosynthesis. All the basic properties of living things are determined by the structure and function of protein molecules. Over the past 40 years, a number of laboratories around the world have found that the synthesis of specific proteins is genetically predetermined. The material substrate of heredity is DNA. In DNA molecules, hereditary information about
  7. The chemical composition of water. Water pollution: physical, chemical, bacteriological. Self-cleaning ability of water sources
    The chemical composition of water. In nature, water almost always contains more or less mineral salts dissolved in it. The degree and mineral composition of water is determined by the nature of the soil or soils adjacent to aquifers or surface water sources. The amount of mineral salts contained in the water is expressed in mg / L. Organic matter Of these, the most important
  8. The general chemical composition of viruses
    An indispensable component of a viral particle is any one of the two nucleic acids, protein and ash elements. These three components are common to all viruses without exception, while the remaining two-lipoids and carbohydrates are not all viruses. Viruses consisting only of nucleic acid protein and ash elements most often belong to the group of simple ones, so
    The chemical composition of meat is very complex and depends on the type of animal, age, gender, fatness, level of feeding and other factors. The chemical composition of animal meat changes significantly in severe pathological conditions. The chemical composition of meat includes: water, proteins, fats and lipoids, carbohydrates, extractive substances, minerals, vitamins, enzymes and hormones. Chemical composition
  10. The chemical composition of bone tissue.
    The study of the chemical composition of bone tissue is fraught with considerable difficulties, since the isolation of the organic matrix requires bone demineralization. In addition, the content and composition of the organic matrix are subject to significant changes depending on the degree of bone mineralization. It is known that with prolonged treatment of bones in dilute acid solutions
  11. Soil chemistry
    It has now been established that the human body contains about 60 different chemical elements, which is about 0.6% of the total weight. The presence of trace elements, even in small amounts, is constantly associated with their role in the absorption of nitrogen and photosynthesis. Only to maintain the normal composition of human blood, about 25 microelements are needed, and their composition includes breast milk
    The chemical composition of honey is very complex and diverse (table. 29). It contains over 100 components necessary for the body. These substances can be represented as follows: As can be seen from the table, the main components of honey are fruit (fructose) and grape (glucose) sugar. As a rule, there is more fruit sugar (40%) than grape sugar (35%). Amount of fruit and grape
    Milk consists of more than 300 components, the main of which are water, proteins, fat, lactose, microelements, vitamins, enzymes, hormones, etc. Water is the medium in which all other components of milk are dissolved or distributed, forming a stable colloidal system that allows exposing milk to various technological processes. 95-97% of the water is in a free state. This water can
  14. The chemical composition and nutritional value of cow's milk
    The chemical composition of milk depends on the breed of animals, the lecture period, the nature of the feed, the method of milking. The chemical composition of milk: proteins - 3.2%, fats - 3.4%, lactose - 4.6%, mineral salts - 0.75%, water - 87-89%, dry residue - 11-17%. Milk proteins have high biological value. Their digestibility is 96.0%. Essential amino acids are contained in sufficient quantities and optimal
  15. Chemical composition of air
    and oxygen СО2 (carbon dioxide) N2 (nitrogen) Inert gases and impurities 20.94% 0.03-0.04% 78.1% 1% The biological significance of oxygen lies in participation in respiration, which is necessary for oxidative processes in the body. A person absorbs 12 liters of oxygen per hour or 6-7 liters of air per minute, athletes - up to 120 liters per hour. It is given by: - ​​atmosphere - green (chlorophyll) plants. Indoors
  16. The chemical composition and structure of grain
    Cereal products occupy a large place in the diet and make up about 50% of the daily energy value of the food rations of the population of most regions of our country. Grain is a raw material for many branches of the food industry and is used in animal husbandry as feed. The population’s diet uses grain from crops such as rye, wheat, barley, buckwheat, rice, oats,
  17. Chemical composition of air
    Atmospheric air is a mixture of various gases. It contains constant atmospheric components (oxygen, nitrogen, carbon dioxide), inert gases (argon, helium, neon, krypton, hydrogen, xenon, radon), small amounts of ozone, nitrous oxide, methane, iodine, water vapor, and in varying amounts, various impurities of natural origin and pollution generated in
    By caloric value and taste, fish meat is not inferior to meat of warm-blooded animals. Almost the whole body of the fish goes into culinary processing, except for internal organs, with the exception of caviar and cod liver. In the manufacture of canned food, the content of edible parts increases due to bones, which, after processing, are edible. The nutritional value of fish is determined by the content of high-grade proteins, fat,
    Depending on the type of wild animals, their meat differs in organoleptic characteristics, morphological and chemical composition, taste and culinary qualities. In meat of young animals, unlike meat of adults, less fat and more loose connective tissue. Fat in wild animals is deposited under the skin, in the pelvic cavity, in the lumbar, near the kidneys and only with high fatness in
  20. Morphological structure and chemical composition of chromosomes
    Microscopic analysis of chromosomes primarily shows their differences in shape and size. The structure of each chromosome is purely individual. You can also notice that chromosomes have common morphological characteristics. They consist of two strands - chromatids, arranged in parallel and interconnected at one point, called the centromere or primary constriction. On some chromosomes
Medical portal "MedguideBook" © 2014-2019