More recently, a significant breakthrough has occurred in microbiology and genetics that has affected science. Almost completely decoded the structure of DNA. The decoding of information was analyzed, new methods for decoding the molecule were developed and introduced, and knowledge began to be effectively applied in practice. The article provides general information about DNA.
Story
Nucleic acids began to be studied in the nineteenth century. Friedrich Miescher in 1868 was the first to isolate nuclein from cells, which was later called deoxyribonucleic acid - DNA. However, at that time, the discovery was treated rather skeptically and the molecule was not given much importance. Only in the middle of the twentieth century, thanks to experiments on mice by O. Avery and F. Griffith, a radical change occurred. When studying the transformation of bacteria, it turned out that the DNA molecule was responsible for this process.
Later, R. Franklin accidentally used X-rays to study the structure of crystals, thanks to which she was able to take a photograph of DNA. Based on this, in 1953 the principle of self-replication, as well as the reproduction of life on Earth, was formulated.
DNA - composition
DNA is made up of deoxyribonucleic and ribonucleic acids. Biopolymers consist, in turn, of monomers, or nucleotides, containing three components, firmly interconnected by chemical bonds.
DNA nucleotides contain a five-carbon sugar attached to the molecule from a nitrogenous base (adenine, guanine, cytosine, thymine) on one side and a phosphoric acid residue on the other. They are connected in long chains.
The structure of DNA consists of two strands connected by hydrogen bonds. They are called the double helix. Such a structure exists only in the DNA molecule. In it, against one nitrogen base in one chain, there is a certain base in the other. Such pairs are called complementary, that is, complementary.
human genome
A huge amount of information is contained in just one DNA molecule. Its formula is a line of capital letters of the name of the peptides. This is the genetic code, that is, the sequence of nucleotides inherent in a particular person.
The human genome was discovered in 2001. But the full picture was presented to the world only in 2007. The project, which began in 1990, touched upon the social, ethical and even moral aspects of human life. By 2003, the code was 99.99% decrypted. Therefore, even today there is still an incomplete clarity of the process. But scientists consider this fraction of a percent to be an insignificant minus.
Opening value
DNA is responsible for heredity. Decoding makes it possible to study the development and life of any terrestrial organism, and the intervention of doctors today can slightly change the processes inherent in the molecule.
If there is a DNA code, deciphering it will allow the doctor to identify various diseases that may occur in a person, predict their course and select medicines.
And to this day there has not yet been a complete understanding of what it means to decode a molecule. Thanks to this, for example, it became known that Neanderthals could talk and did not suffer from schizophrenia and Down syndrome.
The DNA molecules in humans are virtually the same. Replacing the nitrogenous bases in them can lead to mutations and diseases. Although sometimes there is only a predisposition to them, and if a person is not subject to bad habits, he will be able to avoid their appearance.
Doctors already know five thousand diseases (many of which lead to disability) that are transmitted through DNA. Deciphering the molecule will warn people about the predisposition. Then the person will take preventive measures so that the disease does not develop. Since the human genotype does not change with age, it is enough to take tests once.
Technologies today help to reveal the abilities of a person up to the calculation of optimal physical activity, effective muscle building and rapid weight loss.
The study of DNA advances the level of microbiology that deals with viruses, fungi, and bacteria that cause infections in humans. Thanks to this, industries such as biopharmaceuticals, food, cosmetics, environmental monitoring and others receive a new impetus for their development.
ATTENTION!!! THIS MATERIAL HAS BEEN REVISED, ADDED AND INCLUDED IN THE BOOK “Creation or Evolution? How old is the Earth? PLEASE GO TO THE PAGE TO READ -->
To be convinced of the absurdity of spontaneous generation, let's see how the microcosm works. Note that we will consider it only superficially, since it is too complicated.
A cell is an elementary unit of structure and vital activity of all living organisms. It has its own metabolism, is capable of independent existence, self-reproduction and development. Each cell is a city in miniature, consisting of power plants, overpasses, treatment facilities, etc. A cell consists of a nucleus, membrane, cytoplasm, chromosomes, ribosomes, DNA, RNA, proteins and many other elements, each of which, in turn, has its own microcosm. Naturally, a cell can exist and perform its functions if all these structures are created simultaneously.
A protein molecule (protein) consists of 50 - 40,000 amino acids interconnected.
Rice. The principle of the structure of a protein from amino acids
Moreover, the diversity of protein structures created from 20 types of amino acids cannot be overestimated. So, a chain of 100 amino acids (a small protein) can be represented in more than 10 to the 130th power, in other words, 10 and 130 zeros. For example: in the oceans there are 10 to the 40th degree of water molecules (10 and 40 zeros). Moreover, the location of each amino acid in the protein structure is of great importance, as in a computer program. If at least one element is rearranged, the protein molecule will not work, which means it will not be able to function and fulfill its purpose, and the cell, that is, the part of the body in which cells with these proteins are needed, will not work. Imagine how negligible is the possibility of the spontaneous appearance of the simplest protein, and even more so the specific one that is needed by the cell and, as a result, the body! But for the functioning of the simplest cells and organisms, thousands of different proteins are needed.
Without ribosomes and RNA, amino acids cannot combine into a protein, especially in the one that is needed at this stage in a particular cell. The RNA takes the information about this desired protein from the DNA, and the ribosomes act as a building block.
Rice. Protein synthesis in a cell
In a DNA molecule of human chromosomes, there are from 50 to 245 million complexly arranged pairs of nitrogenous bases. Biochemists have calculated that in 1 DNA molecule there are 10 to the 87th degree possible combinations of the material in it. And only one option will allow you to create you personally - with all properly functioning organs and individual qualities. Materialistic scientists believe that the earth is 4.5 billion years old. This period of time corresponds to 10 to the 25th power of seconds. That is, if one variant of DNA is invented every second, then the age of the Earth will not be enough to create one functioning DNA. But it's not just the sheer complexity of DNA. The fact is that DNA is a program that can be compared to a computer code. Only this code surpasses the programs created by man in its size and complexity. The famous programmer Bill Gates said this about DNA: "Human DNA is like a computer program, only infinitely more perfect." Think about it, since there is a program, then a reading mechanism is also needed, otherwise any program is just garbage. So, DNA also contains a code for creating a mechanism for reading information from itself and further building the whole organism according to this program. It is written in DNA where and at what time a certain protein and other elements should be created in a person. From one cell in which DNA is located, the self-construction of any organism begins. The structure of the DNA molecule allows it to divide. It consists of two parallel identical strands of nucleotides linked by a weak chemical hydrogen bond. When the molecule divides, the chain breaks, leaving all the information in each of the resulting new cells.
Rice. DNA structure
Who created the material for the cell? Who connected this material into a cage? Who came up with different - different from each other, designed for different functions, but necessary for each organism cells. Who wrote the information in the form of a program in DNA? Who created the mechanism for reading and executing this information? A scientific documentary filmed about the ingenious complexity of the cell " Miracle in a cage (miracle in a cage)", in which it is shown in the form of animation what extremely complex processes take place inside the cell. There are many videos about this "Cell Life", "Cell World", etc. To analyze Darwin's theory, you need to understand that in those days science could see only large bacteria, and the cell was presented to people as a tiny container with a liquid.Moreover, they knew nothing about microbiology and genetics.
Today, many scientists are aware of the incredible complexity of the structure of the cell and the whole organism. Some of them are on the side of the creationists. But many believe in chance. Thus, we see not the confrontation of scientists against religion, but two religions - 1) faith in God and creation, and 2) faith in the accidental happy birth of life and its further self-development. But even simple reason is enough to understand the practical impossibility of the latter. Think about how millions of inanimate elements, with the help of chemical bonds, organized themselves into complex huge structures of DNA, RNA, ribosomes, proteins, etc., following a strictly defined sequence (including a program), and then, "thinking through" and "distributing" interactions with each other, surrounding themselves with a shell, created a living organism out of itself - a cell with a huge variety of possibilities and functions. How then the cells, dividing, did not spread into jelly, but created separate organs, tissues, bones, blood vessels, the brain, which, interacting with each other in a complex way, formed a viable and capable of self-reproducing organism. Where did the masculine and feminine come from? If we assume that we evolved from an amoeba, then the fission theory would be more correct. How, in the process of evolution within a species, did its representatives gradually divide into male and female, while maintaining viability and acquiring the ability to uniquely reproduce their own kind, and even in different ways (internal, external, double fertilization ...)? How did new creatures, for example, mammals, come into being when the structure of the female and male organisms was still in the process of separation and development? After all, underdeveloped spermatozoa, eggs and the uterus are simply not able to create a living being. How different-sex creatures and their organs developed in parallel while being viable. Today we see that even a small deviation or disease in the sperm, eggs and uterus makes a person infertile. And speaking of evolutionary development, the gradual improvement of everything, both external and internal, including the organs of reproduction, is simply inevitable. How did underdeveloped creatures with underdeveloped reproductive organs reproduce, and how did intermediate forms reproduce? The materialists do not have answers to these questions, and cannot be.
Here it is appropriate to recall a rhetorical question to which materialists will never be able to find an answer: "What was earlier the chicken or the egg?". Despite the seeming comical question, he is very serious. The chicken could not have come into being without the egg, the perfect device for the formation of the embryo, the growth of the embryo and its development into a chicken. So the egg could not suddenly appear out of nowhere without a chicken. This mutually exclusive analogy is superimposed on other controversial points in the materialistic theory of evolution. As noted above, any organism has DNA, which contains all the information about it. Without this ready-made DNA with information embedded in it, this perfect organism would not exist. So DNA can only be taken from an already created creature.
Sir Fred Hoyle, professor of astronomy at Cambridge, devoted much of his time to the mathematical calculation of the possibility of the accidental origin of life and subsequently stated: “It is more likely that a tornado rushing through a junkyard can assemble a Boeing 747 from trash raised into the air than from inanimate nature can arise alive."
Therefore, science still cannot give a repeating example of the spontaneous generation of life!
CELL, MOLECULE, DNA - THE HUMAN MICROWORLD, LIFE INSIDE THE ORGANISM
The radiocarbon method is wrong
Earth's magnetic field is weakening
"Pierced" layers
Soil erosion at the initial level
The moon is less than 10,000 years old
Population Growth Corresponds to the Biblical Age of the Earth
Moon close to Earth
Ice rings show not years
The coral reef has been growing for less than 5,000 years
Dinosaurs are reliable witnesses
All humans are descended from the same pair
Civilizations and writing less than 5,000 years old
The layers of the Earth do not have their own dating. Geological layers. Geological scale
Lack of scientific evidence. Kent Hovind
Deoxyribonucleic acid A polymer is made up of nucleotides.
Nucleotide DNA is made up of
- nitrogenous base (4 types in DNA: adenine, thymine, cytosine, guanine)
- deoxyribose monosugar
- phosphoric acid
Nucleotides are linked together by a strong covalent bond through the sugar of one nucleotide and the phosphoric acid of another. It turns out polynucleotide chain.
Two polynucleotide chains are connected to each other by weak hydrogen bonds between nitrogenous bases according to the rule complementarity: thymine is always opposite to adenine, guanine is always opposite to cytosine (they match each other in the form and number of hydrogen bonds - there are two bonds between A and T, between C and G - 3). It turns out a double strand of DNA, it twists into double helix.
Function of DNA
DNA is part of the chromosomes, stores hereditary information (about the signs of the organism, about the primary structure of proteins).
DNA is capable of self-doubling (replication, reduplication). Self-doubling occurs in interphase before fission. After duplication, each chromosome consists of two chromatids, which during the future division will turn into daughter chromosomes. Due to self-duplication, each of the future daughter cells will receive the same hereditary information.
Differences between RNA and DNA in structure
- ribose instead of deoxyribose
- no thymine, uracil instead
- single stranded
Types of RNA
- information (matrix) RNA
- transfers information about the structure of the protein from the nucleus (from DNA) to the cytoplasm (to the ribosome);
- least in the cell;
- transfer RNA
- transports amino acids to the ribosome;
- the smallest, has the shape of a clover leaf;
- ribosomal RNA
- is part of the ribosome;
- largest in size and quantity
Tasks for the rule of complementarity
There is as much thymine in DNA as there is adenine, the rest (up to 100%) falls on cytosine and guanine, they are also equally divided. For example: if guanine is 15%, then cytosine is also 15%, total 30%, which means that adenine and thymine account for 100-30=70%, hence adenine 70/2=35% and thymine is also 35%
Choose one, the most correct option. What process during mitosis produces daughter cells with a set of chromosomes equal to the parent?
1) the formation of chromatids
2) spiralization of chromosomes
3) dissolution of the nuclear envelope
4) division of the cytoplasm
Answer
Consider a drawing depicting a fragment of a biopolymer molecule. Determine (A) what serves as its monomer, (B) as a result of which process the number of these molecules in the cell increases, (C) what principle underlies its copying. For each letter, select the appropriate term from the list provided.
1) complementarity
2) replication
3) nucleotide
4) denaturation
5) carbohydrate
6) broadcast
7) transcription
Answer
All of the features listed below, except for two, are used to describe the molecule of organic matter shown in the figure. Identify two signs that “fall out” from the general list, and write down the numbers under which they are indicated.
1) performs an enzymatic function
2) stores and transmits hereditary information
3) consists of two nucleotide chains
4) in complex with proteins forms chromosomes
5) participates in the translation process
Answer
Establish a correspondence between the characteristics of a nucleic acid molecule and its type: 1) tRNA, 2) DNA. Write the numbers 1 and 2 in the correct order.
A) consists of one polynucleotide chain
B) transports amino acids to the ribosome
B) consists of 70-80 nucleotide residues
D) stores hereditary information
D) capable of replication
E) is a spiral
Answer
NUCLEOTIDE FROM ANOTHER PAIR
1. In DNA, nucleotides with thymine account for 23%. Determine the percentage of nucleotides with guanine that make up the molecule. Write down the corresponding number in your answer.
Answer
2. In DNA, nucleotides with cytosine account for 13%. Determine the percentage of nucleotides with adenine that make up the molecule. Write down only the appropriate number in your answer.
Answer
3. In DNA, nucleotides with adenine account for 18%. Determine the percentage of nucleotides with cytosine that make up the molecule. Write down only the appropriate number in your answer.
Answer
4. In DNA, nucleotides with thymine account for 36%. Determine the percentage of nucleotides with guanine that make up the molecule. Write down only the appropriate number in your answer.
Answer
5. In DNA, nucleotides with thymine account for 28%. Determine the percentage of nucleotides with guanine that make up the molecule. Write down only the appropriate number in your answer.
Answer
NUCLEOTIDE FROM THE SAME PAIR
1. A fragment of a DNA molecule contains 15% adenine. How much thymine is in this DNA fragment? In response, write down only the number (percentage of thymine).
Answer
2. In a certain DNA molecule, nucleotides with guanine account for 28%. Determine the percentage of nucleotides with cytosine that make up this molecule. Write down only the appropriate number in your answer.
Answer
3. In a certain DNA molecule, nucleotides with adenine account for 37%. Determine the percentage of nucleotides with thymine that make up this molecule. Write down only the appropriate number in your answer.
Answer
NUCLEOTIDE - SUM OF ONE PAIR
1. What percentage of nucleotides with adenine and thymine does the DNA molecule contain in total if the proportion of its nucleotides with cytosine is 26% of the total? Write down only the appropriate number in your answer.
Answer
2. In DNA, nucleotides with cytosine account for 15%. Determine the percentage of nucleotides with thymine and adenine in the amount that make up the molecule. Write down only the appropriate number in your answer.
Answer
SUM OF ONE PAIR - NUCLEOTIDE
1. What is the percentage of nucleotides with adenine in a DNA molecule if nucleotides with guanine and cytosine together make up 18%? Write down only the appropriate number in your answer.
Answer
2. In DNA, nucleotides with guanine and cytosine account for 36%. Determine the percentage of nucleotides with adenine that make up the molecule. Write down only the appropriate number in your answer.
Answer
3. In a certain DNA molecule, the total share of nucleotides with adenine and thymine is 26%. Determine the percentage of nucleotides with guanine that make up this molecule. Write down only the appropriate number in your answer.
Answer
4. In a certain DNA molecule, the total share of nucleotides with cytosine and guanine is 42%. Determine the percentage of nucleotides with adenine that make up this molecule. Write down only the appropriate number in your answer.
Answer
5. In a certain DNA molecule, nucleotides with adenine and thymine account for 54% in total. Determine the percentage of nucleotides with cytosine that make up this molecule. Write down only the appropriate number in your answer.
Answer
SUM OF DIFFERENT PAIRS
1. A fragment of a DNA molecule contains 10% thymine. How many adenine and guanine are in this DNA fragment? In response, write down only the amount of adenine and guanine in total.
Answer
2. In DNA, nucleotides with thymine account for 35%. Determine the percentage of nucleotides with cytosine and adenine in the amount that make up the molecule. Write down only the appropriate number in your answer.
Answer
Choose three options. How is a DNA molecule different from an mRNA molecule?
1) capable of self-doubling
2) cannot self-doubling
3) participates in matrix-type reactions
4) cannot serve as a template for the synthesis of other molecules
5) consists of two polynucleotide strands twisted into a spiral
6) is an integral part of chromosomes
Answer
1. Analyze the table. Fill in the empty cells of the table using the concepts and terms given in the list. For each lettered cell, select the appropriate term from the list provided.
1) uracil
2) construction of the body of the ribosome
3) transfer of information about the primary structure of the protein
4) rRNA
Answer
2. Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1) rRNA
2) formation in complex with proteins of the body of the ribosome
3) storage and transmission of hereditary information
4) uracil
5) tRNA
6) amino acid
8) mRNA synthesis
Answer
Choose one, the most correct option. Molecules are classified as biological polymers.
1) ribose
2) glucose
3) amino acids
Answer
Choose one, the most correct option. The bond that occurs between the nitrogenous bases of two complementary DNA strands
1) ionic
2) peptide
3) hydrogen
4) covalent polar
Answer
Choose one, the most correct option. The connection of two strands in a DNA molecule occurs due to
1) hydrophobic interactions of nucleotides
2) peptide bonds between nitrogenous bases
3) interactions of complementary nitrogenous bases
4) ionic interactions of nucleotides
Answer
How many nucleotides with cytosine does a DNA molecule contain if the number of nucleotides with thymine is 120, which is 15% of the total? Write down the corresponding number in your answer.
Answer
In RNA, nucleotides with uracil and adenine account for 10% each. Determine the percentage of nucleotides with thymine included in the complementary, double-stranded DNA chain. Write down only the appropriate number in your answer.
Answer
The section of the DNA chain of the bacteriophage lambda contains 23 nucleotides with thymine, how many nucleotides with cytosine in this section, if its length is 100 nucleotides? In response, write down only the number of nucleotides.
Answer
The mRNA molecule contains 200 nucleotides with uracil, which is 10% of the total number of nucleotides. How many nucleotides (in%) with adenine does one of the strands of the DNA molecule contain? Write down the corresponding number in your answer.
Answer
A fragment of a DNA molecule contains 60 nucleotides. Of these, 12 nucleotides are thymine. How many guanine nucleotides are in this fragment? Write only the number in your answer.
Answer
Establish a correspondence between the feature of a nucleic acid and its type: 1) i-RNA, 2) t-RNA. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) has the shape of a cloverleaf
B) delivers amino acids to the ribosome
C) has the smallest size of nucleic acids
D) serves as a matrix for protein synthesis
D) transfers hereditary information from the nucleus to the ribosome
Answer
Establish a correspondence between the characteristics and organic substances of the cell: 1) mRNA, 2) tRNA, 3) rRNA. Write down the numbers 1-3 in the order corresponding to the letters.
A) delivers amino acids for translation
B) contains information about the primary structure of the polypeptide
B) is part of the ribosome
D) serves as a matrix for translation
D) activates an amino acid
Answer
1. All of the features listed below, except for two, can be used to describe an RNA molecule. Identify two signs that “fall out” from the general list, and write down the numbers under which they are indicated.
1) consists of two polynucleotide chains twisted into a spiral
2) consists of one polynucleotide non-coiled chain
3) transfers hereditary information from the nucleus to the ribosome
4) has the largest size of nucleic acids
5) consists of AUHC nucleotides
Answer
2. All of the features listed below, except for two, can be used to describe the RNA molecule. Identify two signs that “fall out” from the general list, and write down the numbers under which they are indicated.
1) consists of two polynucleotide chains twisted into a spiral
2) transfers information to the site of protein synthesis
3) in complex with proteins builds the body of the ribosome
4) capable of self-doubling
5) transports amino acids to the site of protein synthesis
Answer
Choose one, the most correct option. A copy of one or a group of genes that carry information about the structure of proteins that perform one function is a molecule
2) tRNA
3) ATP
4) mRNA
Answer
A section of one of the two strands of a DNA molecule contains 300 nucleotides with adenine (A), 100 nucleotides with thymine (T), 150 nucleotides with guanine (G) and 200 nucleotides with cytosine (C). How many nucleotides are in two strands of DNA? Write your answer as a number.
Answer
1. How many nucleotides does a fragment of a double-stranded DNA molecule contain, containing 14 nucleotides with adenine and 20 nucleotides with guanine? Write down only the appropriate number in your answer.
Answer
2. How many nucleotides does a fragment of a double-stranded DNA molecule include if it contains 16 nucleotides with thymine and 16 nucleotides with cytosine? Write down only the appropriate number in your answer.
Answer
All of the features listed below, except for two, are used to describe the diagram of the structure of an organic substance molecule shown in the figure. Identify two signs that “fall out” from the general list, and write down the numbers under which they are indicated.
Deoxyribonucleic acids (DNA), high-polymer natural compounds contained in the nuclei of cells of living organisms; Together with proteins, histones form the substance of chromosomes. DNA is the carrier of genetic information, its individual sections correspond to certain genes. The DNA molecule consists of 2 polynucleotide chains twisted one around the other in a helix. Chains are built from a large number of monomers of 4 types - nucleotides, the specificity of which is determined by one of the 4 nitrogenous bases (adenine, guanine, cytosine, thymine). The combinations of three adjacent nucleotides in the DNA chain (triplets, or codons) make up the genetic code. Violations of the nucleotide sequence in the DNA chain lead to hereditary changes in the body - mutations. DNA is accurately reproduced during cell division, which ensures the transmission of hereditary traits and specific forms of metabolism in a number of generations of cells and organisms.
Deoxyribonucleic acids (DNA), nucleic acids containing deoxyribose as a carbohydrate component. DNA is the main component of the chromosomes of all living organisms; it represents the genes of all pro- and eukaryotes, as well as the genomes of many viruses. In the nucleotide sequence of DNA, genetic information is recorded (encoded) about all the features of the species and the characteristics of the individual (individual) - its genotype. DNA regulates the biosynthesis of components of cells and tissues, determines the activity of the organism throughout its life.
History of the discovery and study of DNA
Already in the middle of the 19th century, it was established that the ability to inherit certain characteristics of organisms is associated with the material contained in the cell nucleus. In 1868-72. Swiss biochemist I.F. Misher isolated a substance from pus cells (leukocytes) and salmon sperm, which he called nuclein, and later called deoxyribonucleic acid.
At the end of the 19th - beginning of the 20th centuries. thanks to the work of L. Kessel, P. Levene, E. Fisher and others, it was found that DNA molecules are linear polymer chains consisting of many thousands of monomers connected to each other - deoxyribonucleotides of four types. These nucleotides are formed by the residues of the five-carbon sugar deoxyribose, phosphoric acid, and one of the four nitrogenous bases: purines - adenine and guanine, and pyrimidines - cytosine and thymine. To designate bases, they began to use the initial letters of their names in English or Russian (in the Russian-language scientific literature) language: A, G (G), C (C) and T, respectively.
For a long time it was believed that DNA is found only in animal cells, until in the 1930s. Russian biochemist A. N. Belozersky did not show that DNA is an essential component of all living cells. The first evidence of the genetic role of DNA (as the substance of heredity) was obtained in 1944 by a group of American scientists (O. Avery and others), who, in experiments on bacteria, unambiguously established that with its help an inherited trait can be transferred from one cell to another.
By the middle of the 20th century the work of English scientists (A. Todd and others) finally elucidated the structure of nucleotides, which serve as monomeric links in the DNA molecule, and the type of internucleotide bond. All nucleotides are interconnected by a 3"-, 5"-phosphodiester bond in such a way that the phosphoric acid residue serves as a link between the 3"-carbon atom of deoxyribose of one nucleotide and the 5"-carbon atom of deoxyribose of another nucleotide. Based on this, the 3' end and the 5' end of the molecule are isolated in each DNA strand.
Structure of DNA. Discovery of the "double helix"
In 1950, the American biochemist E. Chargaff discovered significant differences in the nucleotide composition of DNA from different sources. In addition, it turned out that the composition of nucleotides in a DNA molecule obeys a number of patterns, the main of which are the equality of the total number of purine and pyrimidine bases and the equality of the amount of adenine and tinine (A-T) and guanine and cytosine (G-C). In 1953, the American biochemist J. Watson and the English physicist F. Crick, based on X-ray diffraction analysis of DNA crystals (M. Wilkins laboratory) and based on Chargaff's data, proposed a three-dimensional model of its structure. According to this model, DNA molecules are two right-handed polynucleotide chains around a common axis, or a double helix. There are approximately 10 nucleotide residues per turn of the helix. The strands in this double helix are anti-parallel, that is, they point in opposite directions, so that the 3" end of one strand is opposite the 5" end of the other.
The backbones of the chains are formed by deoxyribose residues and negatively charged phosphate groups. They are on the outside of the double helix (facing the surface of the molecule). The poorly water-soluble (hydrophobic) purine and pyrimidine bases of both chains are oriented inward and are located perpendicular to the axis of the double helix.
The antiparallel polynucleotide chains of the DNA double helix are not identical in either base sequence or nucleotide composition. However, they are complementary to each other: wherever adenine appears in one chain, thymine will definitely stand opposite it in the other chain, and cytosine of the other chain will definitely stand opposite guanine in one chain. This means that the sequence of bases in one chain uniquely determines the sequence of bases in the other (complementary) chain of the molecule. Moreover, these base pairs form hydrogen bonds with each other (three bonds are present in the G-C pair and two between A-T). Hydrogen bonds and hydrophobic interactions play a major role in the stabilization of the DNA double helix.
Heating, significant changes in pH, and a number of other factors cause the denaturation of the DNA molecule, leading to the separation of its chains. Under certain conditions, it is possible to completely restore the original (native) structure of the DNA molecule, its renaturation. The ability of complementary DNA chains to easily separate and then restore the original structure again underlies the self-reproduction of the DNA molecule, its replication (doubling): if two complementary DNA chains are divided, and then on each, as on a matrix, build new, strictly complementary chains, then the two newly formed molecules will be identical to the original. The discovery of this principle made it possible to explain the phenomenon of heredity at the molecular level.
Similarities and differences in the structure of natural DNA. Dimensions
Almost all natural DNA consists of two strands (with the exception of the single-stranded DNA of some viruses). In this case, DNA can be linear or circular (when the ends of the molecule are covalently closed). In prokaryotic cells, DNA is organized into one chromosome (nucleoid) and is represented by one circular macromolecule with a molecular weight of more than 10. In addition, some bacteria have one or more plasmids - small circular DNA molecules that are not associated with the chromosome. In eukaryotes, the bulk of DNA is located in the nucleus of the cell as part of the chromosomes (nuclear DNA). In each eukaryotic chromosome there is only one linear DNA molecule, but since in all eukaryotic cells (except sex) there is a double set of homologous chromosomes, then DNA is represented by two non-identical copies received by the body from the father and mother during the fusion of germ cells. The molecular weight of eukaryotic DNA is higher than that of prokaryotes (for example, in one of the chromosomes of the Drosophila fruit fly, it reaches 7.9 x 1010). In addition, the composition of mitochondria and chloroplasts includes circular DNA molecules with a molecular weight of 106-107. The DNA of these organelles is called cytoplasmic; it makes up approximately 0.1% of all cellular DNA.
The sizes of DNA molecules are usually expressed by the number of nucleotides that form them. These sizes vary from several thousand base pairs in bacterial plasmids and some viruses to many hundreds of thousands of base pairs in higher organisms. Such giant molecules must be packed extremely compactly in cells and viruses. For example, the length of the DNA nucleotide of Escherichia coli, consisting of approximately four million base pairs, is 1.4 mm, which is 700 times the size of the bacterial cell itself. The total length of all DNA in one single human cell is approximately 2 m. If we take into account that the adult human body consists of approximately 1013 cells, then the total length of all human DNA should be about 2x1013 m, or 2x1010 km (for comparison: the circumference of the globe - 4x104 km, and the distance from the Earth to the Sun - 1.44x108 km). How does the packaging of giant DNA molecules occur in a small volume of a cell or virus? The DNA double helix is not absolutely rigid, which makes it possible to form kinks, loops, supercoil structures, etc. In the bacterial nucleoid, this folding is supported by a small number of special proteins and, possibly, ribonucleic acids. In eukaryotic cells, with the help of a universal set of basic histone proteins and some non-histone proteins, DNA is converted into a very compact formation - chromatin, which is the main component of chromosomes. For example, the length of the DNA of the largest human chromosome is 8 cm, and in the composition of the chromosome, due to packaging, it does not exceed 8 nm.
Separate sections of DNA encoding the primary structure of a protein (polypeptide) and RNA are called genes. Hereditary information is recorded in a linear sequence of nucleotides. In different organisms, it is strictly individual and serves as the most important characteristic that distinguishes one DNA molecule from another and, accordingly, one gene from another. Animals of different species differ from each other because the DNA molecules of their cells have different nucleotide sequences, that is, they carry different information.
DNA biosynthesis
DNA biosynthesis occurs through replication, which ensures the exact copying of genetic information and its transmission from generation to generation. This process occurs with the participation of the enzyme DNA polymerase. A single-stranded (single-stranded) ribonucleic acid (RNA) molecule can also serve as a template for DNA synthesis, which occurs, for example, when cells are infected with retroviruses (including the AIDS virus). The life cycle of these viruses includes a reverse flow of information - from RNA to DNA. In this case, complementary copying of RNA into DNA is carried out using the reverse transcriptase enzyme. During the life of organisms, their DNA under the influence of external factors can undergo various damages (mutations) associated with a violation of the structure of nitrogenous bases. In the course of evolution, cells have developed protective mechanisms that ensure the restoration of its original structure - DNA repair.
Efficient methods have been developed for determining the nucleotide sequence in DNA molecules, thanks to which vast information has been accumulated about its primary structure in the genes of many viruses, some mitochondria and chloroplasts, as well as individual genes and fragments of large genomes. The nucleotide sequence of DNA of yeast, nematode worm (150 million base pairs) has been completely determined. Within the framework of the international program "Human Genome", the establishment of the nucleotide sequence of all DNA in the human genome (3 billion base pairs) has been basically completed.
Knowing the sequence of nucleotide alternation in a DNA molecule is important in the analysis of human hereditary diseases, in the isolation of individual genes and other functionally important DNA sections; it allows, using the genetic code, to unmistakably establish the primary structure of proteins encoded by certain genes. Information about the primary structure of DNA is widely used in genetic engineering to create recombinant DNA - molecules with desired properties, including DNA components from different organisms.
Molecular biology is one of the most important branches of biological sciences and involves a detailed study of the cells of living organisms and their components. The scope of her research includes many vital processes, such as birth, respiration, growth, death.
The invaluable discovery of molecular biology was the deciphering of the genetic code of higher beings and the determination of the cell's ability to store and transmit genetic information. The main role in these processes belongs to nucleic acids, which are distinguished in nature by two types - DNA and RNA. What are these macromolecules? What are they made of and what biological functions do they perform?
What is DNA?
DNA stands for deoxyribonucleic acid. It is one of the three macromolecules of the cell (the other two are proteins and ribonucleic acid), which ensures the preservation and transmission of the genetic code of the development and activity of organisms. Simply put, DNA is the carrier of genetic information. It contains the genotype of an individual, which has the ability to reproduce itself and transmits information by inheritance.
As a chemical substance, acid was isolated from cells as early as the 1860s, but until the middle of the 20th century, no one assumed that it was capable of storing and transmitting information. 
For a long time it was believed that these functions are performed by proteins, but in 1953 a group of biologists was able to significantly expand the understanding of the essence of the molecule and prove the primary role of DNA in the preservation and transmission of the genotype. The discovery was the discovery of the century, and scientists received the Nobel Prize for their work.
What is DNA made of?
DNA is the largest of biological molecules and consists of four nucleotides, consisting of a phosphoric acid residue. Structurally, the acid is quite complex. Its nucleotides are interconnected by long chains, which are combined in pairs into secondary structures - double helixes.
DNA tends to be damaged by radiation or various oxidizing substances, due to which a mutation process occurs in the molecule. The functioning of an acid directly depends on its interaction with another molecule - proteins. Interacting with them in the cell, it forms the substance chromatin, within which information is realized.
What is RNA?
RNA is a ribonucleic acid containing nitrogenous bases and phosphoric acid residues. 
There is a hypothesis that it is the first molecule that acquired the ability to reproduce itself in the era of the formation of our planet - in prebiological systems. RNA is still included in the genomes of individual viruses, performing in them the role that DNA plays in higher beings.
Ribonucleic acid consists of 4 nucleotides, but instead of a double helix, as in DNA, its chains are connected by a single curve. Nucleotides contain ribose, which is actively involved in metabolism. Depending on the ability to encode a protein, RNA is divided into matrix and non-coding.
The first acts as a kind of intermediary in the transfer of encoded information to ribosomes. The latter cannot code for proteins, but have other capabilities - translation and ligation of molecules.
How is DNA different from RNA?
In their chemical composition, acids are very similar to each other. Both are linear polymers and are an N-glycoside created from five-carbon sugar residues. The difference between them is that the sugar residue of RNA is ribose, a monosaccharide from the pentose group, which is easily soluble in water. The sugar residue of DNA is deoxyribose, or a derivative of ribose, which has a slightly different structure. 
Unlike ribose, which forms a ring of 4 carbon atoms and 1 oxygen atom, in deoxyribose the second carbon atom is replaced by hydrogen. Another difference between DNA and RNA is their size - larger. In addition, among the four nucleotides that make up DNA, one is a nitrogenous base called thymine, while in RNA, instead of thymine, its variant, uracil, is present.
