home » Hats » Nucleic acids as natural polymers. Biopolymers

Nucleic acids as natural polymers. Biopolymers

Polymers are high-molecular compounds consisting of many repeating atomic groups of different or identical structures - units. These links are interconnected by coordination or chemical bonds into branched or long linear chains and into three-dimensional spatial structures.

Polymers are:

synthetic,
artificial,
organic.

Organic polymers are formed in nature in animal and plant organisms. The most important of them are proteins, polysaccharides, nucleic acids, rubber and other natural compounds.

Man has long and widely used organic polymers in his daily life. Leather, wool, cotton, silk, fur - all this is used to produce clothing. Lime, cement, clay, organic glass (plexiglass) - in construction.

Organic polymers are also present in humans. For example, nucleic acids (also called DNA), as well as ribonucleic acids (RNA).

Properties of organic polymers

All organic polymers have special mechanical properties:

low fragility of crystalline and glassy polymers (organic glass, plastics);
elasticity, that is, high reversible deformation under small loads (rubber);
orientation of macromolecules under the influence of a directed mechanical field (production of films and fibers);
at low concentrations, the viscosity of solutions is high (polymers first swell and then dissolve);
under the influence of a small amount of reagent they can quickly change their physical and mechanical characteristics (for example, leather tanning, rubber vulcanization).

Table 1. Combustion characteristics of some polymers.

Polymers	Behavior of the material when introduced into the flame and flammability	Character of the flame	Smell
Polyethylene (PE)	It melts drop by drop, burns well, and continues to burn when removed from the flame.	Luminous, initially bluish, then yellow	Burning paraffin
Polypropylene (PP)	Same	Same	Same
Polycarbonate (PC)	Same	Smoking
Polyamide (PA)	Burns, flows like a thread	Bluish below, with yellow edges	Singed hair or burnt plants
Polyurethane (PU)	Burns, flows drop by drop	Yellow, bluish below, glowing, gray smoke	Harsh, unpleasant
Polystyrene (PS)	Self-ignites, melts	Bright yellow, glowing, smoky	Sweetish floral, with a hint of styrene scent
Polyethylene terephthalate (PET)	Burning, dripping	Yellow-orange, smoky	Sweet, fragrant
Epoxy resin (ED)	Burns well, continues to burn when removed from flame	Yellow smoky	Specific fresh (at the very beginning of heating)
Polyester resin (PN)	Burns, charred	Glowing, smoky, yellow	Sweetish
Rigid polyvinyl chloride (PVC)	Burns with difficulty and scattering, when removed from the flame it goes out and softens	Bright green	Acute, hydrogen chloride
PVC plasticized	Burns with difficulty and when removed from the flame, with scattering	Bright green	Acute, hydrogen chloride
Phenol-formaldehyde resin (FFR)	Difficult to light, burns poorly, retains its shape	Yellow	Phenol, formaldehyde

Table 2. Solubility of polymer materials.

Table 3. Coloring of polymers according to the Lieberman-Storch-Moravsky reaction.

Articles on the topic

Among most materials, the most popular and widely known are polymer composite materials (PCMs). They are actively used in almost every area of human activity. It is these materials that are the main component for the manufacture of various products used for completely different purposes, from fishing rods and boat hulls, to cylinders for storing and transporting flammable substances, as well as helicopter rotor blades. Such wide popularity of PCM is associated with the ability to solve technological problems of any complexity associated with the production of composites with certain properties, thanks to the development of polymer chemistry and methods for studying the structure and morphology of polymer matrices that are used in the production of PCM.

Presentation on the topic: Higher natural polymers - Proteins and Nucleic acids

1 of 25

Presentation on the topic:

Slide no. 1

Slide description:

Slide no. 2

Slide description:

Purpose of the lesson: To consolidate and deepen students’ understanding of natural polymers using the example of proteins and nucleic acids. Systematize knowledge about the composition, structure, properties and function of proteins. Have an idea of the chemical and biological synthesis of proteins, the creation of artificial and synthetic food. Expand your understanding of the composition and structure of nucleic acids. Be able to explain the construction of the DNA double helix based on the principle of complementarity. Know the role of nucleic acids in the life of organisms. Continue to develop self-education skills, the ability to listen to a lecture, and highlight the main thing. Take notes on the preparation of the plan or theses. To develop the cognitive interest of students, to establish interdisciplinary connections (with biology).

Slide no. 3

Slide description:

Slide no. 4

Slide description:

Slide no. 5

Slide description:

Values of proteins Organisms living on Earth today contain about a thousand billion tons of proteins. Distinguished by the inexhaustible variety of structure, which at the same time is strictly specific to each of them, proteins, together with nucleic acids, create the material basis for the existence of the entire wealth of organisms in the world around us. Proteins are characterized by the ability for intramolecular interactions, which is why the structure of protein molecules is so dynamic and changeable. Proteins interact with a wide variety of substances. By combining with each other or with nucleic acids, polysaccharides and lipids, they form ribosomes, mitochondria, lysosomes, membranes of the endoplasmic reticulum and other subcellular structures in which a variety of metabolic processes are carried out. Therefore, it is proteins that play an outstanding role in the phenomena of life.

Slide no. 6

Slide description:

Levels of organization of protein molecules Primary Secondary Tertiary Quaternary One of the difficult tasks of protein chemistry was deciphering the sequence of amino acid residues in the polypeptide chain, i.e., the primary structure of the protein molecule. It was first solved by the English scientist F. Sanger and his colleagues in 1945-1956. They established the primary structure of the hormone insulin, a protein produced by the pancreas. For this, F. Sanger was awarded the Nobel Prize in 1958.

Slide no. 7

Slide description:

Slide no. 8

Slide description:

Slide no. 9

Slide description:

Slide no. 10

Slide description:

Chemical properties of proteins (video film) A characteristic reaction of proteins is denaturation: Coagulation of proteins when heated. Precipitation of proteins with concentrated alcohol. Precipitation of proteins with salts of heavy metals. 2. Color reactions of proteins: Xanthoprotein reaction Biuret reaction Determination of sulfur content in the composition of a protein molecule.

Slide no. 11

Slide description:

The role of proteins in vital processes It is of great interest to study not only the structure, but also the role of proteins in vital processes. Many of them have protective (immunoglobulins) and toxic (snake venoms, cholera, diphtheria and tetanus toxins, enterotoxin. B from staphylococcus, butulism toxin) properties important for medical purposes. But the main thing is that proteins constitute the most important and irreplaceable part of human food. Nowadays, 10-15% of the world's population are hungry, and 40% receive junk food with insufficient protein content. Therefore, humanity is forced to industrially produce protein - the most scarce product on Earth. This problem is intensively solved in three ways: the production of feed yeast, the preparation of protein-vitamin concentrates based on petroleum hydrocarbons in factories, and the isolation of proteins from non-food raw materials of plant origin. In our country, protein-vitamin concentrate is produced from hydrocarbon raw materials. Industrial production of essential amino acids is also promising as a protein substitute. Knowledge of the structure and functions of proteins brings humanity closer to mastering the innermost secret of the phenomenon of life itself.

Slide no. 12

Slide description:

NUCLEIC ACIDS Nucleic acids are natural high-molecular organic compounds, polynucleotides, that provide storage and transmission of hereditary (genetic) information in living organisms. Nucleic acids were discovered in 1869 by the Swiss scientist F. Miescher as an integral part of cell nuclei, so they got their name from the Latin word nucleus - core. Nycleus - nucleus. For the first time, DNA and RNA were extracted from the cell nucleus. That's why they are called nucleic acids. The structure and functions of nucleic acids were studied by the American biologist J. Watson and the English physicist F. Crick.

Slide no. 13

Slide description:

In 1953, the American biochemist J. Watson and the English physicist F. Crick built a model of the spatial structure of DNA; which looks like a double helix. It corresponded to the data of the English scientists R. Franklin and M. Wilkins, who, using X-ray diffraction analysis of DNA, were able to determine the general parameters of the helix, its diameter and the distance between the turns. In 1962, Watson, Crick and Wilkins were awarded the Nobel Prize for this important discovery.

Slide no. 14

Slide description:

Slide no. 15

Slide description:

Structure of nucleic acids There are three types of nucleic acids: DNA (deoxyribonucleic acids), RNA (ribonucleic acids) and ATP (adenosine triphosphate). Like carbohydrates and proteins, they are polymers. Like proteins, nucleic acids are linear polymers. However, their monomers - nucleotides - are complex substances, in contrast to fairly simple sugars and amino acids.

Slide no. 16

Slide description:

Comparative characteristics of the DNA and RNA DNAILOLOGICAL POLIMERMONOMER - Nucleotide4 type of nitrogenous bases: adenine, thyamin, guanine, cytosin. Continual pairs: adenine -type, guanine -cytosinee - nucleus - the storage of hereditary information ishar - deoxiribosis of the RNKBiological polymermonomer - nucleotide - nucleotide 4 Azo Tysty foundations: adenin, guanine , cytosine, uracil Complementary pairs: adenine-uracil, guanine-cytosine Location - nucleus, cytoplasm Functions - transfer, transmission of hereditary information. Sugar - ribose Description of the slide:

Slide no. 23

Slide description:

Application of NK Throughout life, a person gets sick, finds himself in unfavorable production or climatic conditions. The consequence of this is an increase in the frequency of “failures” in the well-functioning genetic apparatus. Until a certain time, “failures” do not manifest themselves outwardly, and we do not notice them. Alas! Over time, changes become obvious. First of all, they appear on the skin. Currently, the results of research on biomacromolecules are emerging from the walls of laboratories, beginning to increasingly help doctors and cosmetologists in their daily work. Back in the 1960s. It became known that isolated DNA strands cause cell regeneration. But only in the very last years of the 20th century it became possible to use this property to restore aging skin cells.

Slide no. 24

Slide description:

Application of NC Science is still far from the possibility of using exogenous DNA strands (with the exception of viral DNA) as a template for “new” DNA synthesis directly in human, animal or plant cells. The fact is that the host cell is reliably protected from the introduction of foreign DNA by specific enzymes present in it - nucleases. Foreign DNA will inevitably undergo destruction, or restriction, under the action of nucleases. DNA will be recognized as “foreign” by the absence of a pattern of distribution of methylated bases inherent in the DNA of the host cell that is specific to each organism. At the same time, the closer the cells are related, the more their DNA will form hybrids. The result of this research is various cosmetic creams that include “magic threads” for skin rejuvenation.

Slide no. 25

Slide description:

Reinforcement of the lesson (test control) Option 11. A double polynucleotide chain is characteristic of molecules: a) DNA b) RNAc) both previous answers are correct.2. Average molecular weight, which type of nucleic acid is larger? a) DNA b) RNA c) depends on the type of living cell3. What substances are not an integral part of the nucleotide? a) pyrimidine or purine base. b) ribose and deoxyribose c) α - amino acids d) phosphoric acid 4. DNA nucleotides do not contain the following residues as bases: a) cytosine b) guanine b) uracil d) adenine e) thymine5. The nucleotide sequence is the structure of nucleic acids: a) primary b) tertiaryb) secondary d) quaternary 2 option1. Nucleic acids get their name from the Latin word: a) nucleus c) life b) cell d) first2. Polymer chain, which nucleic acid is a sequence of nucleotides?a) DNA b) RNA c) both types of nucleic acids3. The secondary structure in the form of a double helix is characteristic of the molecules: a) DNA c) RNAb) proteins d) all nucleic acids4. A purine base is not: a) adenine c) guanine b) thymine d) all are5. A nucleotide molecule does not contain: a) a monosaccharide residue b) a nitrogenous base residue b) an amino acid residue d) a phosphoric acid residue

A special, very important group of natural chemical substances consists of high molecular weight compounds (polymers). They can be divided into two large groups:

Natural organic polymers - biopolymers

Natural inorganic polymers

First, let's look at substances related to biopolymers.

The mass of biopolymer molecules reaches several tens of thousands and the role of these compounds is enormous. Polymer substances are the basis of Life on Earth.

Table 1

Organic natural polymers – biopolymers– provide vital processes for all animal and plant organisms. It is interesting that out of the many possible options, Nature “selected” only 4 types of polymers:

Picture 1

Polysaccharides

Polysaccharides are natural high-molecular carbohydrates, the macromolecules of which consist of monosaccharide residues.

Polysaccharides make up the bulk of organic matter in the Earth's biosphere. In living nature, they perform important biological functions, acting as:

structural components of cells and tissues,

energy reserve,

protective substances.

Polysaccharides are formed from low molecular weight compounds of the general formula C n H 2 n O n called sugars or carbohydrates. Sugars are characterized by the presence of aldehyde or ketone groups; accordingly, the former are called aldoses, the latter - ketoses. Among the sugars with n = 6, called hexoses, there are 16 isomeric aldohexoses and 16 ketohexoses. However, only four of them (α-galactose, d-mannose, d-glucose, d-fructose) are found in living cells. The biological role of sugars is determined by the fact that they are a source of energy needed by the body, which is released during their oxidation, and the starting material for the synthesis of macromolecules.

In the latter case, the ability of sugars to form cyclic structures is of great importance, as illustrated below using the example of glucose and fructose:

Rice. 2

In aqueous solution, glucose contains 99.976% cyclic isomer. Ketohexoses have five-membered cyclic isomers. Cyclic molecules of monosaccharides can bond with each other to form so-called glycosidic bonds through the condensation of hydroxyl groups.

The most common are polysaccharides whose repeating units are residues of α-D-glucopyranose or its derivatives.

The main representatives of polysaccharides are starch And cellulose- built from the remains of one monosaccharide - glucose. Starch and cellulose have the same molecular formula:

(C6h10o5)n,

but absolutely various properties. This is explained by the peculiarities of their spatial structure.

Starch consists of α-glucose residues, and cellulose - from β-glucose, which are spatial isomers and differ only in the position of one hydroxyl group (highlighted):

Figure 3

Taking into account the spatial structure of the six-membered ring, the formulas of these isomers have the form:

Figure 4

The most important polysaccharides also include glycogen(C 6 H 10 O 5) n, formed in human and animal bodies as a result of biochemical transformations from plant carbohydrates. Like starch, glycogen consists of α-glucose residues and performs similar functions (hence why it is often called animal starch).

From chemical properties reactions of polysaccharides are most important hydrolysis And derivation due to reactions of macromolecules at OH groups.

Hydrolysis of polysaccharides occurs in dilute solutions of mineral acids (or under the action of enzymes). At the same time, in macromolecules the bonds connecting the monosaccharide units are broken - glycosidic bonds(similar to hydrolysis of disaccharides).

Complete hydrolysis of polysaccharides leads to the formation of monosaccharides (cellulose, starch and glycogen are hydrolyzed to glucose): (C6H10O5) + (C6H10O5) n (C6H10O5) H2O(H+)

C6H12O6

With incomplete hydrolysis, oligosaccharides are formed, including disaccharides. The ability of polysaccharides to hydrolyze increases in the following order:< крахмал < гликоген

cellulose

From cellulose (a waste product from the wood industry), ethanol (called “hydrolytic alcohol”) is produced through acid hydrolysis and subsequent fermentation of the resulting glucose.

Among polysaccharide derivatives, cellulose ethers and esters are of greatest practical importance. Their formation occurs in the reactions of cellulose macromolecules along alcohol OH groups (each monosaccharide unit has 3 OH groups): The most important cellulose derivatives include: - methylcellulose

(cellulose methyl ethers) of the general formula N ( X

- = 1, 2 or 3); cellulose acetate

- (cellulose triacetate) - ester of cellulose and acetic acid nitrocellulose

(cellulose methyl ethers) of the general formula N ((cellulose nitrates) - cellulose nitrates:

= 1, 2 or 3).

These polymer materials are used in the production of artificial fibers, plastics, films, paints and varnishes, smokeless powder, explosives, solid rocket fuels, etc.

Slide 1

Slide 3

Slide 4

Slide 5

Slide 6

Levels of organization of protein molecules Primary Secondary Tertiary Quaternary One of the difficult problems of protein chemistry was deciphering the sequence of amino acid residues in the polypeptide chain, i.e., the primary structure of the protein molecule. It was first solved by the English scientist F. Sanger and his colleagues in 1945-1956. They established the primary structure of the hormone insulin, a protein produced by the pancreas. For this, F. Sanger was awarded the Nobel Prize in 1958.

Slide 7

a specific sequence of a-amino acid residues in a polypeptide chain Primary structure -

Slide 8

Slide 9

Quaternary structure – aggregates of several protein macromolecules (protein complexes), formed through the interaction of different polypeptide chains

Slide 10

Chemical properties of proteins (video film) A characteristic reaction of proteins is denaturation: Coagulation of proteins when heated. Precipitation of proteins with concentrated alcohol. Precipitation of proteins by salts of heavy metals. 2. Color reactions of proteins: Xanthoprotein reaction Biuret reaction Determination of sulfur content in the composition of a protein molecule.

Slide 11

Slide 12

NUCLEIC ACIDS Nucleic acids are natural high-molecular organic compounds, polynucleotides, that ensure the storage and transmission of hereditary (genetic) information in living organisms. Nucleic acids were discovered in 1869 by the Swiss scientist F. Miescher as an integral part of cell nuclei, so they got their name from the Latin word nucleus - nucleus. Nycleus" - core. For the first time, DNA and RNA were extracted from the cell nucleus. That's why they are called nucleic acids. The structure and functions of nucleic acids were studied by the American biologist J. Watson and the English physicist F. Crick.

Slide 13

STRUCTURES OF DNA AND RNA In 1953, the American biochemist J. Watson and the English physicist F. Crick built a model of the spatial structure of DNA; which looks like a double helix. It corresponded to the data of the English scientists R. Franklin and M. Wilkins, who, using X-ray diffraction analysis of DNA, were able to determine the general parameters of the helix, its diameter and the distance between the turns. In 1962, Watson, Crick and Wilkins were awarded the Nobel Prize for this important discovery.

Slide 14

NUCLEIC ACIDS MONOMERS - NUCLEOTIDES DNA - deoxyribonucleic acid RNA ribonucleic acid Composition of the nucleotide in DNA Composition of the nucleotide in RNA Nitrogenous bases: Adenine (A) Guanine (G) Cytosine (C) Uracil (U): Ribose Phosphoric acid residue Nitrogenous bases: Adenine (A ) Guanine (G) Cytosine (C) Thymine (T) Deoxyribose Phosphoric acid residue Messenger RNA (i-RNA) Transfer RNA (t-RNA) Ribosomal RNA (r-RNA)

Slide 15

There are three types of nucleic acids: DNA (deoxyribonucleic acids), RNA (ribonucleic acids) and ATP (adenosine triphosphate). Like carbohydrates and proteins, they are polymers. Like proteins, nucleic acids are linear polymers. However, their monomers - nucleotides - are complex substances, in contrast to fairly simple sugars and amino acids. Structure of nucleic acids

Slide 16

Comparative characteristics of DNA and RNA DNA Biological polymer Monomer - nucleotide 4 types of nitrogenous bases: adenine, thymine, guanine, cytosine. Complementary pairs: adenine-thymine, guanine-cytosine Location - nucleus Functions - storage of hereditary information Sugar - deoxyribose RNA Biological polymer Monomer - nucleotide 4 types of nitrogenous bases: adenine, guanine, cytosine, uracil Complementary pairs: adenine-uracil, guanine-cytosine Location – nucleus, cytoplasm Functions – transfer, transmission of hereditary information. Sugar - ribose

Slide 17

Triplet A triplet is three consecutive nucleotides. The sequence of triplets determines the sequence of amino acids in a protein! Triplets located one behind the other, determining the structure of one protein molecule, represent a GENE.

Slide 18

Replication is the process of self-duplication of a DNA molecule based on the principle of complementarity. The meaning of replication: due to the self-duplication of DNA, cell division processes occur.

Slide 19

Between the nitrogen bases of the pair A and T, 2 hydrogen bonds are formed, and between G and C - 3, therefore the strength of the G-C bond is higher than A-T: Complementary pairs

Slide 20

Slide 21

Slide 22

The meaning of nucleic acids Storage, transfer and inheritance of information about the structure of protein molecules. The stability of NK is the most important condition for the normal functioning of cells and entire organisms. A change in the structure of the NK is a change in the structure of cells or physiological processes - a change in life activity.

Slide 23

Slide 24

Application of NC Science is still far from the possibility of using exogenous DNA strands (with the exception of viral DNA) as a template for “new” DNA synthesis directly in human, animal or plant cells. The fact is that the host cell is reliably protected from the introduction of foreign DNA by specific enzymes present in it - nucleases. Foreign DNA will inevitably undergo destruction, or restriction, under the action of nucleases. DNA will be recognized as “foreign” by the absence of a pattern of distribution of methylated bases inherent in the DNA of the host cell that is specific to each organism. At the same time, the closer the cells are related, the more their DNA will form hybrids. The result of this research is various cosmetic creams containing “magic threads” for skin rejuvenation.

Slide 25

Reinforcement of the lesson (test control) Option 1 1. A double polynucleotide chain is characteristic of molecules: a) DNA b) RNA c) both previous answers are correct. 2. Average molecular weight, which type of nucleic acid is larger? a) DNA b) RNA c) depends on the type of living cell 3. What substances are not an integral part of the nucleotide? a) pyrimidine or purine base. b) ribose and deoxyribose c) α - amino acids d) phosphoric acid 4. DNA nucleotides do not contain residues as bases: a) cytosine c) guanine b) uracil d) adenine e) thymine 5. The sequence of nucleotides is the structure of nucleic acids: a) primary c) tertiary b) secondary d) quaternary Option 2 1. Nucleic acids get their name from the Latin word: a) nucleus c) life b) cell d) first 2. Polymer chain, which nucleic acid is a sequence of nucleotides ? a) DNA b) RNA c) both types of nucleic acids 3. The secondary structure in the form of a double helix is characteristic of the molecules: a) DNA c) RNA b) proteins d) all nucleic acids 4. A purine base is not: a) adenine c) guanine b) thymine d) all are 5. A nucleotide molecule does not contain: a) a monosaccharide residue c) a nitrogenous base residue b) an amino acid residue d) a phosphoric acid residue

Nucleic acids are natural organic high-molecular organic compounds that ensure the storage and transmission of hereditary (genetic) information in living organisms.

Nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). They were discovered in 1869 by F. Miescher in the nuclei of leukocytes and called nucleic acids, because. core - nucleus (nucleus).

Biopolymer, the monomer of which is nucleotide. DNA is a polynucleotide with a very large molecular weight. One molecule can contain 10 8 or more nucleotides. The nucleotide contains a five-atom sugar, deoxyribose, a phosphoric acid residue, and one nitrogenous base. There are only four nitrogenous bases - adenine (A), guanine (G), cytosine (C) and thymine (T). Thus, there are only four nucleotides: adenine, guanine, cytosine and thymine (Fig. 10).

Rice. 10. DNA structure diagram Fig. 11. Structure of a section of a DNA molecule

The order of alternation of nucleotides in DNA is different in different organisms.

In 1953, D. Watson and F. Crick built a spatial model of DNA. Two experimental advances contributed to this discovery:

1) Chargaff obtained pure DNA samples and analyzed the number of bases in each sample. It turned out that no matter what organism the DNA was isolated from, the amount of adenine is equal to the amount of thymine ( A = T), and the amount of guanine is equal to the amount of cytosine ( G = C);

2) Wilkins and Franklin used X-ray diffraction to obtain a good picture of DNA (Fig. 12).

The DNA molecule consists of two chains connected to each other and resembles a rope ladder (Fig. 11). The sides of the stairs are twisted like electrical wires. The sides are alternating sugar and phosphoric acid. The rungs of this ladder are nitrogenous bases connected according to the principle of complementarity (A = T; G = C). There is a double hydrogen bond between adenine and thymine, and a triple hydrogen bond between guanine and cytosine.

Rice. 13 Nucleotide structure

The width of the double helix is 1.7 nm, one turn contains 10 base pairs, the length of the turn is 3.4 nm, the distance between nucleotides is 0.34 nm. When combined with certain proteins—histones—the degree of helicalization of the molecule increases. The molecule thickens and shortens. Subsequently, spiralization reaches a maximum, and a spiral of an even higher level arises - a superspiral. In this case, the molecule becomes visible in a light microscope as an elongated, well-stained body - chromosome.

DNA synthesis

DNA is part of chromosomes (the complex of DNA with the histone protein makes up 90% of the chromosome. The question arises, why after cell division the number of chromosomes does not decrease, but remains the same. Because before cell division, doubling occurs (synthesis) DNA, and, consequently, chromosome duplication. Under the influence of an enzyme nucleases hydrogen bonds between nitrogenous bases in a certain section of DNA are broken and the double strand of DNA begins to unwind, one strand moving away from the other. From free nucleotides that are found in the cell nucleus under the action of an enzyme DNA polymerases complementary strands are built. Each of the separated paired strands of the DNA molecule serves as a template for the formation of another complementary strand around it. Then each old (mother) and new (daughter) threads are twisted again in the form of a spiral. As a result, two new completely identical double helices are formed (Fig. 14).

The ability to reproduce is a very important feature of the DNA molecule.

Rice. 14. “Maternal” DNA serves as a template for the synthesis of complementary chains

Function of DNA in a cell

Deoxyribonucleic acid performs extremely important functions necessary for both the maintenance and reproduction of life.

Firstly , - This storage of hereditary information, which is contained in the nucleotide sequence of one of its chains. The smallest unit of genetic information after a nucleotide is three consecutive nucleotides - triplet. The sequence of triplets in a polynucleotide chain determines the sequence of amino acids in a protein molecule. Triplets located one after another, determining the structure of one polypeptide chain, are gene.

The second function of DNA is the transmission of hereditary information from generation to generation. It is carried out thanks to reduplication(doubling) of the mother molecule and subsequent distribution of daughter molecules between descendant cells. It is the double-stranded structure of DNA molecules that determines the possibility of the formation of absolutely identical daughter molecules during reduplication.

Finally, DNA is involved as a template in the process of transferring genetic information from the nucleus to the cytoplasm to the site of protein synthesis. In this case, on one of its chains, according to the principle of complementarity, a messenger RNA molecule is synthesized from the nucleotides of the environment surrounding the molecule.

RNA, just like DNA, is a biopolymer (polynucleotide), the monomers of which are nucleotides (Fig. 15). The nitrogenous bases of three nucleotides are the same as those that make up DNA (adenine, guanine, cytosine), the fourth - uracil– present in the RNA molecule instead of thymine. RNA nucleotides contain another pentose - ribose(instead of deoxyribose). Based on their structure, double-stranded and single-stranded RNA are distinguished. Double-stranded RNAs are the custodians of genetic information in a number of viruses, i.e. They perform the functions of chromosomes.

RNAs carry information about the sequence of amino acids in proteins, i.e. about the structure of proteins, from chromosomes to the place of their synthesis, and are involved in protein synthesis.

There are several types of single-stranded RNA. Their names are determined by their function and location in the cell. All types of RNA are synthesized on DNA, which serves as a template.

1. Transfer RNA(t-RNA) The smallest, it contains 76 - 85 nucleotides. It has the appearance of a clover leaf, at the long end of which there is a triplet of nucleotides (ANC), where the activated amino acid is added. At the short end there is a nitrogenous base - guanine, which prevents t-RNA from being destroyed. At the opposite end is an anticodon, which is strictly complementary to the genetic code on the messenger RNA. The main function of tRNA is the transfer of amino acids to the site of protein synthesis. Of the total RNA content in a cell, t-RNA accounts for 10%.

2. Ribosomal RNA(r-RNA) contained in ribosomes, consist of 3 - 5 thousand nucleotides. Of the total RNA content in a cell, r-RNA accounts for 90%.

3. Information (i-RNA) or matrix (m-RNA) . Contained in the nucleus and cytoplasm, messenger RNA molecules can consist of 300 - 30,000 nucleotides. Its function is to transfer information about the primary structure of the protein to ribosomes. The share of mRNA is 0.5 - 1% of the total RNA content of the cell.

Genetic code

Genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in DNA (Fig. 16).

Fig. 16 Genetic code

Properties of the genetic code

1. The code is triplet. This means that each amino acid is encrypted by a sequence of three nucleotides called triplet or codon. Thus, the amino acid cysteine corresponds to the triplet ACA, valine - CAA, lysine - TTT (Fig.).

2The code is degenerate. There are 64 genetic codes in total, while 20 amino acids are encoded; when they go to mRNA, protein synthesis stops. Each amino acid is encrypted by several genetic codes, with the exception of methionine and tryptophan. This code redundancy is of great importance for increasing the reliability of the transfer of genetic information. For example, the amino acid arginine can correspond to triplets HCA, HCT, HCC, etc. It is clear that a random replacement of the third nucleotide in these triplets will not affect the structure of the synthesized protein.

3. The code is universal. The genetic code is the same for all creatures living on Earth (humans, animals, plants, bacteria and fungi).

4. The genetic code is continuous. Nucleotides in DNA do not overlap each other; there are no spaces or punctuation marks between triplets (codons). How is a section of a DNA molecule that carries information about the structure of one protein delimited from other sections? There are triplets, whose function is to trigger the synthesis of a polynucleotide chain, and triplets ( UAA, UAG, UGA), which stop synthesis.

5. The genetic code is specific. There are no cases where the same geotriplet corresponds to more than one amino acid.

Protein biosynthesis in the cell

Protein biosynthesis in a cell consists of two stages:

1. Transcription.

2. Broadcast.

1. Transcription - This is the rewriting of information about the primary structure of a protein from a certain section of DNA (gene) to mRNA according to the principle of complementarity using the enzyme RNA polymerase.

Reading of hereditary information begins from a certain section of DNA, which is called promoter It is located in front of the gene and includes about 80 nucleotides. The enzyme RNA polymerase recognizes the promoter, binds firmly to it and melts it, separating the nucleotides of the complementary DNA chains, then this enzyme begins

move along the gene and as the DNA chains are separated, mRNA is synthesized on one of them, which is called the sense chain. The finished mRNA enters the cytoplasm through the pores of the nuclear membrane and penetrates the small subunit of the ribosome, and those parts of the gene where the polymerase formed the mRNA are again twisted into a spiral, the mRNA can penetrate several ribosomes at once and this complex is called polysome. In the cytoplasm, amino acids are activated by the enzyme aminoacyl-t-synthetase and attached to the long end of t-RNA (Fig. 17). 2. Translation is the translation of hereditary information from the language of nucleotides to the language of amino acids.

Translation begins with the start codon AUG, to which the methionine-loaded tRNA is attached with its anticodon UAC. The large subunit of the ribosome has aminoacyl and peptidyl centers. First, amino acid I (methionine) enters the aminoacyl center, and then, together with its tRNA, is mixed into the peptidyl center. The aminoacyl center is released and can accept the next tRNA with its amino acid. The second tRNA, loaded with the 2nd amino acid, enters the large subunit of the ribosome and, with its anticodon, connects with the complementary codon of the mRNA. Immediately, with the help of the enzyme peptidyl transferase, the preceding amino acid, with its carboxyl group (COOH), combines with the amino group (NH 2) of the newly arrived amino acid. A peptide bond (-CO-NH-) is formed between them. As a result, the t-RNA that brought methionine is released, and two amino acids (dipeptide) are added to the t-RNA at the aminoacyl center. For the further process of growth of the polypeptide chain, the aminoacyl center must be released. The large and small subunit of the ribosome scrolls relative to each other (like winding a clock), the triplet of nucleotides on the mRNA moves forward, and the next triplet of nucleotides takes its place. In accordance with the codonomy of the i-RNA, the next t-RNA brings an amino acid to the released aminoacyl center, which is connected to the previous one using a peptide bond, and the second t-RNA leaves the ribosome. Then the ribosome again moves one codon and the process repeats. The sequential addition of amino acids to the polypeptide chain occurs in strict accordance with the sequence of columns on the mRNA.

Views