Biopolymers- a class of polymers that occur naturally in nature and are part of living organisms: proteins, nucleic acids, polysaccharides. Biopolymers consist of identical (or different) units - monomers. Monomers of proteins are amino acids, nucleic acids are nucleotides, and in polysaccharides they are monosaccharides.

There are two types of biopolymers - regular (some polysaccharides) and irregular (proteins, nucleic acids, some polysaccharides).

Squirrels

Proteins have several levels of organization - primary, secondary, tertiary, and sometimes quaternary. The primary structure is determined by the sequence of monomers, the secondary structure is determined by intra- and intermolecular interactions between monomers, usually through hydrogen bonds. Tertiary structure depends on the interaction of secondary structures, quaternary, as a rule, is formed by combining several molecules with a tertiary structure.

The secondary structure of proteins is formed by the interaction of amino acids using hydrogen bonds and hydrophobic interactions. The main types of secondary structure are

α-helix, when hydrogen bonds occur between amino acids in the same chain,

β-sheets (folded layers), when hydrogen bonds are formed between different polypeptide chains running in different directions (antiparallel,

disordered areas

Computer programs are used to predict secondary structure.

Tertiary structure or "fold" is formed by the interaction of secondary structures and is stabilized by non-covalent, ionic, hydrogen bonds and hydrophobic interactions. Proteins that perform similar functions usually have similar tertiary structures. An example of a fold is a β-barrel, where the β-sheets are arranged in a circle. The tertiary structure of proteins is determined using X-ray diffraction analysis.

An important class of polymeric proteins are fibrillar proteins, the best known of which is collagen.

In the animal world, proteins usually act as supporting, structure-forming polymers. These polymers are built from 20 α-amino acids. Amino acid residues are linked into protein macromolecules by peptide bonds resulting from the reaction of carboxyl and amino groups.

The importance of proteins in living nature is difficult to overestimate. These are the building materials of living organisms, biocatalysts - enzymes that ensure reactions occur in cells, and enzymes that stimulate certain biochemical reactions, i.e. ensuring selectivity of biocatalysis. Our muscles, hair, skin are made of fibrous proteins. A blood protein that is part of hemoglobin promotes the absorption of oxygen in the air; another protein, insulin, is responsible for the breakdown of sugar in the body and, therefore, for providing it with energy. The molecular weight of proteins varies widely. Thus, insulin, the first protein whose structure was established by F. Sanger in 1953, contains about 60 amino acid units, and its molecular weight is only 12,000. To date, several thousand protein molecules have been identified, the molecular weight of some of them reaches 106 or more.

Nucleic acids

The primary structure of DNA is a linear sequence of nucleotides in a chain. As a rule, the sequence is written in the form of letters (for example, AGTCATGCCAG), and the recording is carried out from the 5" to the 3" end of the chain.

Secondary structure is a structure formed due to non-covalent interactions of nucleotides (mostly nitrogenous bases) with each other, stacking and hydrogen bonds. The DNA double helix is ​​a classic example of secondary structure. This is the most common form of DNA in nature, which consists of two anti-parallel complementary polynucleotide chains. Antiparallelism is realized due to the polarity of each of the circuits. Complementarity is understood as the correspondence of each nitrogenous base of one DNA chain to a strictly defined base of another chain (opposite A is T, and opposite G is C). DNA is held in a double helix by complementary base pairing - the formation of hydrogen bonds, two in the A-T pair and three in the G-C pair.

In 1868, the Swiss scientist Friedrich Miescher isolated a phosphorus-containing substance from cell nuclei, which he called nuclein. Later, this and similar substances were called nucleic acids. Their molecular weight can reach 109, but more often ranges from 105-106. The starting substances from which nucleotides are built - units of nucleic acid macromolecules are: carbohydrate, phosphoric acid, purine and pyrimidine bases. In one group of acids, ribose acts as a carbohydrate, in the other, deoxyribose.

In accordance with the nature of the carbohydrate they contain, nucleic acids are called ribonucleic and deoxyribonucleic acids. Common abbreviations are RNA and DNA. Nucleic acids play the most important role in life processes. With their help, two important tasks are solved: storage and transmission of hereditary information and matrix synthesis of macromolecules DNA, RNA and protein.

Polysaccharides

3-dimensional structure of cellulose

Polysaccharides synthesized by living organisms consist of a large number of monosaccharides connected by glycosidic bonds. Often polysaccharides are insoluble in water. These are usually very large, branched molecules. Examples of polysaccharides that are synthesized by living organisms are storage substances starch and glycogen, as well as structural polysaccharides - cellulose and chitin. Since biological polysaccharides consist of molecules of different lengths, the concepts of secondary and tertiary structure do not apply to polysaccharides.

Polysaccharides are formed from low molecular weight compounds called sugars or carbohydrates. 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 best known and most widely used is cellulose. In this polysaccharide, an oxygen bridge links the 1st and 4th carbon atoms in adjacent units, such a bond is called α-1,4-glycosidic.

The chemical composition similar to cellulose is starch, consisting of amylose and amylopectin, glycogen and dextran. The difference between the former and cellulose is the branching of macromolecules, and amylopectin and glycogen can be classified as hyperbranched natural polymers, i.e. dendrimers of irregular structure. The branch point is usually the sixth carbon of the α-D-glucopyranose ring, which is linked by a glycosidic bond to the side chain. The difference between dextran and cellulose is the nature of the glycosidic bonds - along with α-1,4-, dextran also contains α-1,3- and α-1,6-glycosidic bonds, the latter being dominant.

Chitin and chitosan have a chemical composition different from cellulose, but they are close to it in structure. The difference is that at the second carbon atom of α-D-glucopyranose units linked by α-1,4-glycosidic bonds, the OH group is replaced by –NHCH3COO groups in chitin and –NH2 group in chitosan.

Cellulose is found in the bark and wood of trees and plant stems: cotton contains more than 90% cellulose, coniferous trees - over 60%, deciduous trees - about 40%. The strength of cellulose fibers is due to the fact that they are formed by single crystals in which macromolecules are packed parallel to one another. Cellulose forms the structural basis of representatives not only of the plant world, but also of some bacteria.

In the animal world, polysaccharides are “used” only by insects and arthropods as supporting, structure-forming polymers. Most often, chitin is used for these purposes, which serves to build the so-called external skeleton in crabs, crayfish, and shrimp. From chitin, deacetylation produces chitosan, which, unlike insoluble chitin, is soluble in aqueous solutions of formic, acetic and hydrochloric acids. In this regard, and also due to the complex of valuable properties combined with biocompatibility, chitosan has great prospects for wide practical use in the near future.

Starch is one of the polysaccharides that act as a reserve food substance in plants. Tubers, fruits, and seeds contain up to 70% starch. The stored polysaccharide of animals is glycogen, which is found mainly in the liver and muscles.

The strength of plant trunks and stems, in addition to the skeleton of cellulose fibers, is determined by the connective plant tissue. A significant part of it in trees is lignin - up to 30%. Its structure has not been precisely established. It is known that this is a relatively low molecular weight (M ≈ 104) hyperbranched polymer, formed mainly from phenol residues substituted in the ortho position by –OCH3 groups, in the para position by –CH=CH–CH2OH groups. Currently, a huge amount of lignins has been accumulated as waste from the cellulose hydrolysis industry, but the problem of their disposal has not been solved. The supporting elements of plant tissue include pectin substances and, in particular, pectin, which is mainly found in cell walls. Its content in apple peels and the white part of citrus peels reaches up to 30%. Pectin belongs to heteropolysaccharides, i.e. copolymers. Its macromolecules are mainly constructed from residues of D-galacturonic acid and its methyl ester, linked by α-1,4-glycosidic bonds.

Among the pentoses, the most important are the polymers arabinose and xylose, which form polysaccharides called arabins and xylans. They, along with cellulose, determine the typical properties of wood.

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 of the amino acids 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 in any way 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 sections of the gene in which 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. Amino acids are sequentially added to the polypeptide chain in strict accordance with the sequence of columns on the mRNA.

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

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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).

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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 variable. Proteins interact with a wide variety of substances. 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.

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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.

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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.

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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.

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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 - 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.

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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.

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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.

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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:

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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.

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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.

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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

Most of modern building materials, medicines, fabrics, household items, packaging and consumables are polymers. This is a whole group of compounds that have characteristic distinctive features. There are a lot of them, but despite this, the number of polymers continues to grow. After all, synthetic chemists discover more and more new substances every year. At the same time, it was the natural polymer that was of particular importance at all times. What are these amazing molecules? What are their properties and what are their features? We will answer these questions during the article.

Polymers: general characteristics

From a chemical point of view, a polymer is considered to be a molecule with a huge molecular weight: from several thousand to millions of units. However, in addition to this characteristic, there are several more by which substances can be classified specifically as natural and synthetic polymers. This:

• constantly repeating monomer units that are connected through various interactions;
• the degree of polymerization (that is, the number of monomers) must be very high, otherwise the compound will be considered an oligomer;
• a certain spatial orientation of the macromolecule;
• a set of important physicochemical properties characteristic only of this group.

In general, a substance of a polymeric nature is quite easy to distinguish from others. One only has to look at its formula to understand this. A typical example is the well-known polyethylene, widely used in everyday life and industry. It is a product into which ethene or ethylene enters. The reaction in general form is written as follows:

nCH 2 =CH 2 → (-CH-CH-) n, where n is the degree of polymerization of the molecules, indicating how many monomer units are included in its composition.

Also, as an example, we can cite a natural polymer that is well known to everyone, this is starch. In addition, amylopectin, cellulose, chicken protein and many other substances belong to this group of compounds.

Reactions that can result in the formation of macromolecules are of two types:

• polymerization;
• polycondensation

The difference is that in the second case the reaction products are low molecular weight. The structure of a polymer can be different, it depends on the atoms that form it. Linear forms are common, but there are also three-dimensional mesh forms that are very complex.

If we talk about the forces and interactions that hold monomer units together, we can identify several main ones:

• Van Der Waals forces;
• chemical bonds (covalent, ionic);
• Electronostatic interaction.

All polymers cannot be combined into one category, since they have completely different natures, methods of formation and perform different functions. Their properties also differ. Therefore, there is a classification that allows you to divide all representatives of this group of substances into different categories. It may be based on several signs.

Classification of polymers

If we take the qualitative composition of molecules as a basis, then all the substances under consideration can be divided into three groups.

1. Organic are those that contain atoms of carbon, hydrogen, sulfur, oxygen, phosphorus, and nitrogen. That is, those elements that are biogenic. There are a lot of examples: polyethylene, polyvinyl chloride, polypropylene, viscose, nylon, natural polymer - protein, nucleic acids, and so on.
2. Organic elements are those that contain some foreign inorganic and non-organic element. Most often it is silicon, aluminum or titanium. Examples of such macromolecules: glass polymers, composite materials.
3. Inorganic - the chain is based on silicon atoms, not carbon. Radicals can also be part of side branches. They were discovered quite recently, in the middle of the 20th century. Used in medicine, construction, technology and other industries. Examples: silicone, cinnabar.

If we divide polymers by origin, we can distinguish three groups.

1. Natural polymers, the use of which has been widely carried out since ancient times. These are macromolecules for which man did not make any effort to create. They are products of reactions of nature itself. Examples: silk, wool, protein, nucleic acids, starch, cellulose, leather, cotton and others.
2. Artificial. These are macromolecules that are created by humans, but based on natural analogues. That is, the properties of an existing natural polymer are simply improved and changed. Examples: artificial
3. Synthetic polymers are those in which only humans are involved in their creation. There are no natural analogues for them. Scientists are developing methods for synthesizing new materials that would have improved technical characteristics. This is how synthetic polymer compounds of various kinds are born. Examples: polyethylene, polypropylene, viscose, etc.

There is one more feature that underlies the division of the substances under consideration into groups. These are reactivity and thermal stability. There are two categories for this parameter:

• thermoplastic;
• thermosetting.

The most ancient, important and especially valuable is still a natural polymer. Its properties are unique. Therefore, we will further consider this category of macromolecules.

What substance is a natural polymer?

To answer this question, let's first look around us. What surrounds us? Living organisms around us that eat, breathe, reproduce, bloom and produce fruits and seeds. What are they from a molecular point of view? These are connections such as:

• proteins;
• nucleic acids;
• polysaccharides.

So, each of the above compounds is a natural polymer. Thus, it turns out that life around us exists only due to the presence of these molecules. Since ancient times, people have used clay, building mixtures and mortars to strengthen and create homes, weave yarn from wool, and use cotton, silk, wool and animal skin to create clothing. Natural organic polymers accompanied man at all stages of his formation and development and largely helped him achieve the results that we have today.

Nature itself gave everything to make people’s lives as comfortable as possible. Over time, rubber was discovered and its remarkable properties were discovered. Man learned to use starch for food purposes and cellulose for technical purposes. Camphor, which has also been known since ancient times, is a natural polymer. Resins, proteins, nucleic acids are all examples of compounds considered.

Structure of natural polymers

Not all representatives of this class of substances are structured the same. Thus, natural and synthetic polymers can differ significantly. Their molecules are oriented in such a way that they exist as advantageously and conveniently as possible from an energetic point of view. At the same time, many natural species are capable of swelling and their structure changes in the process. There are several most common variants of the chain structure:

• linear;
• branched;
• star-shaped;
• flat;
• mesh;
• tape;
• comb-shaped.

Artificial and synthetic representatives of macromolecules have a very large mass and a huge number of atoms. They are created with specially specified properties. Therefore, their structure was initially planned by man. Natural polymers are most often either linear or network in structure.

Examples of natural macromolecules

Natural and artificial polymers are very close to each other. After all, the former become the basis for creating the latter. There are many examples of such transformations. Let's list some of them.

1. Conventional milky-white plastic is a product obtained by treating cellulose with nitric acid with the addition of natural camphor. The polymerization reaction causes the resulting polymer to solidify into the desired product. And the plasticizer, camphor, makes it capable of softening when heated and changing its shape.
2. Acetate silk, copper-ammonia fiber, viscose - all these are examples of those threads and fibers that are obtained from cellulose. Fabrics made from linen are not so durable, not shiny, and easily wrinkled. But artificial analogues do not have these disadvantages, which makes their use very attractive.
3. Artificial stones, building materials, mixtures, leather substitutes are also examples of polymers obtained from natural raw materials.

The substance, which is a natural polymer, can be used in its true form. There are also many such examples:

• rosin;
• amber;
• starch;
• amylopectin;
• cellulose;
• wool;
• cotton;
• silk;
• cement;
• clay;
• lime;
• proteins;
• nucleic acids and so on.

It is obvious that the class of compounds we are considering is very numerous, practically important and significant for people. Now let's take a closer look at several representatives of natural polymers that are in great demand at the present time.

Silk and wool

The formula of natural silk polymer is complex, because its chemical composition is expressed by the following components:

• fibroin;
• sericin;
• waxes;
• fats.

The main protein itself, fibroin, contains several types of amino acids. If you imagine its polypeptide chain, it will look something like this: (-NH-CH 2 -CO-NH-CH(CH 3)-CO-NH-CH 2 -CO-) n. And this is just part of it. If we imagine that an equally complex sericin protein molecule is attached to this structure with the help of Van Der Waals forces, and together they are mixed into a single conformation with wax and fats, then it is clear why it is difficult to depict the formula of natural silk.

Today, most of this product is supplied by China, because in its vastness there is a natural habitat for the main producer - the silkworm. Previously, since ancient times, natural silk was highly valued. Only noble, rich people could afford clothes made from it. Today, many characteristics of this fabric leave much to be desired. For example, it becomes highly magnetized and wrinkles; in addition, it loses its luster and becomes dull when exposed to the sun. Therefore, artificial derivatives based on it are more common.

Wool is also a natural polymer, as it is a waste product of the skin and sebaceous glands of animals. Based on this protein product, knitwear is made, which, like silk, is a valuable material.

Starch

The natural polymer starch is a waste product of plants. They produce it through the process of photosynthesis and accumulate it in different parts of the body. Its chemical composition:

• amylopectin;
• amylose;
• alpha glucose.

The spatial structure of starch is very branched and disordered. Thanks to the amylopectin it contains, it is able to swell in water, turning into a so-called paste. This one is used in engineering and industry. Medicine, the food industry, and the production of wallpaper adhesives are also areas of use of this substance.

Among the plants containing the maximum amount of starch are:

• corn;
• potato;
• wheat;
• cassava;
• oats;
• buckwheat;
• bananas;
• sorghum.

Based on this biopolymer, bread is baked, pasta is made, jelly, porridge and other food products are cooked.

Cellulose

From a chemical point of view, this substance is a polymer, the composition of which is expressed by the formula (C 6 H 5 O 5) n. The monomeric unit of the chain is beta-glucose. The main places where cellulose is contained are the cell walls of plants. That is why wood is a valuable source of this compound.

Cellulose is a natural polymer that has a linear spatial structure. It is used to produce the following types of products:

• pulp and paper products;
• faux fur;
• different types of artificial fibers;
• cotton;
• plastics;
• smokeless powder;
• films and so on.

It is obvious that its industrial significance is great. In order for this compound to be used in production, it must first be extracted from plants. This is done by long-term cooking of wood in special devices. Further processing, as well as the reagents used for digestion, vary. There are several ways:

• sulfite;
• nitrate;
• soda;
• sulfate.

After this treatment, the product still contains impurities. It is based on lignin and hemicellulose. To get rid of them, the mass is treated with chlorine or alkali.

There are no biological catalysts in the human body that would be able to break down this complex biopolymer. However, some animals (herbivores) have adapted to this. Certain bacteria settle in their stomach and do this for them. In return, microorganisms receive energy for life and a habitat. This form of symbiosis is extremely beneficial for both parties.

Rubber

It is a natural polymer of valuable economic importance. It was first described by Robert Cook, who discovered it on one of his travels. It happened like this. Having landed on an island where natives unknown to him lived, he was hospitably received by them. His attention was attracted by local children who were playing with an unusual object. This spherical body pushed off from the floor and jumped high up, then returned.

Having asked the local population what this toy was made of, Cook learned that this is how the sap of one of the trees, the Hevea, solidifies. Much later it was found out that this is the biopolymer rubber.

The chemical nature of this compound is known - it is isoprene that has undergone natural polymerization. Rubber formula (C 5 H 8) n. Its properties, due to which it is so highly valued, are as follows:

• elasticity;
• wear resistance;
• electrical insulation;
• waterproof.

However, there are also disadvantages. In the cold it becomes brittle and brittle, and in the heat it becomes sticky and viscous. That is why there was a need to synthesize analogues of an artificial or synthetic base. Today, rubbers are widely used for technical and industrial purposes. The most important products based on them:

• rubber;
• ebony.

Amber

It is a natural polymer, since its structure is a resin, its fossil form. The spatial structure is a framework amorphous polymer. It is very flammable and can be ignited with a match flame. Has luminescent properties. This is a very important and valuable quality that is used in jewelry. Amber-based jewelry is very beautiful and in demand.

In addition, this biopolymer is also used for medical purposes. Sandpaper and varnish coatings for various surfaces are also made from it.

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