Amines. These organic compounds are derivatives of ammonia. They can be considered as products of substitution of one, two or three hydrogen atoms in the ammonia molecule by hydrocarbon radicals:
H ─ N: CH 3 ─ N: CH 3 ─ N: CH 3 ─ N:
ammonia methylamine dimethylamine trimethylamine
Amines are organic bases. Due to the lone pair of electrons at the nitrogen atom, their molecules, like the ammonia molecule, can attach protons:
CH 3 ─ N: + Н─О─Н → CH 3 ─ N─Н OH -
methylammonium hydroxide
Amino acids and proteins
big biological significance have amino acids- compounds with mixed functions, which, like amines, contain amino groups ─ NH 2 and at the same time, like acids, carboxyl groups ─ COOH.
The structure of amino acids is expressed by the general formula (where R is a hydrocarbon radical, which may contain various functional groups):
H 2 N─CH ─ C─OH
H 2 N─CH 2 ─ C─OH H 2 N─CH ─ C─OH
glycine alanine
Amino acids are amphoteric compounds: they form salts with bases (due to the carboxyl group) and with acids (due to the amino group).
The hydrogen ion, split off during dissociation from the amino acid carboxyl, can pass to its amino group with the formation of an ammonium group. thus, amino acids exist and react also in the form of bipolar ions (internal salts):
H 2 N─CH ─ COOH ↔ H 3 N + ─CH ─ COO -
amino acid bipolar ion
(internal salt)
This explains that solutions of amino acids containing one carboxyl and one amino group have a neutral reaction.
Molecules of protein substances, or proteins, are built from amino acid molecules, which, when completely hydrolyzed under the influence of mineral acids, alkalis or enzymes, decompose, forming mixtures of amino acids.
Squirrels- natural high-molecular nitrogen-containing organic compounds. They play a primary role in all life processes, they are carriers of life.
Proteins are made up of carbon, hydrogen, oxygen, nitrogen, and often sulfur, phosphorus, and iron. The molecular weights of proteins are very large - from 1500 to several million.
The structure of a protein molecule can be represented as follows:
R R′ R R" R"′
│ │ │ │ │
H 2 N─CH ─ C─... НN─CH ─ C─.... НN─CH ─ C─... НN─CH ─ C─.... НN─CH ─ C─OH
║ ║ ║ ║ ║
In protein molecules, groups of atoms ─СО─NH─ are repeated many times; they are called amide groups, or in protein chemistry - peptide groups.
Tasks, control questions
1. How many m 3 of carbon monoxide (IV) is formed during combustion: a) 5 m 3 of ethane; b) 5 kg of ethane (n.o.s.)?
2. Write the structural formulas of normal alkenes containing: a) four; b) five; c) six carbon atoms.
3. Write the structural formula of n-propanol.
4. What compounds are carbonyl? Give examples, write structural formulas and indicate the carbonyl group in them.
5. What are carbohydrates? Give examples.
The most important organic and inorganic polymers,
their structure and classification
High molecular weight compounds, or polymers, are called complex substances with large molecular weights (on the order of hundreds, thousands, millions), the molecules of which are built from many repeating elementary units, formed as a result of the interaction and combination with each other of the same or different simple molecules - monomers.
Oligomer- a molecule in the form of a chain of a small number of identical constituent units. This distinguishes oligomers from polymers, in which the number of units is theoretically unlimited. The upper limit of the mass of an oligomer depends on its chemical properties. The properties of oligomers are highly dependent on changes in the number of repeating units in the molecule and the nature of the end groups; from the moment when the chemical properties cease to change with increasing chain length, the substance is called a polymer.
Monomer- a substance consisting of molecules, each of which can form one or more constituent units.
Composite link- an atom or a group of atoms that make up the chain of an oligomer or polymer molecule.
Degree of polymerization- the number of monomer units in the macromolecule.
Molecular mass is an important characteristic of macromolecular compounds - polymers, which determines their physical (and technological) properties. The number of monomer units that make up different molecules of the same polymeric substance is different, as a result of which the molecular weight of polymer macromolecules is also not the same. Therefore, when characterizing a polymer, one speaks of the average value of the molecular weight. Depending on the method of averaging - the principle underlying the method for determining the molecular weight, there are three main types of molecular weights.
Number average molecular weight- averaging over the number of macromolecules in the polymer:
v i-number fraction of macromolecules with molecular weight M i , N- number of fractions
Weight average molecular weight- averaging over the mass of molecules in the polymer:
Where w i- mass fraction of molecules with molecular weight Mi.
Molecular weight distribution (MWD) of the polymer (or its polydispersity) - is its most important characteristic and is determined by the ratio of the quantities n i macromolecules with different molecular weights M i in this polymer. MWD has a significant effect on the physical characteristics of polymers, and, above all, on the mechanical properties.
MWD characterize the numerical and mass fraction of macromolecules whose molecular weights (M) lie in the range from M before M+dM. Determine the numerical and mass differential functions of the MMP:
dN M- the number of macromolecules in the interval dM;
dm M- mass of macromolecules in the interval dM;
N0- the total number of macromolecules in a sample with a mass m0.
For a quantitative comparison of the MWD of various polymers, the ratios of the average values of their molecular weights are used.
Classification of polymers
By origin, polymers are divided into:
natural (biopolymers), e.g. proteins, nucleic acids, natural resins,
And synthetic eg polyethylene, polypropylene, phenol-formaldehyde resins.
Atoms or atomic groups can be arranged in a macromolecule in the form:
an open chain or a sequence of cycles stretched into a line ( linear polymers e.g. natural rubber);
branched chains ( branched polymers such as amylopectin)
3D grid ( crosslinked polymers, network, or spatial, are called polymers built from long chains connected to each other in a three-dimensional grid by transverse chemical bonds; e.g. cured epoxy resins). Polymers whose molecules consist of identical monomeric units are called homopolymers(e.g. polyvinyl chloride, polycaproamide, cellulose).
Macromolecules of the same chemical composition can be built from units of different spatial configurations. If macromolecules consist of the same stereoisomers or of different stereoisomers alternating in a chain at a certain periodicity, polymers are called stereoregular.
Polymers whose macromolecules contain several types of monomer units are called copolymers.
Copolymers in which links of each type form sufficiently long continuous sequences that replace each other within the macromolecule are called block copolymers.
One or more chains of another structure can be attached to the internal (non-terminal) links of a macromolecule of one chemical structure. Such copolymers are called vaccinated.
Polymers in which each or some of the stereoisomers of the link form sufficiently long continuous sequences that replace each other within one macromolecule are called stereoblock copolymers.
Depending on the composition of the main (main) chain, polymers are divided into: heterochain, the main chain of which contains atoms of various elements, most often carbon, nitrogen, silicon, phosphorus,
And homochain, the main chains of which are built from identical atoms.
Of the homochain polymers, the most common are carbon chain polymers, the main chains of which consist only of carbon atoms, for example, polyethylene, polymethyl methacrylate, polytetrafluoroethylene.
Examples of heterochain polymers are polyesters (polyethylene terephthalate, polycarbonates), polyamides, urea-formaldehyde resins, proteins, some organosilicon polymers.
Polymers whose macromolecules, along with hydrocarbon groups, contain atoms of inorganic elements are called organoelement. A separate group of polymers is formed by inorganic polymers, such as plastic sulfur, polyphosphonitrile chloride.
The most important natural and artificial polymers. Biopolymers.
Examples of natural macromolecular compounds (biopolymers) are starch and cellulose, built from elementary units, which are monosaccharide (glucose) residues, as well as proteins, whose elementary units are amino acid residues; this also includes natural rubbers.
Currently, a huge number of artificial polymers have been created. On the basis of them receive plastics (plastics) - complex compositions into which various fillers and additives are introduced that give the polymers the necessary set of technical properties - as well as synthetic fibers and resins.
Polyethylene- a polymer formed during the polymerization of ethylene, for example, by compressing it to 150-250 MPa at 150-200 0 C (high pressure polyethylene)
CH 2 \u003d CH 2 + CH 2 \u003d CH 2 + CH 2 \u003d CH 2 → ... ─CH 2 ─CH 2 ─CH 2 ─CH 2 ─CH 2 ─CH 2 ─CH 2 ─ ...
polyethylene
or n CH 2 \u003d CH 2 → (─ CH 2 ─ CH 2 ─) n
Polyethylene is a saturated hydrocarbon with a molecular weight of 10,000 to 400,000. It is a colorless translucent in thin and white in thick layers, a waxy but solid material with a melting point of 110-125 0 C. It has high chemical resistance and water resistance, low gas permeability .
Polypropylene- propylene polymer
n
CH 3 CH 3 CH 3
propylene polypropylene
Depending on the polymerization conditions, polypropylene is obtained, which differs in the structure of macromolecules, a. hence, properties. By appearance it is a rubbery mass, more or less hard and resilient. Differs from polyethylene in higher melting point.
Polystyrene
n CH 2 \u003d CH → ─CH 2 ─CH─CH 2 ─CH─
C 6 H 5 C 6 H 5 C 6 H 5
styrene polystyrene
PVC
n CH 2 \u003d CH → ─CH 2 ─CH─CH 2 ─CH─
vinyl chloride polyvinyl chloride
It is an elastic mass, very resistant to acids and alkalis.
Polytetrafluoroethylene
n CF 2 \u003d C F 2 → (─ CF─CF─) n
tetrafluoroethylene polytetrafluoroethylene
Polytetrafluoroethylene comes in the form of a plastic called Teflon, or PTFE. Very resistant to alkalis and concentrated acids, surpasses gold and platinum in chemical resistance. Non-flammable, has high dielectric properties.
Rubbers- elastic materials, from which rubber is obtained by special processing.
Natural (natural) rubber is a high molecular weight unsaturated hydrocarbon, whose molecules contain a large number of double bonds, its composition can be expressed by the formula (C 6 H 8) n(where the value n ranges from 1000 to 3000); it is a polymer of isoprene:
n CH 2 \u003d C ─ CH \u003d CH 2 → ─ CH 2 ─ C \u003d CH ─ CH 2 ─
CH 3 CH 3 n
natural rubber (polyisoprene)
Many different types of synthetic rubbers are currently being produced. The first synthesized rubber (the method was proposed by S.V. Lebedev in 1928) is polybutadiene rubber:
n CH 2 = CH─CH=CH 2 → (─CH 2 ─CH=CH─CH 2 ─) n
Amino acids are the main structural components of protein molecules and appear in free form in food products in the process of protein breakdown.
amino acid amides contained in plant Products as a natural constituent. For example, asparagine amide (0.2-0.3%) is found in cabbage and asparagus.
Ammonia compounds found in food products in small quantities in the form of ammonia and its derivatives. Ammonia is the end product of protein breakdown. A significant amount of ammonia and amines indicates the putrefactive decomposition of food proteins. Therefore, when studying the freshness of meat and fish, the content of ammonia in them is determined. Ammonia derivatives include monoamines CH 3 NH 2, dimethylamines (CH 3) 2 NH and trimethylamines (CH 3) 3 N, which have a specific odor. Methylamine has an odor similar to ammonia. Dimethylamine - a gaseous substance with the smell of herring brine, is formed mainly during the decay of fish proteins and other products. Trimethylamine is a gaseous substance found in significant quantities in herring brine. In concentrated form, it smells like ammonia, but in low concentrations it smells like rotten fish.
Nitrates- salts of nitric acid. It is contained in food products in small quantities, with the exception of pumpkin and zucchini.
Nitrites added in small quantities when salting meat and in minced meat to give the meat a pink color. Nitrites are highly toxic, so their use in the food industry is limited (nitrite solution is added to minced meat at the rate of not more than 0.005% of the meat mass).
Squirrels are the most important nitrogen-containing compounds for human nutrition. They are the most important organic compounds found in living organisms. Back in the last century, studying the composition of various animals and plants, scientists isolated substances that, in some properties, resembled egg white: for example, when heated, they coagulated. This gave reason to call them proteins. The importance of proteins as the basis of all living things was noted by F. Engels. He wrote that where there is life, proteins are found, and where proteins are present, signs of life are noted.
Thus, the term "proteins" is called big class organic high-molecular nitrogen-containing compounds present in every cell and determining its vital activity.
Chemical composition proteins. Chemical analysis showed the presence in all proteins (in%): carbon - 50-55, hydrogen - 6-7, oxygen - 21-23, nitrogen - 15-17, sulfur - 0.3-2.5. Phosphorus, iodine, iron, copper and some macro- and microelements were found in individual proteins in various amounts.
To determine the chemical nature of protein monomers, hydrolysis is carried out - prolonged boiling of a protein with strong mineral acids or bases. Most often, 6N HN0 3 and boiling at 110°C for 24 hours are used. At the next stage, the substances that make up the hydrolyzate are separated. For this purpose, the method of chromatography is used. Finally, the nature of the isolated monomers is elucidated using certain chemical reactions. As a result, it was found that the initial components of proteins are amino acids.
Molecular weight (m.m.) of proteins from 6000 to 1,000,000 and above, so, m.m. milk albumin protein - 17400, milk globulin - 35200, egg albumin - 45000. In the body of animals and plants, protein occurs in three states: liquid (milk, blood), syrupy (egg white) and solid (skin, hair, wool).
Thanks to the large mm. proteins are in a colloidal state and are dispersed (distributed, dispersed, suspended) in a solvent. Most proteins are hydrophilic compounds that are able to interact with water, which binds to proteins. This interaction is called hydration.
Many proteins under the influence of some physical and chemical factors (temperature, organic solvents, acids, salts) coagulate and precipitate. This process is called denaturation. Denatured protein loses its ability to dissolve in water, salt solutions or alcohol. All food products processed with high temperatures contain denatured protein. Most proteins have a denaturation temperature of 50-60°C. The property of proteins to denature is important, in particular, when baking bread and obtaining confectionery. One of the important properties of proteins is the ability to form gels when swollen in water. The swelling of proteins has great importance in the production of bread, pasta and other products. During “aging”, the gel gives off water, while decreasing in volume and wrinkling. This phenomenon, the opposite of swelling, is called syneresis.
If protein products are stored incorrectly, deeper decomposition of proteins can occur with the release of amino acid breakdown products, including ammonia and carbon dioxide. Proteins containing sulfur release hydrogen sulfide.
A person needs 80-100 g of proteins per day, including 50 g of animal proteins. When 1 g of protein is oxidized in the body, 16.7 kJ, or 4.0 kcal, is released.
Amino acids - these are organic acids in which the hydrogen atom of the oc-carbon atom is replaced by an amino group NH 2. Therefore, it is an oc-amino acid with the general formula
It should be noted that in the composition of all amino acids there are common groups: -CH 2, -NH 2, -COOH, and the side chains of amino acids, or radicals (R), differ. The chemical nature of radicals is diverse: from a hydrogen atom to cyclic compounds. It is the radicals that determine the structural and functional features of amino acids.
Amino acids in an aqueous solution are in an ionized state due to the dissociation of amine and carboxyl groups, as well as groups that make up the radicals. In other words, they are amphothermic compounds and can exist either as acids (proton donors) or as bases (proton acceptors).
All amino acids, depending on the structure, are divided into several groups.
Of the 20 amino acids that are involved in building proteins, not all have the same biological value. Some amino acids are synthesized by the human body, and the need for them is satisfied without being supplied from outside. Such amino acids are called non-essential (histidine, arginine, cystine, tyrosine, alanine, series, glutamic and aspartic acids, proline, hydroxyproline, glycine). The other part of the amino acids is not synthesized by the body and they must be supplied with food. They are called essential (tryptophan). Proteins containing all the essential amino acids are called complete, and if at least one of the essential acids is missing, the protein is defective.
Classification of proteins. The classification of proteins is based on their physicochemical and chemical features. Proteins are divided into simple (proteins) and complex (proteins). Simple proteins are proteins that, when hydrolyzed, yield only amino acids. To complex - proteins consisting of simple proteins and compounds of a non-protein group called prosthetic.
Proteins include albumins (milk, eggs, blood), globulins (blood fibrinogen, meat myosin, egg globulin, potato tuberin, etc.), glutelins (wheat and rye), prodamins (wheat gliadin), scleroproteins (bone collagen, connective elastin tissue, hair keratin).
Proteins include phosphoproteins (milk casein, vitellin chicken egg, ichthulin fish caviar), which consist of protein and phosphoric acid; chromoproteins (blood hemoglobin, meat muscle myoglobin), which are compounds of globin protein and a dye; glucolroteids (proteins of cartilage, mucous membranes), consisting of simple proteins and glucose; lipoproteins (proteins containing phosphatide) are part of the protoplasm and chlorophyll grains; nucleoproteins contain nucleic acids and play an important biological role for the body.
Many of the non-protein nitrogen-containing substances are intermediate or end products of the protein metabolism of plant and animal organisms. . Non-protein nitrogen-containing substances are involved in the formation of a specific taste and aroma of products. Some of them stimulate the activity of the digestive glands.
Amino acids are the main structural components of protein molecules and appear in free form in foods mainly in the process of protein breakdown. Free amino acids are found in plant and animal tissues in small quantities. When food is stored, their number increases.
Acid amides are derivatives of fatty acids with the general formula RCH 2 CONH 2. They are common in plant and animal products as a natural constituent. These include asparagine, glutamine, urea, etc.
Ammonia compounds are found in foodstuffs in small quantities in the form of ammonia and its derivatives, in particular amines. A significant content of ammonia and amines indicates the putrefactive decomposition of food proteins. Ammonia derivatives include methylamines CH 3 NH 2, dimethylamines (CH 3) 2 NH, and trimethylamines (CH 3) 3 N which have a specific odor. When the proteins of meat and fish rot, amines that are poisonous to humans are formed - cadaverine, putrescine, histamine .
Nitrates, i.e. salts of nitric acid, as a natural food compound, are found in small quantities, but in some products the amount of nitrates is significant. At present, the maximum permissible concentrations (MPC) of nitrates in various types vegetables and fruits.
In the human body, under the influence of intestinal microflora, nitrates are reduced to nitrites, which are absorbed into the blood and block the centers of respiration. The maximum allowable dose of nitrates for a person should not exceed 5 mg per 1 kg of body weight.
nitrites, in particular, NaNO 2 is added to meat as a preservative in the production of sausages, smoked meats, corned beef, to preserve the pink-red color of finished products. Nitrites are more toxic than nitrates; in the human stomach, nitrosamines are formed from them - the strongest of the currently known chemical carcinogens. The maximum allowable daily dose for them is 0.4 mg per 1 kg of human body weight. The sanitary legislation establishes the maximum allowable norm for the content of nitrites in meat products.
alkaloids - a group of physiologically active nitrogen-containing compounds that have basic properties and have a heterocyclic structure. Many of them in large doses are potent poisons.
Alkaloids include nicotine C 10 H 14 N 2, caffeine C 8 H 10 N 4 O 2 and theobromine C 7 H 8 N 4 O 2. The lethal dose of nicotine for humans is 0.01-0.04 g. A sharp burning taste is given to products by alkaloids - piperine C 17 H 19 O 3 N and piperovatin C 16 H 21 O 2 N (in hot pepper), etc.
Purine nitrogenous bases - adenine C 5 H 5 N 5, guanine C 5 H 5 N 5 O, xanthine, C 5 H 5 N 4 O 2, hypoxanthine C 5 H 4 N 4 O - occur during the hydrolysis of nucleic acids, are found in the muscles of animals and fish, tea, yeast, brain tissue. These are biologically active substances.
Organic compounds containing nitrogen atoms are classified as nitrogen-containing organic substances. The nature of these compounds is very diverse, they form a large number of classes of organic substances.
This chapter discusses the most important nitrogen-containing organic compounds: nitro compounds, nitric acid esters, amines, amino acids, proteins, nitrogenous bases and nucleic acids.
Nitro compounds- derivatives of hydrocarbons, in the molecules of which the hydrogen atoms are replaced by the nitro group -N0 2 .
Nitro compounds have a complex classification, since they differ in the number of nitro groups in the molecule, contain various radicals, etc. Let's consider some groups of nitro compounds.
- 1. According to the nature of the hydrocarbon radical, they are divided into marginal(nitromethane CH 3 N0 2), unlimited(3-nitropropene-1 CH 2 \u003d CH-CH 2 N0 2), aromatic(nitrobenzene C 6 H 5 N0 2), etc.
- 2. According to the number of nitro groups, they distinguish mononitro compounds(see examples above); dinitro compounds(dinitrobenzenes C 6 H 4 (N0 2) 2 - various isomers); trinitro compounds(1,3,5- trinitrobenzene C 6 H 3 (N0 2) 3), etc.
Nitro compounds are obtained as a result of nitration reactions, which are carried out by heating in the presence of catalysts (each case has its own conditions):
(for the nitration of hydrocarbons, see 12.3).
There are nitro compounds whose molecules contain other functional groups, such as trinitrophenol (see 14.8) and others.
The physical and chemical properties of nitro compounds are diverse.
In genetic terms, the most important is their ability to be reduced by atomic hydrogen. (Zinin reaction) -, in this case, amines are formed:
Nitric acid esters are functionally close to nitro compounds, for example, trinitroglycerin (see 14.7), trinitrocellulose (see 14.26) and other similar compounds.
One of the most important properties of substances containing nitro groups is their ability to explode (brisance), so they are used in the production of blasting. Some compounds (trinitroglycerin) are used in medicine. Nitro compounds are used to obtain amines, as well as in various organic syntheses.
These compounds require careful handling due to their explosive potential as well as their toxicity. Toxicity and brisance determine the negative ecological role of nitro compounds.
- ? Tasks for independent work
- 1. Explain why nitro compounds are classified as nitrogen-containing organic substances; Give two examples of these substances.
- 2. Name three groups of nitro compounds based on the nature of the hydrocarbon radicals they contain.
- 3. Give two reasonable examples illustrating the areas of use of nitro compounds.
- 4. Give two justified examples illustrating the ecological role of nitro compounds.
Back forward
Attention! The slide preview is for informational purposes only and may not represent the full extent of the presentation. If you are interested in this work, please download the full version.
Lesson Objectives:
- Update students' knowledge of natural polymers using proteins as an example. Describe the composition, structure, properties and functions of proteins.
- To promote the development of attention, memory, logical thinking, the ability to compare and analyze.
- Formation of students' interest in this topic, communicative qualities.
Lesson type: a lesson in the formation of new knowledge.
Educational Resources:
- Library of electronic visual aids "Chemistry grades 8-11", developer "Cyril and Methodius", 2005
- Electronic edition “Chemistry 8-11. Virtual laboratory”, developed by Mar GTU, 2004
- Electronic edition of the course "Biotechnology", developer "New Disk", 2003
Material and technical equipment, didactic support: Computer, projector, screen. Presentation "Protein". Proc. Rudzitis G.E. Chemistry 10th grade 2011, Proc. Yu.I. Polyansky. General biology.10–11th grade. 2011
Laboratory equipment and reagents: Protein solution, sodium hydroxide, lead acetate, copper sulfate, concentrated nitric acid, spirit lamp, holder, test tubes.
During the classes
I. Organizational moment(3–5’)
II. Message about the topic and purpose of the lesson (3–5’). (Slide 1-2)
III. Explanation of the material on the topic “ Nitrogen-containing organic compounds. Squirrels".
1. Proteins (Slide 3). We begin the study of protein with the statement of the biochemist J. Mulder “In all plants and animals there is a certain substance, which without a doubt is the most important of all known substances of living nature and without which life would be impossible on our planet.”
2. Determination of protein (Slide 4-6) Students discuss and write in a notebook.
Slide 4. Determination of proteins. Proteins are nitrogen-containing macromolecular organic substances with a complex composition and molecular structure.
Slide 5. Proteins, along with carbohydrates and fats, are the main component of our food.
Slide 6. Protein is the highest form of development of organic substances. All life processes are associated with proteins. Proteins are part of the cells and tissues of all living organisms. The content of proteins in different cells can vary from 50 to 80%.
3. History of protein (Slide 7-11). Acquaintance with the first protein researchers( Jacopo Bartolomeo Beccari, Francois Quesnet, Antoine Francois de Fourcroix).
Slide 7. The name of the squirrel comes from the egg white. In ancient Rome, egg white was used as a remedy. The true history of proteins begins when the first information about their properties appears.
Slide 6. For the first time, protein was isolated (in the form of gluten) in 1728 by the Italian Ya.B. Beccari made from wheat flour. This event is considered to be the birth of protein chemistry. It was soon discovered that similar compounds are found in all organs of not only plants, but also animals. This fact was very surprising to scientists who are accustomed to dividing substances into compounds of the “animal and plant world”. A common feature of the new substances was that when heated, they released substances of the main nature - ammonia and amines.
Slide 9. 1747 - French physiologist F.Kene first applied the term "protein" to the fluids of a living organism.
Slide 10. In 1751, the term protein was included in the "Encyclopedia" by D. Diderot and J. Alembert.
4. Protein composition (Slide 12) students write in a notebook.
Slide 12. Protein composition . The elemental composition of the protein varies slightly (in % of dry weight): C - 51-53%, O - 21.5–23.5%, N - 16.8–18.4%, H - 6.5–7.3%, S - 0.3–2.5%. Some proteins contain P, Se, etc.
5. The structure of the protein (Slide 13-15).
Slide 13. Proteins are natural polymers, the molecules of which are built from amino acid residues connected by a peptide bond. There are 51 residues in insulin and 140 in myoglobin.
The relative molecular weight of proteins is very large, ranging from 10 thousand to many millions. For example: insulin - 6500, egg protein - 360,000, and one of the muscle proteins reaches 150,000.
Slide 14. Over 150 amino acids have been found in nature, but only about 20 amino acids are found in proteins.
Slide 15. Students repeat the definition, name and structure of amino acids. Amino acids called nitrogen-containing organic compounds, the molecules of which contain amino groups - NH 3 and carboxyl groups - COOH.
Amino acids can be considered as derivatives of carboxylic acids in which the hydrogen atom in the radical is replaced by an amino group.
6. Peptide theory of protein structure (Slide 16-19). Question to students – What is a peptide bond?
A peptide bond is a bond forming between the residue - NH - of the amino group of one amino acid molecule and the residue - CO - of the carboxyl group of another amino acid molecule.
Slide 16. By the beginning of the 19th century, new works on the chemical study of proteins appeared. Fischer Emil German in 1902 proposed the peptide theory of protein structure, experimentally proved that amino acids bind to form compounds, which he called polypeptides. Nobel Prize winner in 1902.
Slide 17. Proteins include several hundred and sometimes thousands of combinations of basic amino acids. The order of their alternation is the most diverse. Each amino acid can occur several times in a protein. For a protein consisting of 20 amino acid residues, about 2x10 18 variants are theoretically possible (one of the variants).
Slide 18. A polymer consisting of amino acids (second option).
19 slide. A chain consisting of a large number of amino acid residues connected to each other is called a polypeptide. It consists of tens and hundreds of amino acid residues. All proteins have the same polypeptide backbone. There are 3.6 amino acid residues per turn of the helix.
7. Classification of proteins (Slide 20). Student's report on the topic “Several classifications of proteins”.(Annex 2).
8. Structure of a protein molecule (Slide 21-29). When studying the composition of proteins, it was found that all proteins are built according to a single principle and have four levels of organization. The students are listening,discuss and write down the definition of the structures of the protein molecule.
Slide 21. Structure of a protein molecule . In the first half of the 19th century, it became clear that proteins are an integral part of all living substances on Earth without exception. The discovery of amino acids, the study of the properties and methods for obtaining peptides were a step towards establishing the structure of protein molecules. When studying the composition of proteins, it was found that they are all built according to a single principle and have four levels of organization: primary, secondary, tertiary, and some of them also have quaternary structures.
Slide 22. The primary structure of a protein. It is a linear chain of amino acid residues arranged in a certain sequence and interconnected by peptide bonds. The number of amino acid units in a molecule can vary from several tens to hundreds of thousands. This is reflected in the molecular weight of proteins, which varies widely: from 6500 (insulin) to 32 million (influenza virus protein). The primary structure of a protein molecule plays an extremely important role. Changing only one amino acid to another can lead either to the death of the organism, or to the appearance of an entirely new species.
slide 23. Repetition of the mechanism of peptide bond formation.
Students receive the task: Write an equation for the reaction of obtaining a dipeptide from any two amino acids from the proposed list (a table of amino acids is attached). Checking the completed task.
Slide 24. Danilevsky A.Ya. - Russian biochemist, academician. One of the founders of Russian biochemistry. Worked in the field of enzymes and proteins. In 1888 Danilevsky A.Ya. proposed a theory of the structure of the protein molecule (the existence of peptide bonds in proteins). Experimentally proved that proteins undergo hydrolysis under the action of pancreatic juice. Studied muscle proteins (myosin), discovered antipepsin and antitrypsin.
Slide 25. The secondary structure of a protein is a polypeptide chain twisted into a spiral. It is held in space due to the formation of numerous hydrogen bonds between the groups - CO - and - NH - located on adjacent turns of the helix. There are two classes of such structures - helical and folded. All of them are stabilized by hydrogen bonds. The polypeptide chain can be twisted into a helix, on each turn of which there are 3.6 amino acid units with radicals facing outward. Individual turns are held together by hydrogen bonds between groups of different sections of the chain. Such a protein structure is called a helix and is observed, for example, in keratin (wool, hair, horns, nails). If the side groups of amino acid residues are not very large (glycine, alanine, serine), two polypeptide chains can be arranged in parallel and held together by hydrogen bonds. In this case, the strip is not flat, but folded. This is a protein structure, characteristic, for example, of silk fibroin.
Slide 26. In 1953, L. Pauling developed a model for the secondary structure of a protein. In 1954 he was awarded Nobel Prize in chemistry. In 1962 - the Nobel Peace Prize.
Slide 27. Tertiary structure is the way a spiral or structure is arranged in space. This is a real three-dimensional configuration of a polypeptide chain helix twisted in space (i.e. a helix twisted into a helix).
Slide 28. The tertiary structure is supported by the bonds that arise between the functional groups of the radicals. – disulfide bridges (–S–S–) between sulfur atoms (between two cysteine residues of different parts of the chain), – ester bridges between the carboxyl group (–COOH) and the hydroxyl group (–OH), – salt bridges between the carboxyl group (–COOH ) and an amino group (–NH 2) . According to the shape of the protein molecule, which is determined by the tertiary structure, globular proteins (myoglobin) and fibrillar (hair keratin) proteins are isolated, which perform a structural function in the body.
Slide 29. Quaternary structure is a form of interaction between several polypeptide chains. Between themselves, the polypeptide chains are connected by hydrogen, ionic, hydrophobic, and other bonds. Student's report on the topic “The quaternary structure of a protein molecule”. (Annex 3).
9. Chemical properties proteins (Slide 30). Of the chemical properties, we consider the following properties: denaturation, hydrolysis and color reactions to protein.
slide 30. The properties of proteins are diverse: some proteins are solids, insoluble in water and saline solutions; most proteins are liquid or gelatinous, water-soluble substances (for example, albumin is a protein of a chicken egg). The protoplasm of cells consists of a colloidal protein.
Slide 31. Protein denaturation is the destruction of the secondary, tertiary and quaternary structures of a protein molecule under the influence of external factors. Reversible denaturation is possible in solutions of ammonium, potassium and sodium salts. Under the influence of heavy metal salts, irreversible denaturation occurs. Therefore, vapors of heavy metals and their salts are extremely harmful to the body. For disinfection, preservation, etc., formalin, phenol, ethyl alcohol are used, the action of which also leads to irreversible denaturation. Protein during denaturation loses a number of the most important functions of the living structure: enzymatic, catalytic, protective, etc.
10. Denaturation of proteins (Slide 31-32). Protein denaturation is the destruction of the secondary, tertiary and quaternary structures of a protein molecule under the influence of external factors. (Students write the definition in a notebook)
Slide 32. Protein denaturation. Factors causing denaturation: temperature, mechanical stress, action chemical substances and etc.
11. Virtual Lab (Slide 33-35). Watch the video of the film and discuss.
Slide 33. Experience number 1. Reversible protein denaturation. Saturated ammonium sulfate solution is added to the protein solution. The solution becomes cloudy. Protein denaturation has occurred. Protein precipitate in the test tube. This precipitate can be dissolved again if a few drops of a cloudy solution are added to water and the solution is stirred. The precipitate dissolves.
Slide 34. Experience number 2. Irreversible protein denaturation. Pour protein into a test tube and heat it to a boil. The clear solution becomes cloudy. Coagulated protein precipitates out. When proteins are exposed to high temperatures, irreversible protein coagulation occurs.
Slide 35. Experience number 3. Irreversible denaturation of protein by acids. Carefully add the protein solution to the test tube with nitric acid. A ring of coagulated protein appeared at the boundary of the two solutions. When shaking the tube, the amount of coagulated protein increased. Irreversible protein folding occurs.
12. Color reactions of proteins (Slide 36). Demonstration of experiments:
- biuret reaction.
- xantoprotein reaction.
- Qualitative determination of sulfur in proteins.
1) Biuret reaction. When proteins are exposed to a fresh precipitate of copper hydroxide in an alkaline medium, a violet color appears. Of the color reactions to proteins, the most characteristic is biuret, since the peptide bonds of proteins give a complex compound with copper (II) ions.
2) Xantoprotein reaction (interaction of aromatic cycles of radicals with concentrated nitric acid). When proteins are treated with concentrated nitric acid, a white precipitate is formed, which turns yellow when heated, and turns orange when a solution of ammonia is added.
3) Qualitative determination of sulfur in proteins. If lead acetate is added to a solution of proteins, and then sodium hydroxide and heated, a black precipitate forms, which indicates the sulfur content.
13. Hydrolysis of proteins (Slide 37-38). The types of protein hydrolysis students analyze and write down in a notebook.
Slide 37. Protein hydrolysis is one of the most important properties of proteins. Occurs in the presence of acids, bases or enzymes. For complete acid hydrolysis, it is necessary to boil the protein with hydrochloric acid for 12-70 hours. In the body, complete hydrolysis of proteins occurs under very mild conditions under the action of protolytic enzymes. It is important to draw students' attention to the fact that amino acids are the end product of protein hydrolysis.
Slide 38. Types of protein hydrolysis . Each type of organism, each organ and tissue contains its own characteristic proteins, and when digesting food proteins, the body breaks them down into individual amino acids, from which the body creates its own proteins. The breakdown of proteins is carried out in the digestive organs of humans and animals (stomach and small intestine) under the action of digestive enzymes: pepsin (in the acidic environment of the stomach) and trypsin, chemotrypsin, dipeptidase (in the slightly alkaline - pH 7.8 environment of the intestine). Hydrolysis is the basis of the digestion process. The human body should be supplied daily with food 60 – 80 g of protein. In the stomach, under the action of enzymes and hydrochloric acid, protein molecules break down into “bricks” – amino acids. Once in the blood, they are carried to all cells of the body, where they participate in the construction of their own protein molecules, characteristic only of this species.
14. Protein research in the 19th century (Slide 39-42). The discoveries of scientists - chemists F. Sanger, M.F. Peruts and D.K. Kendyr.
Slide 39. Scientists have completely determined the structure of some proteins: the hormone insulin, the antibiotic gramicidin, myoglobin, hemoglobin, etc.
Slide 40. In 1962 M.F. Peruts and D.K. Kendyryu were awarded the Nobel Prize for research in the field of protein research.
Slide 41. A hemoglobin molecule (Mr = (C 738 H 1166 O 208 S 2 Fe) = 68000) is built from four polypeptide chains (Mr = 17000 each). When combined with oxygen, the molecule changes its quaternary structure, capturing oxygen.
Slide 42. In 1954, F. Sanger deciphered the amino acid sequence in insulin (it was synthesized 10 years later). F. Sanger is an English biochemist. Since 1945, he began to study the natural protein insulin. This pancreatic hormone regulates the amount of glucose in the blood in the body. Violation of insulin synthesis leads to a failure of carbohydrate metabolism and a serious illness - diabetes mellitus. Using all the methods available to him and showing great skill, F. Sanger deciphered the structure of insulin. It turned out that it consists of two polypeptide chains with a length of 21 and 30 amino acid residues, interconnected in two places by disulfide bridges of cysteine fragments. The work took nine long years. In 1958, the scientist was awarded the Nobel Prize "for his work on the structure of proteins, especially insulin." Based on the discovery of F. Sanger in 1963, the first synthesis of insulin from individual amino acids was completed. It was a triumph for synthetic organic chemistry.
15. Functions of proteins (Slide 43). Independent work of students with the textbook Yu.I. Polyansky. General biology pp.43-46. Task for students: write down the functions of proteins in a notebook.
Slide 43. Checking and consolidating the completed task.
16. Proteins as a component of animal and human food (Slide 44-49). The nutritional value of proteins is determined by their content of essential amino acids.
Slide 44. With the complete breakdown of 1 gram of protein, 17.6 kJ of energy is released.
Student’s message on the topic: “Proteins are a source of essential amino acids in the body” (Appendix 4).
46 slide. Vegetable proteins are less valuable. They are poorer in lysine, methionine, tryptophan, and are more difficult to digest in the gastrointestinal tract.
During digestion, proteins are broken down into free amino acids, which, after being absorbed in the intestines, enter the bloodstream and are carried to all cells.
47 slide. Complete and incomplete proteins. Complete proteins are those that contain all the essential amino acids. Incomplete proteins do not contain all the essential amino acids.). Student's message on the topic - "The energy value of some products."(Annex 6).
17. The importance of proteins (Slide 48-49).
Slide 48. Proteins are an indispensable component of all living cells, they play an extremely important role in wildlife, they are the main, most valuable and indispensable component of nutrition. Proteins are the basis of structural elements and tissues, support metabolism and energy, participate in the processes of growth and reproduction, provide mechanisms for movement, the development of immune responses, and are necessary for the functioning of all organs and systems of the body.
Slide 49. We complete the study of the topic with the definition of life by F. Engels “Life is a way of existence of protein bodies, the essential point of which is the constant metabolism with the external nature surrounding them, and with the cessation of this metabolism, life also stops, which leads to the decomposition of the protein.”
IV. Analysis of homework: Chemistry. GE Rudzitis, pp. 158–162 to study the material.
V. Summing up the lesson.
Literature:
- Baranova T.A. Proper nutrition. – M.: Interbuk, 1991. – S. 78–80.
- Volkov V.A., Vonsky E.V., Kuznetsova G.I. Outstanding chemists of the world. – M.: VSh, 1991. 656 p.
- Gabrielyan O.S. Chemistry. Textbook 10 cells. for general education institutions - M .: Bustard, 2007.
- Gorkovenko M.Yu. Pourochnye development in chemistry. – M.: Vako, 2006. S. 270–274.
- Polyansky Yu.I. General biology. Textbook 10–11 grade. 2011
- Rudzitis G.E. Chemistry: Organic chemistry. Proc. 10 cells for general education institutions. - M .: Education, 2011 - pp. 158–162.
- Figurovsky N.A. Essay on the general history of chemistry. From ancient times to the beginning of the 19th century. – M.: Nauka, 1969. 455 p.
- Internet resources.
