Small molecules, their features and biological significance. What substances are protein monomers? What are protein monomers? What organic substances are they monomers of?

The purpose of the lesson: expand students' knowledge about natural high-molecular substances - proteins, study their structure, classification and properties.

Tasks:

• educational: formation of the concept of proteins based on structure and properties; consideration of their biological role; formation of general biological concepts;
• developing: development logical thinking students, general educational skills to compare, generalize knowledge on the topic “Proteins”; development of curiosity, cognitive interest in the topic under consideration;
• educational: formation of the scientific worldview of schoolchildren when studying the topic; environmental education; nurturing a caring attitude towards academic subject– biology.

New knowledge: organic substances that make up the cell; proteins; polymers; enzymes; antibodies; antigens.

Basic knowledge: inorganic substances that make up the cell; water; dipole; polarity; hydrolysis; mineral salts; buffering.

Form: lesson

Methods: explanatory and illustrative; reproductive, partially search.

Lesson type: lesson in learning new knowledge.

Equipment and materials: multimedia projector, presentation (by the author), test tasks.

During the classes

I. Organizational moment.

II. Updating students' sensory experience and basic knowledge.

- Guys, now I’ll ask you questions to see how you learned the material from the last lesson.

– What are carbohydrates? What is their content in animal and plant cells?

(Carbohydrates are organic substances with the general formula C n (H 2 O) m. Most carbohydrates have twice the number of water molecules than the number of carbon atoms, which is why they were called carbohydrates. In animal cell carbohydrates contain 1-2%, sometimes 5%, while in plant cells their content in some cases reaches 90% of dry weight (potato tubers, seeds, etc.)

– What functions do carbohydrates perform?

(Carbohydrates perform two main functions: construction and energy. For example, cellulose forms the walls of plant cells, etc. Carbohydrates play the role of the main source of energy in the cell. During the oxidation of 1 g of carbohydrates, 17.6 kJ of energy is released. Starch in plants and glycogen in animals, deposited in cells, they serve as a reserve of food and energy.)

– What are lipids? List the functions characteristic of them.

(Lipids are water-insoluble organic substances that are very diverse. The most common lipids found in nature are neutral fats. They are usually divided into fats and oils. Functions: 1) energy; 2) construction; 3) transport; 4) structural.)

- Guys, now do a little test:

I. Choose one correct answer.

Lipids dissolve in ether, but do not dissolve in water, since they
a) are polymers
b) consist of monomers
c) hydrophobic
d) hydrophilic

During their long winter sleep, bears obtain the water they need for life from
a) protein breakdown
b) melted snow
c) fat oxidation
d) oxidation of amino acids

The storage carbohydrate in an animal cell is
a) chitin
b) cellulose
c) starch
d) glycogen

II. Choose three correct answers out of six.

What carbohydrates are monosaccharides?
a) ribose
b) glucose
c) cellulose
d) fructose
e) starch
e) glycogen

Fats in the body of animals and humans
a) are broken down in the intestines
b) participate in the construction of cell membranes
c) are stored in the subcutaneous tissue, in the area of ​​the kidneys, heart
d) turn into proteins
d) are broken down in the intestines to glycerol and fatty acids
e) synthesized from amino acids

(Answers: 1 – c; 2 – c; 3 – d; 4 – a, b, d; 5 – b, c, e)

III. Motivation for schoolchildren's educational activities.

The teacher first reads the verse.

Changing your whimsical image every moment,
Capricious like a child and ghostly like smoke,
Everywhere life is boiling in fussy anxiety,
Mixing the great with the insignificant and ridiculous...

What is life? This question has always worried people. Over the centuries, observations have accumulated, research has been conducted, theories have been born and died. Perhaps no natural scientific phenomenon has caused such an acute struggle of worldviews as the problem of the living. And the reason for this struggle is in the object itself, its uniqueness, originality and complexity.
Gradually, enough experimental material was accumulated to give the following definition of life: “Life is a way of existence of protein bodies, the essential method of which is the constant exchange of substances with the external nature surrounding them, and with the cessation of this metabolism, life itself ceases, which leads to decomposition squirrel". (F. Engels).

Modern science presents life as an interweaving of complex chemical processes interactions between proteins and other substances. It should be emphasized that individual purified proteins do not have the characteristic features of life. Therefore, in search of an answer to the question “What is life?” you need to reveal the secret of the substances underlying it, that is, answer the question “What is protein?”

IV. Communicate the topic, purpose and objectives of the lesson.

Topic: Squirrels

Goal: To expand knowledge about natural high-molecular substances - proteins, to study their structure and properties.

V. Primary perception and awareness by students of new material.

Proteins are complex organic polymers whose monomers are amino acids. Natural proteins contain 20 amino acids, 8 of them are essential, i.e. are not synthesized in the body, so they must be taken into the body with food.

In the human body, there are 5 million types of protein molecules that differ not only from each other, but also from proteins of other organisms. Protein molecules can be helical, folded, or spherical.

For the first time he studied a protein molecule and found that it consists of amino acids - Ya.Beccori.

Proteins, in turn, have a complex structure. Distinguish primary, secondary, tertiary and quaternary structures protein molecule.

Primary structure– sequence of alternation of amino acid residues in a protein molecule (linear arrangement).

Secondary structure – twisting of the primary protein structure into a helix.

Tertiary structure– packaging of a twisted spiral into a ball-shaped configuration.

Quaternary structure – several tertiary structures (coils) combined into one.

Proteins perform following functions:

1) construction function– proteins are involved in the formation of all cell membranes and cell organelles, as well as extracellular structures.

2) catalytic function– accelerate reactions in the body.

3) motor function – special contractile proteins are involved in all types of movement that cells and organisms are capable of.

4) transport function – consists of the addition of chemical elements or biologically active substances and transferring them to various tissues and organs of the body.

5) protective function- special antibody proteins (formed in leukocytes) bind and neutralize substances unusual for the body - antigens.

6) energy function– when 1 g of protein is broken down, 17 kJ of energy is released.

I exist color reactions to proteins:

1) xanthoprotein reaction

2) biuret reaction

Also, proteins are characterized by a process called denaturation. Denaturation– disruption of the natural structure of the protein under the influence of heat or chemical reagents. Denatured protein loses its biological properties.

VI. Understanding internal patterns, connections between the subjects being studied in the process of mental work and performing cognitive tasks.

– Guys, here is a text that contains erroneous information. Your task is to identify mistakes made. At the same time, we do not forget that we work individually. (slide 18)

Proteins are complex organic polymers whose monomers are amino acids. Natural proteins contain 20 amino acids, 8 of them are essential, i.e. are synthesized in the body and their entry into the body not necessary along with food.
Proteins, interacting with nitric acid, give purple coloring. This reaction is called the xanthoprotein reaction. Secondary protein structure is an alternation of amino acids in a linear structure. Denaturation – process of changing the color of a protein molecule. Egg protein content less than in milk and dairy products. When cooking whites Not changes its color.

VII. Generalization and systematization of concepts studied in class and previously acquired knowledge.

– So, guys, after studying today’s topic, you can already perform a small test:

TEST to check:

What protein structure is twisted into a helix?
A) primary;
B) secondary;
B) tertiary;
D) quaternary.

How much energy is released when 1 g of protein is broken down?
A) 25 kJ;
B) 38 kJ;
B) 18 kJ;
D) 17 kJ.

What protein coloring does the biuret reaction produce?
A) purple;
B) green;
B) yellow;
D) 17 white.

How many essential amino acids are there?
A) 10;
B) 8;
IN 20;
D) 5.

What is denaturation?
A) disruption of the natural structure of the protein under the influence of heat or chemical reagents;
B) the process of changing the color of a protein molecule;
B) color reaction to proteins;
D) the process of restoring the natural structure of the protein.

The diversity of proteins is due to the various components they contain:
A) nucleotides;
B) amino acids;
B) lipids;
D) nucleic acids.

The quaternary structure of a protein molecule is formed as a result of the interaction:
A) sections of one protein molecule by type of bonds;
B) several polypeptide strands;
B) sections of one protein molecule due to hydrogen bonds;
D) a protein globule with a cell membrane.

The ability of protein molecules to combine with other substances and transport them in a cell or organism underlies the function:
A) transport;
B) catalytic;
B) signal;
D) energy.

What protein substances are synthesized in the body in response to the appearance of foreign bodies and substances in it?
A) carbohydrates;
B) enzymes;
B) antibodies;
D) hormones.

Enzymes perform the function:
A) structural;
B) catalytic;
B) contractile;
D) energy.

(Answers: 1. B; 2. G; 3. A; 4. B; 5. A; 6. B; 7. B; 8. A; 9. B; 10. B)

VIII. Summing up the lesson.

- Guys, our lesson is coming to an end. And I would like to hear the conclusion to our lesson today.

Conclusion: We expanded our knowledge about natural high-molecular substances - proteins, studied their structure and properties.

– Overall, the lesson went very well. You did a good job, showed activity and independence. Well done!

IX. Homework.

Questions 1-4 on page 112 (oral)

Create a crossword puzzle on the topic “Carbohydrates.” Lipids. Squirrels"

References:

1. Kamensky A.A. and others. Biology. Introduction to general biology and ecology. Textbook for 9th grade. 3rd ed., stereotype. – M.: Bustard, 2002. – 304 p.
2. Mamontov S.G. Biology. General patterns. 9th grade: Textbook. for general education institutions / S.G. Mamontov, V.B. Zakharov, N.I. Sonin. – 4th ed., stereotype. – M.: Bustard, 2003. – 288 p.: ill.
3. Ponomareva I.N., Kornilova O.A. Basics general biology. 9th grade: 2nd ed. – M.: Bustard, 2000.

Lesson-lecture “Molecular structure of living things”

Equipment: multimedia presentation.

I. Updating knowledge

Slide 1.“Key words (elementary composition of the cell, water, proteins, DNA, RNA, replication).”

Control test

1. Nucleic acids perform the following functions in the cell:

a) storage and transfer of hereditary properties;
b) control of protein synthesis;
c) regulation of biochemical processes;
d) cell division;
d) all of the above.

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2. Monomers of nucleic acids are:

a) amino acids;
b) nucleotides;
c) protein molecules;
d) glucose molecules.

3. Group of substances to which ribose belongs:

a) proteins;
b) fats;
c) carbohydrates.

4. The monomer of a protein molecule is:

a) glucose;
b) glycerin;
c) fatty acid;
d) amino acid.

5. Fat solvents can be:

a) water;
b) alcohol;
c) ether;
d) gasoline.

II. Learning new material

In science lessons, you touched upon the mystery of living things, trying to answer the question: “What is life?” We primarily associate the phenomenon of life with the substances from which living organisms are built: carbohydrates, fats, nucleic acids and, of course, proteins.

1. Elemental and molecular composition of living things

The human body contains 81 chemical elements out of 92 found in nature. ( Slide 2."Content of chemical elements in a cell." Human body- a complex chemical laboratory. It’s hard to imagine that our daily well-being, mood and even appetite can depend on minerals. Without them, vitamins are useless, the synthesis and breakdown of proteins, fats and carbohydrates is impossible.

On the students’ desks are tables “Biological role of chemical elements” (Table 1). After familiarizing themselves with it, students and the teacher analyze the table.

Table 1. Biological role of chemical elements

Chemical elements		Functional role
Potassium, sodium
	Calcium pectate
	Chlorophyll
	Nucleic acids, ATP
	Hemoglobin
	Cytochromes
Manganese	Decarboxylases, dehydrogenases
	Hemocyanin
	Tyrosinase
	Vitamin B 12
	Alcohol dehydrogenase
	Carbonic anhydrase
	Calcium fluoride
	Thyroxine
Molybdenum	Nitrogenase	Provides nitrogen fixation

The basis of life is made up of six elements of the first three periods - H, C, N, O, P, S. These elements are called biogenic, and they account for 98% of the mass of living matter (i.e., the remaining elements of the periodic table make up no more than 2% ).

Three main characteristics of nutrients:

– small atomic size,
– small relative atomic mass,
– the ability to form strong covalent bonds.

Texts are distributed to students. Exercise: read the text carefully; identify elements necessary for life and elements dangerous to living organisms; find them in the periodic table of elements and explain their role.

After completing the assignment, several students analyze different texts.

Text 1

The chemical element calcium is involved in the formation of bone tissue in animals and humans and in protein metabolism. Magnesium is part of plant chlorophyll and regulates blood pressure. It is necessary for the body to produce energy.

Barium is an element of the same subgroup; even in small quantities it is dangerous for the body. Barium salts are very poisonous. In acute poisoning, they affect the nervous system and blood vessels, and in chronic poisoning, they affect bone tissue, bone marrow, and liver. Barium displaces calcium and phosphorus from the bones - this leads to softening of the bones.

Text 2

An element of a secondary subgroup of group II, zinc is an essential microelement for living organisms. It is part of enzymes and hormones (for example, insulin produced by the pancreas). Zinc affects the growth of plants and animals (its deficiency causes dwarfism), is involved in anaerobic respiration of plants (alcoholic fermentation), and in transport carbon dioxide in the blood of vertebrates, in the absorption of proteins.

The content of cadmium and mercury in a living organism is minimal. Cadmium exhibits carcinogenic properties. Its soluble compounds, after absorption into the blood, affect the central nervous system, liver, and kidneys. This element enters the biosphere with mineral fertilizers (as an impurity in superphosphate) and when burning waste containing plastic products. A person who smokes one cigarette receives 1–2 mcg of cadmium into the lungs and 25% of this amount remains in the body.

Mercury ions in trace quantities are involved in the formation of proteins and the transfer of hereditary information. At the same time, in slightly larger doses they destroy protein molecules, cause nervous system disorders, impair heart function, inhibit the vital activity of phytoplankton (algae), etc.

Text 3

Boron - element main subgroup Group III is an essential microelement for the body (its content is 10–3%). This element has a positive effect on plant growth, respiration processes, and carbohydrate metabolism. Lack of boron leads to the death of plant growth points of stems and roots.

The concentrations of gallium and thallium in the human body are 10–6% and 10–12%, respectively. Thallium is a strong poison, its effect is manifested in neurological disorders and hair loss.

Text 4

Among the elements of group IV, carbon is the basis of life (its concentration in the human body is 10%), and lead (10–6–10–12%), and its compounds are poisons that cause cancer of the kidneys and gastrointestinal tract, interfering with gas exchange in fish (thicken the mucus covering the gills). The presence of lead in the natural environment is associated with its use in industry. The main use of lead in which it is widely dispersed is in the production and use of alkyl lead fuel additives. Large quantities of lead enter the soil and water with waste during the mining and processing of ores, the production of steel, batteries, typographic fonts, pigments, explosives, petroleum products, photographic materials, glass. To reduce lead emissions, they are switching to widespread use of electricity in transport, work is underway to reduce the lead content in motor gasoline and switch to alternative types of fuel. Internal combustion engines are being improved, new engine systems and electric vehicles are being created. Non-waste technologies are being introduced into the lead industry. Chronic lead poisoning primarily affects the functions of the central nervous system.

Text 5

Group V elements - nitrogen and phosphorus - are true biogens, i.e. are found in all organisms. Their content in the body is 0.1%. Their neighbor in the group - arsenic (10-6%) changes the thickness of the walls of blood vessels, causes cardiac disorders, dehydration of the body and loss of salts, disruption of oxygen transfer by hemoglobin in the blood (anemia develops). Arsenic poisoning increases the likelihood of skin cancer, diseases of the lymphatic system and gastrointestinal tract. It is assumed that arsenic replaces phosphorus in the DNA molecule in the body and disrupts the transmission of hereditary information. Arsenic compounds are contained in waste blast furnace gases, coal ash, and waste from copper smelting and sulfuric acid production.

2. The structure of the water molecule and its properties

(Students analyze the facts, remember the functions of water (Fig. 1), draw a conclusion about the correspondence between the water content and the intensity of the metabolic process.)

Rice. 1. Functions of water

Demonstration of experiments

1. Dissolve the following substances in water: table salt, ethyl alcohol, sucrose, vegetable oil.
2. Place a piece of ice in a glass of water.
3. Add gastric juice to the test tube with egg white flakes.

Answer the following questions:

Why do some substances dissolve in water while others do not?
What can you say about the density of water and ice?
What reactions did you observe in the experiment?
What properties of water have you observed?

(The teacher comments on the answers, students make notes in their notebooks.)

3. Amino acids and proteins

All organisms - fungi, plants, animals, bacteria - contain proteins.

Proteins are high-molecular organic substances built from residues of 20 different amino acids. More than 150 amino acids are known, but only 20 of them are present in proteins. Amino acids can exist in two isomeric forms, L and D, which are mirror images of each other. Proteins contain only L-isomers, and the inclusion of the D-isomer disrupts the protein structure.

Rice. 2. Levels of organization of the protein molecule

Proteins are the most important component of our food. In humans, proteins make up a quarter of body weight. The only source of their formation in the body is amino acids from proteins in food. This is why proteins are indispensable in human nutrition.

The molecular weight of proteins ranges from 5 thousand to 1 million and above. Only a small fraction of the theoretically possible amount of protein exists in nature.

Proteins are the basis of cell life. There are proteins in all parts of the body. In blood and muscles, proteins make up 1/5 of their total mass, in the brain 1/12, and in tooth enamel 1% of their total mass. In different organs, proteins make up 45–85% of the dry mass of the substance.

Proteins are formed by the polycondensation of α-amino acids, which creates a polypeptide bond. Therefore, proteins consist of the same elements as amino acids: carbon, hydrogen, nitrogen, oxygen and sulfur (Table 2).

Table 2. Elemental composition of proteins

Chemical elements	Substances that contain a chemical element	Functional role
Carbon, hydrogen, oxygen, nitrogen	Proteins, nucleic acids, lipids, carbohydrates and other organic substances	Required for synthesis organic matter and performing the functions performed by these organic substances
Potassium, sodium	Na + is the main extracellular ion, K + is the predominant ion inside cells	Provide membrane functions, conduction nerve impulses
		Participates in blood clotting and muscle contraction
	Calcium phosphate, calcium carbonate	Contains bone tissue, tooth enamel, and mollusk shells
	Calcium pectate	Participates in the formation of cell walls in plants
	Chlorophyll	Participates in the process of photosynthesis, activates enzymes
		Participates in the formation of the spatial structure of proteins
	Nucleic acids, ATP	Synthesis of nucleic acids (DNA, RNA); part of bones
		Participates in the conduction of nerve impulses
		Activates the work of digestive enzymes in gastric juice
	Hemoglobin	Transport of oxygen and carbon dioxide
	Cytochromes	Participates in the processes of photosynthesis and respiration
Manganese	Decarboxylases, dehydrogenases	Oxidation of fatty acids, participates in the processes of respiration and photosynthesis
	Hemocyanin	Provides oxygen transport in some invertebrates
	Tyrosinase	Participates in the synthesis of melanin – skin pigment
	Vitamin B 12	Necessary for the formation of erythrocytes (red blood cells)
	Alcohol dehydrogenase	Participates in glycolysis in yeast
	Carbonic anhydrase	Provides a balance of CO 2 and H 2 CO 3 in vertebrates, participates in pH regulation
	Calcium fluoride	Part of bone tissue and tooth enamel
	Thyroxine	Participates in the regulation of basal metabolism
Molybdenum	Nitrogenase	Provides nitrogen fixation

Laboratory work " Chemical composition cells"

To prove that proteins contain nitrogen, add an alkali solution to an aqueous solution of chicken egg white and heat it. We bring universal indicator paper moistened with water to the hole of the test tube - the paper turns blue, since ammonia gas NH 3 is released from the solution during alkaline hydrolysis of the protein. Therefore, protein contains nitrogen.

All proteins, plant and animal, are made up of amino acids. Proteins supplied with food are hydrolyzed under the influence of enzymes.

Hydrolysis- This is the decomposition of substances with the addition of water molecules. In the acidic environment of the stomach, under the action of proteolytic enzymes (enzymes that accelerate the hydrolysis of proteins), proteins are broken down into amino acids. Amino acids are absorbed by the intestinal villi, enter the blood, and with it into all tissues of the body. Then the bulk of the amino acids goes to the synthesis of the body’s own proteins.

Synthesis occurs with the absorption of energy. Such reactions are called endothermic. Some amino acids undergo breakdown and oxidation, while nitrogen is split off in the form of ammonia, which turns into urea and is excreted in the urine. Carbon and hydrogen are oxidized to carbon dioxide and water. These reactions release energy and are exothermic.

During protein metabolism, energy is exchanged. The synthesis of body proteins in the cell is accompanied by the absorption of energy (assimilation), and when proteins and amino acids are broken down, energy is released (dissimilation process).

4. Nucleotides and nucleic acids

There are two types of nucleic acids: DNA (deoxy ribonucleic acids), RNA (ribonucleic acids). 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.

Nucleotides consist of three components: a nitrogenous base, a pentose sugar, and a phosphoric acid residue. Nucleic acids contain five types of nitrogenous bases: adenine, guanine, uracil, thymine, cytosine. In addition to nitrogenous bases, two sugars take part in the formation of nucleotides: ribose in RNA and deoxyribose in DNA. The third component of nucleotides, both in DNA and RNA, is a phosphoric acid residue - phosphate.

The complex of a nitrogenous base with a sugar is called a nucleoside, and when a phosphate is added to the latter, a nucleotide is formed. The names of nucleotides are slightly different from the names of the corresponding bases. Both are usually denoted in capital letters:

cytosine, cytidine – C;
uracil, uridine – U;
adenine, adenosine – A;
thymine, thymidine – T;
guanine, guanosine – G.

DNA structure

DNA – deoxyribonucleic acid – is a high-molecular linear polymer consisting of two polynucleotide chains. Each of the DNA chains is a linear polymer in which the nucleotides are sequentially connected to each other using a covalent phosphodiester bond between the deoxyribose residue of one nucleotide and the phosphoric acid residue of another nucleotide (Fig. 3).

Rice. 3. DNA structure

DNA contains four types of nucleotides: A, T, G and C. In a DNA chain, nucleotides of the same type can be repeated countless times. DNA molecules can reach gigantic sizes. For example, 23 pairs of human chromosomes (consisting of DNA) contain more than 3 billion nucleotide pairs!

DNA in a cell is most often found in the form of a special structure - a double helix, in which the chains (DNA molecules) are tightly linked to each other. The existence of such a structure is possible due to the structural features of nucleotides, which easily form complementary pairs: T is always located opposite A, and G is always located opposite C. DNA chains are oriented in a strictly defined way: the nitrogenous bases of the nucleotides of both chains face inward, and sugars and phosphates face outward; in addition, the chains are located very close to each other (about 1.8 nm).

Between the nitrogenous 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.

Function of DNA is the storage, transmission and reproduction of genetic information over generations. In the body, DNA, being the basis for the uniqueness of the individual form, determines which proteins and in what quantities need to be synthesized.

DNA replication

The existence of a mechanism for “reproduction” of DNA molecules, thanks to which exact copies of the original molecules are reproduced, makes it possible to transfer genetic information from the mother cell to the daughter cells during division.

The process of doubling the number of DNA molecules is called replication. This is a complex process carried out by enzymes, the full name of which is DNA-dependent DNA polymerases type I, II, III (or simply DNA polymerases).

Replication is based on the ability of nucleotides to interact complementarily with the formation of hydrogen bonds between A and T, G and C.

Special proteins break the bonds between the strands and “unwind” the DNA molecule, so that its strands are separated. This unwinding occurs over a small segment of several tens of nucleotides. On the untwisted section, DNA polymerase builds daughter DNA strands. In this case, the mother chains act as templates on which enzymes, selecting complementary nucleotides one by one, build daughter chains. After the daughter DNA strands are built and complementarily connected to the mother ones, a new segment unwinds and the replication cycle repeats (Fig. 4).

This method of replication, in which double-stranded DNA is sent to each daughter cell, one strand of which is old, maternal, and the other newly synthesized, is called a semi-conservative method of DNA replication. The accuracy of information reproduction (the accuracy of the synthesis of daughter chains) during replication is almost absolute - the slightest mistake can lead to serious consequences. The biological meaning of replication lies in the accurate transfer of hereditary information from the mother molecule to the daughter, which occurs during the division of somatic cells.

However, errors occur here too, leading to spontaneous mutations. To increase the reliability of storing information in the cell, there are reparation systems, restoring a damaged DNA strand from an intact one. DNA repair is a mechanism that provides the ability to correct a broken nucleotide sequence in a DNA molecule. The change usually occurs in one of the DNA strands, while the other strand remains unchanged. All repair reactions are carried out by enzymes. The damaged section of the chain is “cut out” with the help of enzymes - DNA-repairing nucleases. Another enzyme, DNA polymerase, copies information from the undamaged strand, inserting the necessary nucleotides into the damaged strand. DNA ligase then “crosslinks” the DNA molecule and the damaged molecule is repaired.

RNA structure

Although the structure of RNA molecules is in many ways similar to the structure of DNA molecules, there are nevertheless a number of significant differences. RNA nucleotides contain the sugar ribose instead of deoxyribose, and uracil is used instead of thymine. The main difference between RNA and DNA is that RNA has only one strand. Because of this, RNA is chemically less stable than DNA, and RNA is quickly degraded in aqueous solutions. Therefore, RNA is less suitable for long-term storage of information.

There are three main types of RNA (Fig. 5). Messenger RNA – mRNA – is the most heterogeneous group of RNA molecules in size, structure and stability with a chain length of 75–3000 nucleotides. mRNA is a polynucleotide open chain. A single spatial structure characteristic of at least the majority of mRNAs has not been found. All mRNAs are united by their function - they serve as templates for protein synthesis (Fig. 7), transmitting information about their structure from DNA molecules.

Rice. 7. Protein synthesis scheme

Transport (acceptor) RNA - tRNA - consists of 75–100 nucleotides. The function of tRNA is the transfer of amino acids to the ribosome to the synthesized protein molecule. Number various types tRNA in the cell is small: 20–61. They all have a similar spatial organization.

Ribosomal RNA - rRNA - is a single-stranded nucleic acid, which, in combination with ribosomal proteins, forms ribosomes - organelles on which protein synthesis occurs (Fig. 6). There are many known types of rRNA - a heterogeneous group of molecules with a chain length of 120–3500 nucleotides. The cell contains most rRNA, much less tRNA and very little mRNA. Yes, in E. coli E.coli the ratio of these RNA species is approximately 82, 16 and 2%, respectively.

III. Consolidation

Filling out tables.

Comparative characteristics of DNA and RNA.

IV. Reflection. Summing up the lesson

V. Homework

Level 1. Answer the questions on p. 93 textbooks.

Level 2. Construct a spatial model of a small fragment of a DNA molecule using matches and plasticine balls.

Level 3. Collect additional material on the following topics: “Human Genome”, “Hereditary Diseases”, “Cloning of Animals”, “Human Genome in Medicine”, “History of the Discovery of Nucleic Acids”.

LITERATURE

1. Biology. Newspaper of the Publishing House “First of September”, 1998–2005.
2. Bogdanova T.G., Solodova E.A. Handbook for high school students and applicants to universities. – M.: Ast-Press, 2003.
3. Disk 1C: Tutor. Biology. – M., 2002.
4. Disc “Encyclopedia of Cyril and Methodius”. – M., 2004.
5. Zakiev R.K. Selected chapters of general genetics. – Kazan, 1991.
6. Kiseleva Z.S., Myagkova A.N. Genetics . – M.: Education, 1983.
7. Mamontov S.G. Biology. – M.: School-press, 1994.
8. Pavlov I.Yu., Vakhnenko D.V., Moskvichev D.V. Biology, tutor for admission to universities. – Rostov-on-Don, 2002.
9. Robert I.V. Modern educational technology. – M.: School-press, 1994.
10. Sapin M.R., Bilich G.L. Human anatomy. – M.: graduate School, 1989.
11. Selevko G.K. Modern educational technologies. – M.: Public Education, 1998.
12. Frank-Kamenetsky M.D. The most important molecule. – M.: Nauka, 1988.
13. Sherstnev M.P., Komarov O.S. Chemistry and biology of nucleic acids. – M.: Education, 1990.
14. Schlegel G. General microbiology. – M.: Mir, 1987.

Organic substances. Concept of biopolymers. As already noted, living organisms, in addition to inorganic ones, include various organic substances: proteins, lipids, carbohydrates, nucleic acids, etc. They are formed primarily by four chemical elements: carbon, hydrogen, oxygen and nitrogen. In proteins, sulfur is added to these elements, and in nucleic acids, phosphorus is added.

In living organisms, organic substances are represented by both small molecules with a relatively low molecular weight and macromolecules. TO low molecular weight compounds include amino acids, monosaccharides, nucleotides, carboxylic acids, alcohols and some others. Macromolecules(from Greek macro- large) are represented by proteins, polysaccharides and nucleic acids. These are structurally complex compounds with a large molecular weight. Yes, relative molecular mass most proteins range from 5000 to 1,000,000. As you know from your chemistry course, relative molecular weight (R4G) is equal to the ratio of the mass of one molecule of a substance to part of the mass of a carbon atom and, therefore, is a dimensionless quantity. The value of L4 G shows how many times the mass of a molecule of a given substance is greater than the atomic mass unit.

Molecules of proteins, polysaccharides and nucleic acids consist of large number repeating units of identical or different composition. As you know from your chemistry course, such compounds are called polymers. The simple molecules from which polymers are made are called monomers. The monomers of proteins are amino acids, the monomers of polysaccharides are monosaccharides, and nucleic acid molecules are built from nucleotides. Proteins, polysaccharides and nucleic acids are found in the cells of all living organisms and perform extremely important functions. biological functions, that's why they are called biological polymers (biopolymers).

In the cells of different living organisms the content of certain organic compounds is different. For example, proteins and lipids predominate in animal cells, while carbohydrates predominate in plant cells. However, in different cells certain organic compounds perform similar functions.

In living organisms among macromolecules functional significance the leading role belongs to proteins. Proteins are predominant and quantitative in many organisms. Thus, in the body of animals they make up 40-50%, in the body of plants - 20-35% of dry mass. Proteins are polymers whose monomers are amino acids.

Amino acids - "building blocks" of protein molecules. Amino acids are organic compounds containing both an amino group (-NH 2), which is characterized by basic properties, and a carboxyl group (-COOH) with acidic properties. About 200 amino acids are known, but only 20 are involved in the formation of natural proteins. Such amino acids are called protein-forming amino acids. Table 2 shows the full and abbreviated names of these amino acids (not for memorization).

Table 2. Protein-forming amino acids and their abbreviations

In protein-forming amino acid molecules, the carboxyl group and the amino group are bonded to the same carbon atom. According to this feature, 20 amino acids are similar to each other. The other part of the molecule, called the radical (R), has a different structure for different amino acids (Fig. 6). The radical can be nonpolar or polar, hydrophobic or hydrophilic, which gives different amino acids special properties.

Most protein-forming amino acids have one carboxyl group and one amino group - such amino acids are called neutral (see Fig. 6). There are also basic amino acids, with more than one amino group, and acidic amino acids, with more than one carboxyl group. The presence of an additional amino or carboxyl group affects the properties of the amino acid, which play a decisive role in the formation of the spatial structure of the protein. The radical of some amino acids (for example, cysteine) contains sulfur atoms.

Autotrophic organisms synthesize all the amino acids they need from the primary products of photosynthesis and nitrogen-containing inorganic compounds. For heterotrophic organisms The source of amino acids is food. In the human and animal body, some amino acids can be synthesized from metabolic products (primarily from other amino acids). Such amino acids are called nonessential. Others, the so-called essential amino acids, cannot be synthesized in the body and therefore must constantly be supplied to it as part of food proteins. Food proteins that contain residues of all essential amino acids are called complete, in contrast to incomplete proteins, which do not contain residues of certain essential amino acids.

Essential amino acids for humans are: tryptophan, lysine, valine, isoleucine, threonine, phenylalanine, methionine and leucine. Arginine and histidine are also essential for children.

The presence of both basic and acidic groups determines amphotericity and high reactivity amino acids. The amino group (-NH 2) of one amino acid is capable of interacting with the carboxyl group (-COOH) of another amino acid. In this case, a water molecule is released, and a covalent bond appears between the nitrogen atom of the amino group and the carbon atom of the carboxyl group, which is called peptide bond. The resulting molecule is dipeptide(Fig. 7). At one end of the dipeptide molecule there is a free amino group, and at the other there is a free carboxyl group. Thanks to this, the dipeptide can attach other amino acids to itself, forming oligopeptides. If more than one is connected in this way 10 amino acid residues, then it is formed polypeptide.

Peptides play an important role in the human body. Many hormones (glucagon, vasopressin, oksitotsin, etc.), antibiotics (for example, gramicidin), toxins (for example, diphtheria toxin) are oligo- and polypeptides by chemical nature.

Squirrels. Levels of organization of a protein molecule. Polypeptide chains can be very long and contain a wide variety of combinations of amino acid residues. Polypeptides whose molecules contain from 50 to several thousand amino acid residues are called proteins. Each specific protein is characterized strictly permanent staff and the sequence of amino acid residues.

Proteins formed only by amino acid residues are called simple. Complex proteins are those that contain a non-amino acid component. These can be metal ions (Fe 2+, Zn 2+, Mg 2 ^ Mn 2+), lipids, nucleotides, sugars, etc. Simple proteins are blood albumin, fibrin, some enzymes (trypsin), etc. Complex proteins are most enzymes, immunoglobulins (antibodies).

Protein molecules can take on different spatial forms, which represent four levels of their structural organization (Fig. 8).

A chain of many amino acid residues connected by peptide bonds is primary structure protein molecule. This is the most important structure, as it determines the shape, properties and functions of the protein. Based on the primary structure, other types of structures are created. Each protein in the body has a unique primary structure.

Secondary structure protein arises as a result of the formation of hydrogen bonds between the hydrogen atoms of NH groups and the oxygen atoms of CO groups of different amino acid residues of the polypeptide chain. The polypeptide chain is twisted into a spiral. Hydrogen bonds are weak, but due to their significant number they ensure the stability of this structure. For example, the molecules of keratin, the main protein of human hair and nails, have a completely spiral configuration. Helical secondary structure is also characteristic of some other proteins, for example myosin

The secondary structure of the protein, in addition to the helix, can be represented by a folded layer. In this case, several polypeptide chains (or sections of one polypeptide chain) are placed in parallel, forming a structure folded like an accordion (see Fig. 8). For example, the protein fibroin, which forms the basis of natural silk fibers, has this configuration.

Tertiary structure is formed due to the formation of hydrogen, ionic and other bonds that arise between different groups of atoms of a protein molecule in an aqueous environment. In some proteins, S - S bonds (disulfide bonds) between cysteine ​​residues (an amino acid containing sulfur) play an important role in the formation of the tertiary structure. In this case, the polypeptide helix fits into a kind of ball (globule) in such a way that hydrophobic amino acid radicals are immersed inside the globule, and hydrophilic ones are located on the surface and interact with water molecules. The tertiary structure determines the specificity of protein molecules and their biological activity. Many proteins have a tertiary structure, such as myoglobin (a protein that is involved in creating oxygen reserves in the muscles) and trypsin (an enzyme that breaks down food proteins in the intestines).

Some protein molecules contain not one, but several polypeptides that form a single complex. This is how it is formed quaternary structure. Polypeptides (they may have the same or different structures) do not bind covalent bonds. The strength of the quaternary structure is ensured by the interaction of weak intermolecular forces. For example, the quaternary structure is characteristic of the hemoglobin protein. Its molecule consists of four structural elements - subunits, each subunit includes a polypeptide chain and a non-protein component - heme.

55. What substances are synthesized in human cells from amino acids
A) phospholipids B) carbohydrates C) vitamins D) proteins

81. Amino acids are monomers of molecules of which organic substances?
A) proteins B) carbohydrates C) DNA D) lipids

109. The formation of peptide bonds between amino acids in a protein molecule is based on
A) the principle of complementarity
B) insolubility of amino acids in water
B) solubility of amino acids in water
D) the presence of carboxyl and amine groups in them

163. The enzymatic function in the cell is performed
A) proteins
B) lipids
B) carbohydrates
D) nucleic acids

250. The synthesis of what simple organic substances in the laboratory confirmed the possibility of the abiogenic origin of proteins
A) amino acids
B) sugars
B) fats
D) fatty acids

364. Name a molecule that is part of a cell and has carboxyl and amino groups
A) Glucose
B) DNA
B) Amino acid
D) Fiber

439. Hydrogen bonds between CO and NH groups in a protein molecule give it a spiral shape, characteristic of the structure
A) primary
B) secondary
B) tertiary
D) quaternary

490. The secondary structure of a protein, shaped like a helix, is held together by bonds
A) peptide
B) ionic
B) hydrogen
D) covalent

550. Organic substances that accelerate metabolic processes -
A) amino acids
B) monosaccharides
B) enzymes
D) lipids

945. What bonds determine the primary structure of protein molecules
A) hydrophobic between amino acid radicals
B) hydrogen between polypeptide strands
B) peptide between amino acids
D) hydrogen between -NH- and -CO- groups

984. The process of denaturation of a protein molecule is reversible if the bonds are not broken
A) hydrogen
B) peptide
B) hydrophobic
D) disulfide

1075. The quaternary structure of a protein molecule is formed as a result of interaction
A) sections of one protein molecule by type S-S connections
B) several polypeptide strands forming a ball
B) sections of one protein molecule due to hydrogen bonds
D) protein globule with cell membrane

1290. The secondary structure of a protein molecule has the form
A) spirals
B) double helix
B) ball
D) threads

1291. What is the function of proteins produced in the body when bacteria or viruses penetrate it?
A) regulatory
B) signal
B) protective
D) enzymatic

1293. What is the function of proteins that accelerate chemical reactions in a cell?
A) hormonal
B) signal
B) enzymatic
D) informational

1312. Accelerate chemical reactions in the cell
A) enzymes
B) pigments
B) vitamins
D) hormones

2063. The primary structure of a protein is formed by a bond
A) hydrogen
B) macroergic
B) peptide
D) ionic

2065. The main function of enzymes in the body
A) catalytic
B) protective
B) storing
D) transport

2088. By their nature, enzymes belong to
A) nucleic acids
B) proteins
B) lipids
D) carbohydrates

2144. Destruction of the structure of a protein molecule is
A) denaturation
B) broadcast
B) reduplication
D) renaturation

2367. Speed chemical reactions in the cell they change proteins that perform the function
A) signal
B) humoral
B) catalytic
D) informational

2420. Biocatalysts of chemical reactions in the human body are
A) hormones
B) carbohydrates
B) enzymes
D) vitamins

2483. The protective function in the body is performed by proteins that
A) carry out immune reactions
B) capable of contraction
C) carry out oxygen transport
D) speed up metabolic reactions

2504. The sequence and number of amino acids in a polypeptide chain is
A) primary structure of DNA
B) primary structure of the protein
B) secondary structure of DNA
D) protein secondary structure

2562. Enzymatic, construction, transport, protective functions in the cell are performed by molecules
A) lipids
B) carbohydrates
B) DNA
D) proteins

Proteins are biological polymers with a complex structure. They have a high molecular weight and consist of amino acids, prosthetic groups represented by vitamins, lipid and carbohydrate inclusions. Proteins containing carbohydrates, vitamins, metals or lipids are called complex proteins. Simple proteins consist only of amino acids linked together by peptide bonds.

Peptides

Regardless of what structure the substance has, the monomers of proteins are amino acids. They form a basic polypeptide chain, from which the fibrillar or globular structure of the protein is then formed. In this case, protein can only be synthesized in living tissue - in plant, bacterial, fungal, animal and other cells.

The only organisms that cannot join protein monomers are viruses and protozoan bacteria. All others are capable of forming structural proteins. But what substances are protein monomers, and how are they formed? Read about this and about polypeptides and structure formation, about amino acids and their properties below.

The only monomer of a protein molecule is any alpha amino acid. In this case, a protein is a polypeptide, a chain of connected amino acids. Depending on the number of amino acids involved in its formation, dipeptides (2 residues), tripeptides (3), oligopeptides (contains 2-10 amino acids) and polypeptides (many amino acids) are distinguished.

Protein structure overview

The structure of a protein can be primary, a little more complex - secondary, even more complex - tertiary, and the most complex - quaternary.

The primary structure is a simple chain in which protein monomers (amino acids) are connected through a peptide bond (CO-NH). The secondary structure is an alpha helix or beta fold. Tertiary is an even more complicated three-dimensional protein structure, which was formed from the secondary due to the formation of covalent, ionic and hydrogen bonds, as well as hydrophobic interactions.

The quaternary structure is the most complex and is characteristic of receptor proteins located on cell membranes. This is a supramolecular (domain) structure formed by the combination of several molecules with a tertiary structure, supplemented with carbohydrate, lipid or vitamin groups. In this case, as with the primary, secondary and tertiary structures, the monomers of proteins are alpha amino acids. They are also connected by peptide bonds. The only difference is the complexity of the structure.

Amino acids

The only monomers of protein molecules are alpha amino acids. There are only 20 of them, and they are almost the basis of life. Thanks to the advent of the peptide bond, it became possible. And the protein itself then began to perform structure-forming, receptor, enzymatic, transport, mediator and other functions. Thanks to this, a living organism functions and is able to reproduce.

The alpha amino acid itself is an organic carboxylic acid with an amino group attached to the alpha carbon atom. The latter is located next to the carboxyl group. In this case, protein monomers are considered as those whose terminal carbon atom carries both an amine and a carboxyl group.

Compounding amino acids in peptides and proteins

Amino acids combine into dimers, trimers and polymers through peptide bonds. It is formed by the elimination of a hydroxyl (-OH) group from the carboxyl site of one alpha amino acid and a hydrogen (-H) from the amino group of another alpha amino acid. As a result of the interaction, water is eliminated, and at the carboxyl end there remains a C=O region with a free electron near the carbon of the carboxyl residue. In the amino group of another acid there is a residue (NH) with an existing nitrogen atom. This allows two radicals to combine to form a bond (CONH). It's called peptide.

Alpha Amino Acid Variations

There are a total of 23 known alpha amino acids. They are presented in the form of a list: glycine, valine, alanine, isolecine, leucine, glutamate, asparaginate, ornithine, threonine, serine, lysine, cystine, cysteine, phenylalanine, methionine, tyrosine, proline, tryptophan, hydroxyproline, arginine, histidine, asparagine and glutamine. Depending on whether they can be synthesized by the human body, these amino acids are divided into non-essential and essential.

The concept of nonessential and essential amino acids

The human body can synthesize replaceable ones, while essential ones must come only from food. At the same time, both essential and non-essential acids are important for protein biosynthesis, because without them the synthesis cannot be completed. Without one amino acid, even if all the others are present, it is impossible to build exactly the protein that the cell requires to perform its functions.

One mistake at any stage of biosynthesis - and the protein is no longer suitable, because it will not be able to assemble into the desired structure due to a violation of electron densities and interatomic interactions. Therefore, it is important for humans (and other organisms) to consume essential amino acids. Their absence in food leads to a number of protein metabolism disorders.

Process of peptide bond formation

The only monomers of proteins are alpha amino acids. They are gradually connected into a polypeptide chain, the structure of which is pre-stored in genetic code DNA (or RNA if bacterial biosynthesis is considered). In this case, a protein is a strict sequence of amino acid residues. This is a chain, ordered into a specific structure, performing a pre-programmed function in the cell.

Stage sequence of protein biosynthesis

The process of protein formation consists of a chain of stages: replication of a section of DNA (or RNA), synthesis of information-type RNA, its release into the cytoplasm of the cell from the nucleus, connection with the ribosome and gradual attachment of amino acid residues that are supplied by transfer RNA. The substance, which is a protein monomer, participates in the enzymatic reaction of removing the hydroxyl group and a hydrogen proton, and then attaches to the growing polypeptide chain.

In this way, a polypeptide chain is obtained, which, already in the cellular endoplasmic reticulum, is ordered into a certain predetermined structure and is supplemented with a carbohydrate or lipid residue, if required. This is called the process of “maturation” of the protein, after which it is sent by the cellular transport system to its destination.

Functions of synthesized proteins

Protein monomers are amino acids necessary to build their primary structure. The secondary, tertiary and quaternary structure is already formed on its own, although sometimes it also requires the participation of enzymes and other substances. However, they are no longer essential, although they are essential for proteins to perform their function.

An amino acid, which is a protein monomer, can have attachment sites for carbohydrates, metals or vitamins. The formation of a tertiary or quaternary structure makes it possible to find even more places for the location of insertion groups. This makes it possible to create a derivative from a protein that plays the role of an enzyme, a receptor, a carrier of substances into or out of a cell, an immunoglobulin, a structural component of a membrane or cellular organelle, or a muscle protein.

Proteins, made from amino acids, are the only basis of life. And today it is believed that life just arose after the appearance of the amino acid and as a result of its polymerization. After all, it is the intermolecular interaction of proteins that is the beginning of life, including intelligent life. All other biochemical processes, including energy ones, are needed for implementation protein biosynthesis, and as a result, the further continuation of life.