TO nucleic acids include high-polymer compounds that decompose during hydrolysis into purine and pyrimidine bases, pentose and phosphoric acid. Nucleic acids contain carbon, hydrogen, phosphorus, oxygen and nitrogen. There are two classes of nucleic acids: ribonucleic acids (RNA) And deoxyribonucleic acids (DNA).

Structure and functions of DNA

DNA- a polymer whose monomers are deoxyribonucleotides. The model of the spatial structure of the DNA molecule in the form of a double helix was proposed in 1953 by J. Watson and F. Crick (to build this model, they used the work of M. Wilkins, R. Franklin, E. Chargaff).

DNA molecule formed by two polynucleotide chains, spirally twisted around each other and together around an imaginary axis, i.e. is a double helix (exception - some DNA-containing viruses have single-stranded DNA). The diameter of the DNA double helix is 2 nm, the distance between adjacent nucleotides is 0.34 nm, and there are 10 pairs of nucleotides per turn of the helix. The length of the molecule can reach several centimeters. Molecular weight - tens and hundreds of millions. The total length of DNA in the human cell nucleus is about 2 m. In eukaryotic cells, DNA forms complexes with proteins and has a specific spatial conformation.

DNA monomer - nucleotide (deoxyribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of nucleic acids belong to the classes of pyrimidines and purines. Pyrimidine bases of DNA(have one ring in their molecule) - thymine, cytosine. Purine bases(have two rings) - adenine and guanine.

The monosaccharide of the DNA nucleotide is represented by deoxyribose.

The name of the nucleotide is derived from the name of the corresponding base. Nucleotides and nitrogenous bases are indicated by capital letters.

A polynucleotide chain is formed as a result of nucleotide condensation reactions. In this case, between the 3 "-carbon of the deoxyribose residue of one nucleotide and the phosphoric acid residue of the other, phosphoether bond(belongs to the category of strong covalent bonds). One end of the polynucleotide chain ends with a 5 "carbon (it is called the 5" end), the other ends with a 3 "carbon (3" end).

Against one chain of nucleotides is a second chain. The arrangement of nucleotides in these two chains is not random, but strictly defined: thymine is always located opposite the adenine of one chain in the other chain, and cytosine is always located opposite guanine, two hydrogen bonds arise between adenine and thymine, three hydrogen bonds between guanine and cytosine. The pattern according to which the nucleotides of different strands of DNA are strictly ordered (adenine - thymine, guanine - cytosine) and selectively combine with each other is called the principle of complementarity. It should be noted that J. Watson and F. Crick came to understand the principle of complementarity after reading the works of E. Chargaff. E. Chargaff, having studied a huge number of samples of tissues and organs of various organisms, found that in any DNA fragment the content of guanine residues always exactly corresponds to the content of cytosine, and adenine to thymine ( "Chargaff's rule"), but he could not explain this fact.

From the principle of complementarity, it follows that the nucleotide sequence of one chain determines the nucleotide sequence of another.

DNA strands are antiparallel (opposite), i.e. nucleotides of different chains are located in opposite directions, and, therefore, opposite the 3 "end of one chain is the 5" end of the other. The DNA molecule is sometimes compared to a spiral staircase. The "railing" of this ladder is the sugar-phosphate backbone (alternating residues of deoxyribose and phosphoric acid); "steps" are complementary nitrogenous bases.

Function of DNA- storage and transmission of hereditary information.

Replication (reduplication) of DNA

- the process of self-doubling, the main property of the DNA molecule. Replication belongs to the category of reactions matrix synthesis, comes with the participation of enzymes. Under the action of enzymes, the DNA molecule unwinds, and around each strand acting as a template, a new strand is completed according to the principles of complementarity and antiparallelism. Thus, in each daughter DNA, one strand is the parent strand, and the second strand is newly synthesized. This kind of synthesis is called semi-conservative.

The "building material" and source of energy for replication are deoxyribonucleoside triphosphates(ATP, TTP, GTP, CTP) containing three phosphoric acid residues. When deoxyribonucleoside triphosphates are included in the polynucleotide chain, two terminal residues of phosphoric acid are cleaved off, and the released energy is used to form a phosphodiester bond between nucleotides.

The following enzymes are involved in replication:

helicases ("unwind" DNA);
destabilizing proteins;
DNA topoisomerases (cut DNA);
DNA polymerases (select deoxyribonucleoside triphosphates and complementarily attach them to the DNA template chain);
RNA primases (form RNA primers, primers);
DNA ligases (sew DNA fragments together).

With the help of helicases, DNA is untwisted in certain regions, single-stranded DNA regions are bound by destabilizing proteins, and replication fork. With a discrepancy of 10 pairs of nucleotides (one turn of the helix), the DNA molecule must complete a complete revolution around its axis. To prevent this rotation, DNA topoisomerase cuts one DNA strand, allowing it to rotate around the second strand.

DNA polymerase can only attach a nucleotide to the 3"-carbon of the deoxyribose of the previous nucleotide, so this enzyme is able to move along template DNA in only one direction: from the 3" end to the 5" end of this template DNA. Since the chains in maternal DNA are antiparallel , then on its different chains the assembly of daughter polynucleotide chains occurs in different ways and in opposite directions. On the 3 "-5" chain, the synthesis of the daughter polynucleotide chain proceeds without interruption; this daughter chain will be called leading. On the chain 5 "-3" - intermittently, in fragments ( fragments of Okazaki), which, after completion of replication by DNA ligases, are fused into one strand; this child chain will be called lagging (lagging behind).

A feature of DNA polymerase is that it can start its work only with "seeds" (primer). The role of "seeds" is performed by short RNA sequences formed with the participation of the RNA primase enzyme and paired with template DNA. RNA primers are removed after the completion of the assembly of polynucleotide chains.

Replication proceeds similarly in prokaryotes and eukaryotes. The rate of DNA synthesis in prokaryotes is an order of magnitude higher (1000 nucleotides per second) than in eukaryotes (100 nucleotides per second). Replication begins simultaneously in several regions of the DNA molecule. A piece of DNA from one origin of replication to another forms a unit of replication - replicon.

Replication occurs before cell division. Thanks to this ability of DNA, the transfer of hereditary information from the mother cell to the daughter cells is carried out.

Reparation ("repair")

reparations is the process of repairing damage to the nucleotide sequence of DNA. It is carried out by special enzyme systems of the cell ( repair enzymes). The following stages can be distinguished in the process of DNA structure repair: 1) DNA-repairing nucleases recognize and remove the damaged area, resulting in a gap in the DNA chain; 2) DNA polymerase fills this gap by copying information from the second (“good”) strand; 3) DNA ligase “crosslinks” the nucleotides, completing the repair.

Three repair mechanisms have been studied the most: 1) photoreparation, 2) excise or pre-replicative repair, 3) post-replicative repair.

Changes in the structure of DNA occur constantly in the cell under the influence of reactive metabolites, ultraviolet radiation, heavy metals and their salts, etc. Therefore, defects in repair systems increase the rate of mutation processes, are the cause hereditary diseases(pigment xeroderma, progeria, etc.).

Structure and functions of RNA

is a polymer whose monomers are ribonucleotides. Unlike DNA, RNA is formed not by two, but by one polynucleotide chain (exception - some RNA-containing viruses have double-stranded RNA). RNA nucleotides are capable of forming hydrogen bonds with each other. RNA chains are much shorter than DNA chains.

RNA monomer - nucleotide (ribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of RNA also belong to the classes of pyrimidines and purines.

The pyrimidine bases of RNA are uracil, cytosine, and the purine bases are adenine and guanine. The RNA nucleotide monosaccharide is represented by ribose.

Allocate three types of RNA: 1) informational(matrix) RNA - mRNA (mRNA), 2) transport RNA - tRNA, 3) ribosomal RNA - rRNA.

All types of RNA are unbranched polynucleotides, have a specific spatial conformation and take part in the processes of protein synthesis. Information about the structure of all types of RNA is stored in DNA. The process of RNA synthesis on a DNA template is called transcription.

Transfer RNAs usually contain 76 (from 75 to 95) nucleotides; molecular weight - 25,000-30,000. The share of tRNA accounts for about 10% of the total RNA content in the cell. tRNA functions: 1) transport of amino acids to the site of protein synthesis, to ribosomes, 2) translational mediator. About 40 types of tRNA are found in the cell, each of them has a nucleotide sequence characteristic only for it. However, all tRNAs have several intramolecular complementary regions, due to which tRNAs acquire a conformation that resembles a clover leaf in shape. Any tRNA has a loop for contact with the ribosome (1), an anticodon loop (2), a loop for contact with the enzyme (3), an acceptor stem (4), and an anticodon (5). The amino acid is attached to the 3' end of the acceptor stem. Anticodon- three nucleotides that "recognize" the mRNA codon. It should be emphasized that a particular tRNA can transport a strictly defined amino acid corresponding to its anticodon. The specificity of the connection of amino acids and tRNA is achieved due to the properties of the enzyme aminoacyl-tRNA synthetase.

Ribosomal RNA contain 3000-5000 nucleotides; molecular weight - 1,000,000-1,500,000. rRNA accounts for 80-85% of the total RNA content in the cell. In combination with ribosomal proteins, rRNA forms ribosomes - organelles that carry out protein synthesis. In eukaryotic cells, rRNA synthesis occurs in the nucleolus. rRNA functions: 1) a necessary structural component of ribosomes and, thus, ensuring the functioning of ribosomes; 2) ensuring the interaction of the ribosome and tRNA; 3) initial binding of the ribosome and the mRNA initiator codon and determination of the reading frame, 4) formation of the active center of the ribosome.

Information RNA varied in nucleotide content and molecular weight (from 50,000 to 4,000,000). The share of mRNA accounts for up to 5% of the total RNA content in the cell. Functions of mRNA: 1) transfer of genetic information from DNA to ribosomes, 2) a matrix for the synthesis of a protein molecule, 3) determination of the amino acid sequence of the primary structure of a protein molecule.

The structure and functions of ATP

Adenosine triphosphoric acid (ATP) is a universal source and main accumulator of energy in living cells. ATP is found in all plant and animal cells. The amount of ATP averages 0.04% (of the raw mass of the cell), the largest amount of ATP (0.2-0.5%) is found in skeletal muscles.

ATP consists of residues: 1) a nitrogenous base (adenine), 2) a monosaccharide (ribose), 3) three phosphoric acids. Since ATP contains not one, but three residues of phosphoric acid, it belongs to ribonucleoside triphosphates.

For most types of work occurring in cells, the energy of ATP hydrolysis is used. At the same time, when the terminal residue of phosphoric acid is cleaved, ATP is converted into ADP (adenosine diphosphoric acid), when the second phosphoric acid residue is cleaved, it becomes AMP (adenosine monophosphoric acid). The yield of free energy during the elimination of both the terminal and the second residues of phosphoric acid is 30.6 kJ each. Cleavage of the third phosphate group is accompanied by the release of only 13.8 kJ. The bonds between the terminal and the second, second and first residues of phosphoric acid are called macroergic (high-energy).

ATP reserves are constantly replenished. In the cells of all organisms, ATP synthesis occurs in the process of phosphorylation, i.e. addition of phosphoric acid to ADP. Phosphorylation occurs with different intensity during respiration (mitochondria), glycolysis (cytoplasm), photosynthesis (chloroplasts).

ATP is the main link between processes accompanied by the release and accumulation of energy, and processes that require energy. In addition, ATP, along with other ribonucleoside triphosphates (GTP, CTP, UTP), is a substrate for RNA synthesis.

Go to lectures №3“The structure and function of proteins. Enzymes»

Go to lectures number 5"Cell Theory. Types of cellular organization»

Structure and functions of DNA

The monosaccharide of the DNA nucleotide is represented by deoxyribose.

The name of the nucleotide is derived from the name of the corresponding base. Nucleotides and nitrogenous bases are indicated by capital letters.

From the principle of complementarity, it follows that the nucleotide sequence of one chain determines the nucleotide sequence of another.

Function of DNA- storage and transmission of hereditary information.

Replication (reduplication) of DNA

- the process of self-doubling, the main property of the DNA molecule. Replication belongs to the category of matrix synthesis reactions and involves enzymes. Under the action of enzymes, the DNA molecule unwinds, and around each strand acting as a template, a new strand is completed according to the principles of complementarity and antiparallelism. Thus, in each daughter DNA, one strand is the parent strand, and the second strand is newly synthesized. This kind of synthesis is called semi-conservative.

The following enzymes are involved in replication:

helicases ("unwind" DNA);
destabilizing proteins;
DNA topoisomerases (cut DNA);
DNA polymerases (select deoxyribonucleoside triphosphates and complementarily attach them to the DNA template chain);
RNA primases (form RNA primers, primers);
DNA ligases (sew DNA fragments together).

Replication occurs before cell division. Thanks to this ability of DNA, the transfer of hereditary information from the mother cell to the daughter cells is carried out.

Reparation ("repair")

Three repair mechanisms have been studied the most: 1) photoreparation, 2) excise or pre-replicative repair, 3) post-replicative repair.

Changes in the structure of DNA occur constantly in the cell under the influence of reactive metabolites, ultraviolet radiation, heavy metals and their salts, etc. Therefore, defects in repair systems increase the rate of mutation processes and are the cause of hereditary diseases (xeroderma pigmentosa, progeria, etc.).

Structure and functions of RNA

The pyrimidine bases of RNA are uracil, cytosine, and the purine bases are adenine and guanine. The RNA nucleotide monosaccharide is represented by ribose.

Allocate three types of RNA: 1) informational(matrix) RNA - mRNA (mRNA), 2) transport RNA - tRNA, 3) ribosomal RNA - rRNA.

The structure and functions of ATP

Go to lectures №3“The structure and function of proteins. Enzymes»

Go to lectures number 5"Cell Theory. Types of cellular organization»

Continuation. See No. 11, 12, 13, 14, 15, 16/2005

Biology lessons in science classes

Advanced Planning, Grade 10

Lesson 19

Equipment: tables on general biology, a diagram of the structure of the ATP molecule, a diagram of the relationship between plastic and energy exchanges.

I. Knowledge Test

Conducting a biological dictation "Organic compounds of living matter"

The teacher reads the theses under the numbers, the students write down in the notebook the numbers of those theses that are suitable in content to their version.

Option 1 - proteins.
Option 2 - carbohydrates.
Option 3 - lipids.
Option 4 - nucleic acids.

1. In its pure form, they consist only of C, H, O atoms.

2. In addition to C, H, O atoms, they contain N and usually S atoms.

3. In addition to the C, H, O atoms, they contain N and P atoms.

4. They have a relatively small molecular weight.

5. The molecular weight can be from thousands to several tens and hundreds of thousands of daltons.

6. The largest organic compounds with a molecular weight of up to several tens and hundreds of millions of daltons.

7. They have different molecular weights - from very small to very high, depending on whether the substance is a monomer or a polymer.

8. Consist of monosaccharides.

9. Consist of amino acids.

10. Consist of nucleotides.

11. They are esters of higher fatty acids.

12. Basic structural unit: "nitrogenous base - pentose - phosphoric acid residue".

13. Basic structural unit: "amino acids".

14. Basic structural unit: "monosaccharide".

15. Basic structural unit: "glycerol-fatty acid".

16. Polymer molecules are built from the same monomers.

17. Polymer molecules are built from similar, but not exactly identical, monomers.

18. Are not polymers.

19. They perform almost exclusively energy, construction and storage functions, in some cases - protective.

20. In addition to energy and construction, they perform catalytic, signal, transport, motor and protective functions;

21. They store and transfer the hereditary properties of the cell and the body.

Option 1 – 2; 5; 9; 13; 17; 20.
Option 2 – 1; 7; 8; 14; 16; 19.
Option 3 – 1; 4; 11; 15; 18; 19.
Option 4– 3; 6; 10; 12; 17; 21.

II. Learning new material

1. The structure of adenosine triphosphoric acid

In addition to proteins, nucleic acids, fats and carbohydrates, a large number of other organic compounds are synthesized in living matter. Among them, an important role in the bioenergetics of the cell is played by adenosine triphosphate (ATP). ATP is found in all plant and animal cells. In cells, adenosine triphosphoric acid is most often present in the form of salts called adenosine triphosphates. The amount of ATP fluctuates and averages 0.04% (on average there are about 1 billion ATP molecules in a cell). The largest amount of ATP is found in skeletal muscles (0.2–0.5%).

The ATP molecule consists of a nitrogenous base - adenine, pentose - ribose and three residues of phosphoric acid, i.e. ATP is a special adenyl nucleotide. Unlike other nucleotides, ATP contains not one, but three phosphoric acid residues. ATP refers to macroergic substances - substances containing a large amount of energy in their bonds.

Spatial model (A) and structural formula (B) of the ATP molecule

From the composition of ATP under the action of ATPase enzymes, a residue of phosphoric acid is cleaved off. ATP has a strong tendency to detach its terminal phosphate group:

ATP 4– + H 2 O ––> ADP 3– + 30.5 kJ + Fn,

because this leads to the disappearance of the energetically unfavorable electrostatic repulsion between neighboring negative charges. The resulting phosphate is stabilized by the formation of energetically favorable hydrogen bonds with water. The charge distribution in the ADP + Fn system becomes more stable than in ATP. As a result of this reaction, 30.5 kJ are released (when a conventional covalent bond is broken, 12 kJ is released).

In order to emphasize the high energy "cost" of the phosphorus-oxygen bond in ATP, it is customary to denote it with the sign ~ and call it a macroenergetic bond. When one molecule of phosphoric acid is cleaved off, ATP is converted to ADP (adenosine diphosphoric acid), and if two molecules of phosphoric acid are cleaved off, then ATP is converted to AMP (adenosine monophosphoric acid). The cleavage of the third phosphate is accompanied by the release of only 13.8 kJ, so that there are only two macroergic bonds in the ATP molecule.

2. Formation of ATP in the cell

The supply of ATP in the cell is small. For example, in a muscle, ATP reserves are enough for 20–30 contractions. But a muscle can work for hours and produce thousands of contractions. Therefore, along with the breakdown of ATP to ADP, reverse synthesis must continuously occur in the cell. There are several ways ATP synthesis in cells. Let's get to know them.

1. anaerobic phosphorylation. Phosphorylation is the process of ATP synthesis from ADP and low molecular weight phosphate (Pn). In this case, we are talking about oxygen-free processes of oxidation of organic substances (for example, glycolysis is the process of oxygen-free oxidation of glucose to pyruvic acid). Approximately 40% of the energy released during these processes (about 200 kJ / mol of glucose) is spent on ATP synthesis, and the rest is dissipated in the form of heat:

C 6 H 12 O 6 + 2ADP + 2Fn -–> 2C 3 H 4 O 3 + 2ATP + 4H.

2. Oxidative phosphorylation- this is the process of ATP synthesis due to the energy of oxidation of organic substances with oxygen. This process was discovered in the early 1930s. 20th century V.A. Engelhardt. Oxygen processes of oxidation of organic substances proceed in mitochondria. Approximately 55% of the energy released in this case (about 2600 kJ / mol of glucose) is converted into the energy of chemical bonds of ATP, and 45% is dissipated in the form of heat.

Oxidative phosphorylation is much more efficient than anaerobic syntheses: if only 2 ATP molecules are synthesized during glycolysis during the breakdown of a glucose molecule, then 36 ATP molecules are formed during oxidative phosphorylation.

3. Photophosphorylation- the process of ATP synthesis due to energy sunlight. This pathway of ATP synthesis is characteristic only for cells capable of photosynthesis (green plants, cyanobacteria). The energy of sunlight quanta is used by photosynthetics in light phase photosynthesis for the synthesis of ATP.

3. Biological significance of ATP

ATP is at the center of metabolic processes in the cell, being the link between the reactions of biological synthesis and decay. The role of ATP in the cell can be compared with the role of a battery, since during the hydrolysis of ATP, the energy necessary for various life processes ("discharge") is released, and in the process of phosphorylation ("charging"), ATP again accumulates energy in itself.

Due to the energy released during ATP hydrolysis, almost all vital processes in the cell and body occur: transmission of nerve impulses, biosynthesis of substances, muscle contractions, transport of substances, etc.

III. Consolidation of knowledge

Solving biological problems

Task 1. When running fast, we often breathe, there is increased sweating. Explain these phenomena.

Task 2. Why do freezing people start stomping and jumping in the cold?

Task 3. In the well-known work by I. Ilf and E. Petrov "The Twelve Chairs" among many useful tips you can also find this: "Breathe deeply, you are excited." Try to justify this advice from the point of view of the energy processes occurring in the body.

IV. Homework

Start preparing for the test and test (dictate test questions - see lesson 21).

Lesson 20

Equipment: tables on general biology.

I. Generalization of the knowledge of the section

Work of students with questions (individually) with subsequent verification and discussion

1. Give examples of organic compounds that include carbon, sulfur, phosphorus, nitrogen, iron, manganese.

2. How can you distinguish by ionic composition living cell from dead?

3. What substances are in the cell in an undissolved form? What organs and tissues do they include?

4. Give examples of macronutrients included in the active centers of enzymes.

5. What hormones contain trace elements?

6. What is the role of halogens in the human body?

7. How are proteins different from artificial polymers?

8. What is the difference between peptides and proteins?

9. What is the name of the protein that is part of hemoglobin? How many subunits does it consist of?

10. What is ribonuclease? How many amino acids are in it? When was it artificially synthesized?

11. Why speed chemical reactions small without enzymes?

12. What substances are transported by proteins through the cell membrane?

13. How do antibodies differ from antigens? Do vaccines contain antibodies?

14. What substances break down proteins in the body? How much energy is released in this case? Where and how is ammonia neutralized?

15. Give an example of peptide hormones: how do they participate in the regulation of cellular metabolism?

16. What is the structure of sugar with which we drink tea? What other three synonyms for this substance do you know?

17. Why is fat in milk not collected on the surface, but is in suspension?

18. What is the mass of DNA in the nucleus of somatic and germ cells?

19. How much ATP is used by a person per day?

20. What proteins do people make clothes from?

Primary structure of pancreatic ribonuclease (124 amino acids)

II. Homework.

Continue preparation for the test and test in the section "Chemical organization of life."

Lesson 21

I. Conducting an oral test on questions

1. Elementary composition of the cell.

2. Characteristics of organogenic elements.

3. The structure of the water molecule. The hydrogen bond and its significance in the "chemistry" of life.

4. Properties and biological functions of water.

5. Hydrophilic and hydrophobic substances.

6. Cations and their biological significance.

7. Anions and their biological significance.

8. Polymers. biological polymers. Differences between periodic and non-periodic polymers.

9. Properties of lipids, their biological functions.

10. Groups of carbohydrates distinguished by structural features.

11. Biological functions of carbohydrates.

12. Elementary composition of proteins. Amino acids. The formation of peptides.

13. Primary, secondary, tertiary and quaternary structures of proteins.

14. Biological function of proteins.

15. Differences between enzymes and non-biological catalysts.

16. The structure of enzymes. Coenzymes.

17. The mechanism of action of enzymes.

18. Nucleic acids. Nucleotides and their structure. The formation of polynucleotides.

19. Rules of E.Chargaff. The principle of complementarity.

20. Formation of a double-stranded DNA molecule and its spiralization.

21. Classes of cellular RNA and their functions.

22. Differences between DNA and RNA.

23. DNA replication. Transcription.

24. Structure and biological role ATP.

25. The formation of ATP in the cell.

II. Homework

Continue preparation for the test in the section "Chemical organization of life."

Lesson 22

I. Conducting a written test

Option 1

1. There are three types of amino acids - A, B, C. How many variants of polypeptide chains consisting of five amino acids can be built. Specify these options. Will these polypeptides have the same properties? Why?

2. All living things mainly consist of carbon compounds, and the analogue of carbon is silicon, the content of which in earth's crust 300 times more than carbon, found in only a very few organisms. Explain this fact in terms of the structure and properties of the atoms of these elements.

3. ATP molecules labeled with radioactive 32P at the last, third phosphoric acid residue were introduced into one cell, and ATP molecules labeled with 32P at the first residue closest to ribose were introduced into another cell. After 5 minutes, the content of inorganic phosphate ion labeled with 32P was measured in both cells. Where will it be significantly higher?

4. Studies have shown that 34% of the total number of nucleotides of this mRNA is guanine, 18% is uracil, 28% is cytosine, and 20% is adenine. Determine the percentage composition of the nitrogenous bases of double-stranded DNA, of which the specified mRNA is a cast.

Option 2

1. Fats are the "first reserve" in energy exchange and are used when the reserve of carbohydrates is depleted. However, in skeletal muscles, in the presence of glucose and fatty acids, the latter are used to a greater extent. Proteins as a source of energy are always used only as a last resort, when the body is starving. Explain these facts.

2. Ions of heavy metals (mercury, lead, etc.) and arsenic are easily bound by sulfide groups of proteins. Knowing the properties of the sulfides of these metals, explain what happens to the protein when combined with these metals. Why are heavy metals poisonous to the body?

3. In the oxidation reaction of substance A into substance B, 60 kJ of energy is released. How many ATP molecules can be maximally synthesized in this reaction? How will the rest of the energy be used?

4. Studies have shown that 27% total number of nucleotides of this mRNA is guanine, 15% is uracil, 18% is cytosine, and 40% is adenine. Determine the percentage composition of the nitrogenous bases of double-stranded DNA, of which the specified mRNA is a mold.

To be continued

Carbohydrates are organic compounds containing carbon, hydrogen and oxygen. Carbohydrates are divided into mono-, di- and polysaccharides.

Monosaccharides - simple sugars, consisting of 3 or more C atoms. Monosaccharides: glucose, ribose and deoxyribose. Not hydrolysable, can crystallize, soluble in water, have a sweet taste

Polysaccharides are formed as a result of the polymerization of monosaccharides. At the same time, they lose the ability to crystallize, sweet taste. An example is starch, glycogen, cellulose.

1. Energy is the main source of energy in the cell (1 gram = 17.6 kJ)

2. structural - are part of the membranes of plant cells (cellulose) and animal cells

3. source for the synthesis of other compounds

4. storage (glycogen - in animal cells, starch - in plant cells)

5. connecting

Lipids- complex compounds of glycerol and fatty acids. Insoluble in water, only in organic solvents. Distinguish between simple and complex lipids.

Lipid functions:

1. structural - the basis for all cell membranes

2. energy (1 g = 37.6 kJ)

3. storage

4. thermal insulation

5. source of intracellular water

ATP - a single universal energy-intensive substance in the cells of plants, animals and microorganisms. With the help of ATP, energy is stored and transported in the cell. ATP is made up of the nitrogenous base adeine, the carbohydrate ribose, and three phosphoric acid residues. Phosphate groups are interconnected with the help of macroergic bonds. The functions of ATP are the transfer of energy.

Squirrels are the predominant substance in all living organisms. Protein is a polymer whose monomer is amino acids (20). Amino acids are connected in a protein molecule using peptide bonds formed between the amino group of one amino acid and the carboxyl group of another. Each cell has a unique set of proteins.

There are several levels of organization of a protein molecule. Primary structure - a sequence of amino acids connected by a peptide bond. This structure determines the specificity of the protein. In secondary the structure of the molecule has the form of a spiral, its stability is provided by hydrogen bonds. Tertiary the structure is formed as a result of the transformation of the helix into a three-dimensional spherical shape - a globule. Quaternary occurs when several protein molecules combine into a single complex. The functional activity of proteins is manifested in the 2,3, or 3rd structure.

The structure of proteins changes under the influence of various chemicals (acids, alkalis, alcohol and others) and physical factors (high and low t, radiation), enzymes. If these changes preserve the primary structure, the process is reversible and is called denaturation. The destruction of the primary structure is called coagulation(irreversible protein breakdown process)

Functions of proteins

1. structural

2. catalytic

3. contractile (proteins actin and myosin in muscle fibers)

4. transport (hemoglobin)

5. regulatory (insulin)

6. signal

7. protective

8. energy (1 g = 17.2 kJ)

Types of nucleic acids. Nucleic acids- phosphorus-containing biopolymers of living organisms that provide storage and transmission of hereditary information. They were discovered in 1869 by the Swiss biochemist F. Miescher in the nuclei of leukocytes, salmon spermatozoa. Subsequently, nucleic acids were found in all plant and animal cells, viruses, bacteria and fungi.

In nature, there are two types of nucleic acids - deoxyribonucleic (DNA) And ribonucleic (RNA). The difference in names is explained by the fact that the DNA molecule contains the five-carbon sugar deoxyribose, and the RNA molecule contains ribose.

DNA is located mainly in the chromosomes of the cell nucleus (99% of the total cell DNA), as well as in mitochondria and chloroplasts. RNA is part of ribosomes; RNA molecules are also found in the cytoplasm, matrix of plastids and mitochondria.

Nucleotides- structural components of nucleic acids. Nucleic acids are biopolymers whose monomers are nucleotides.

Nucleotides- complex substances. Each nucleotide consists of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose) and a phosphoric acid residue.

There are five main nitrogenous bases: adenine, guanine, uracil, thymine, and cytosine.

DNA. The DNA molecule consists of two polynucleotide chains helically twisted relative to each other.

The composition of the nucleotides of the DNA molecule includes four types of nitrogenous bases: adenine, guanine, thymine and cytocin. In a polynucleotide chain, adjacent nucleotides are linked by covalent bonds.

The polynucleotide chain of DNA is twisted in the form of a spiral like a spiral staircase and connected to another, complementary chain to it using hydrogen bonds formed between adenine and thymine (two bonds), as well as guanine and cytosine (three bonds). Nucleotides A and T, G and C are called complementary.

As a result, in any organism, the number of adenyl nucleotides is equal to the number of thymidyl, and the number of guanyl nucleotides is equal to the number of cytidyl. Due to this property, the sequence of nucleotides in one chain determines their sequence in another. This ability to selectively combine nucleotides is called complementarity, and this property underlies the formation of new DNA molecules based on the original molecule (replications, i.e. doubling).

When conditions change, DNA, like proteins, can undergo denaturation, which is called melting. With a gradual return to normal conditions, DNA renatures.

Function of DNA is the storage, transmission and reproduction in a number of generations of genetic information. The DNA of any cell encodes information about all the proteins of a given organism, about which proteins, in what sequence and in what quantity will be synthesized. The sequence of amino acids in proteins is recorded in DNA by the so-called genetic (triplet) code.

Main property DNA is its ability to replicate.

Replication - This is the process of self-duplication of DNA molecules, which occurs under the control of enzymes. Replication occurs before each nuclear division. It begins with the fact that the DNA helix is temporarily unwound under the action of the DNA polymerase enzyme. On each of the chains formed after the breaking of hydrogen bonds, a daughter strand of DNA is synthesized according to the principle of complementarity. The material for synthesis is the free nucleotides that are in the nucleus.

Thus, each polynucleotide chain plays the role matrices for a new complementary strand (therefore, the process of doubling DNA molecules refers to the reactions matrix synthesis). The result is two DNA molecules, each of which "one chain remains from the parent molecule (half), and the other is newly synthesized. Moreover, one new chain is synthesized continuous, and the second - first in the form of short fragments, which are then sewn into a long chain a special enzyme - DNA ligase.As a result of replication, two new DNA molecules are an exact copy of the original molecule.

The biological meaning of replication lies in the exact transfer of hereditary information from the mother cell to the daughter cells, which occurs during the division of somatic cells.

RNA. The structure of RNA molecules is in many ways similar to the structure of DNA molecules. However, there are also a number of significant differences. In the RNA molecule, instead of deoxyribose, the composition of nucleotides includes ribose, and instead of the thymidyl nucleotide (T) - uridyl (U). The main difference from DNA is that the RNA molecule is a single strand. However, its nucleotides are capable of forming hydrogen bonds with each other (for example, in tRNA, rRNA molecules), but in this case we are talking about an intrastrand connection of complementary nucleotides. RNA chains are much shorter than DNA.

There are several types of RNA in the cell, which differ in the size of the molecules, structure, location in the cell and functions:

1. Information (matrix) RNA (mRNA) - transfers genetic information from DNA to ribosomes

2. Ribosomal RNA (rRNA) - is part of ribosomes

3. 3. Transfer RNA (tRNA) - transfers amino acids to ribosomes during protein synthesis

From the course of biology of plants and animals, remember where hereditary information is stored in cells. What substances are responsible for the storage and reproduction of hereditary information? Are these substances the same in plants and animals?

Nucleic acids and nucleotides

Nucleic acid molecules are large organic molecules - biopolymers, the monomers of which are nucleotides. Each nucleotide consists of three components - a nitrogenous base, a monosaccharide (ribose or deoxyribose) and an orthophosphate acid residue (Fig. 8.1).

The composition of nucleic acids includes five types of nitrogenous bases (Fig. 8.2). There are, in fact, five types of nucleotides: thymidyl (base - thymine), cytidyl (base - cytosine), uridyl (base - uracil), adenyl (base - adenine), guanyl (base - guanine).

In the cells of living organisms, individual nucleotides are also used in various metabolic processes as independent compounds.

When nucleic acid molecules are formed between the orthophosphate acid residue of one nucleotide and the monosaccharide of another

a strong covalent bond is formed. Therefore, the nucleic acids formed in this way have the form of a chain in which the nucleotides are sequentially arranged one after the other. Their number in one biopolymer molecule can reach several million.

DNA and RNA

There are two types of nucleic acids in the cells of living organisms - RNA (ribonucleic acid) and DNA (deoxyribonucleic acid). They differ from each other in composition and structural features.

The main function of DNA and RNA is the storage and reproduction of hereditary information, which is facilitated by the structure of their molecules.

RNA stores hereditary information less securely than DNA, so this way storage uses only part of the viruses.

The structure of nucleic acid molecules

DNA nucleotides are composed of the monosaccharide deoxyribose and four nitrogenous bases - adenine, thymine, cytosine and guanine. And the DNA molecules themselves usually consist of two nucleotide chains, which are interconnected by hydrogen bonds (Fig. 8.3).

RNA nucleotides contain the monosaccharide ribose instead of deoxyribose, and uracil instead of thymine. An RNA molecule usually consists of a single nucleotide chain, the various fragments of which form hydrogen bonds with each other. Three such bonds are formed between guanine and cytosine, and two between adenine and thymine or adenine and uracil.

The DNA molecule consists of two nucleotide chains connected according to the principle of complementarity (addition): in front of each nucleotide of one chain, the nucleotide of the second chain that corresponds to it is placed. So, opposite the adenyl nucleotide is thymidyl, and opposite the cytidyl - guanyl (Fig. 8.4). Therefore, in DNA molecules, the number of adenyl nucleotides is always equal to the number of thymidyl nucleotides, and the number of guanyl nucleotides is always equal to the number of cytidyl nucleotides.

ATP and its role in the life of cells

Not only RNA and DNA, but also individual nucleotides take an active part in the life of the cell. Particularly important are the compounds of nucleotides with orthophosphate acid residues. From one to three such residues can be attached to a nucleotide. Accordingly, they are called according to the number of these residues: ATP - adenosine triorthophosphate (adenosine triorthophosphoric acid), GTP - guanosine triorthophosphate, ADP - adenosine diorthophosphate, AMP - adenosine monoorthophosphate. all nucleotides that make up nucleic acids are monophosphates. Tri- and diphosphates also play an important role in the biochemical processes of cells.

The most abundant in the cells of living organisms is ATP. It plays the role of a universal source of energy for biochemical reactions, and also participates in the processes of growth, movement and reproduction of cells. A large number of ATP molecules are formed in the processes of cellular respiration and photosynthesis.

Energy Conversion and Fusion Reactions in Biological Systems

ATP provides energy for most of the processes that occur in cells. First of all, these are the processes of synthesis of organic substances, which are carried out with the help of enzymes.

In order for enzymes to carry out a biochemical reaction, in most cases they require energy.

ATP molecules, when interacting with enzymes, break down into two molecules - orthophosphate acid and ADP. This releases energy:

This energy is used by enzymes to work. Why ATP? Because the bond of orthophosphate acid residues in this molecule is not ordinary, but macroergic (high-energy) (Fig. 8.5). A lot of energy is required to form this bond, but even during its destruction, energy is released in large quantities.

When molecules of carbohydrates, proteins, lipids in cells are broken down, energy is released. The cell stores this energy. To do this, one or two residues of orthophosphate acid are attached to nucleotides of monoorthophosphates (for example, AMP) and molecules of di- or triorthophosphates (respectively, ADP or ATP) are formed. The resulting bonds are macroergic. Thus,

ADP contains one macroergic bond, and ATP has two. during the synthesis of new organic compounds, macroergic bonds are destroyed and provide the corresponding processes with energy.

All cellular life forms on our planet contain both RNA and DNA in their cells. But in viruses there is only one type of nucleic acid. their virions contain either RNA or DNA under the protein coat. Only when a virus enters a host cell does it usually begin to synthesize both DNA and RNA.

Nucleic acids are biopolymers that are present in living organisms in the form of DNA and RNA. Their monomers are nucleotides. DNA usually has the form of a double helix, consisting of two strands. RNA is most often in the form of a single strand. The main function of nucleic acids is the storage and reproduction of genetic information. Nucleotides are also involved in the biochemical processes of the cell, and ATP plays the role of a universal energy source for biochemical reactions.

Test your knowledge

1. How is DNA different from RNA? 2. Why do living organisms need nucleic acids? 3. What functions does ATP perform in cells? 4. Complete the second strand of DNA according to the principle of complementarity, if the first strand is: AGGTTATATCGCCTAGAATCGGGAA. 5*. DNA is not capable of being a catalyst for biochemical reactions. But some RNA molecules (they are called ribozymes) can be catalysts. What features of the structure of these molecules can be associated with this? 6*. Why are macroergic bonds convenient for use in the biochemical processes of a cell?

Generalizing tasks to the topic " Chemical composition cells and biological molecules

In tasks 1-9, choose one correct answer.

1 Depicted in fig. 1 structure performs the function:

a) stores and reproduces hereditary information

b) transports substances

B) creates a supply of nutrients

d) catalyzes reactions

2) From the same monomers as the substance in Fig. 1, consists of:

a) collagen b) starch c) RNA d) estrogen

3) the substance in fig. 1 can accumulate:

a) on the outer membrane of mitochondria

b) in the yeast cell wall

B) in human liver cells

d) in corn chloroplasts

4 Depicted in fig. 2 structure is a component:

a) plant cell wall

b) proteins

d) the inner layer of the cell membrane

5) Number 3 in fig. 2 marked:

a) a carbonyl group c) a carboxyl group

b) hydroxyl group d) radical

6) Amino group in fig. 2 is marked with a number:

a) 1 b) 2 c) 3 d) 4

7) Structure in fig. 2 is a monomer:

a) nucleic acid c) lipid

b) protein d) polysaccharide

8) Monosaccharide in fig. 3 is marked with a number:

a) 1 b) 2 c) 3 d) 4

9) The structure in fig. 3 is a monomer:

a) nucleic acid c) protein

b) lipid d) polysaccharide

10 Write the names of the groups of organic substances to which the molecules shown in the figures belong:

11 Consider structural formula the molecule shown in the figure. Explain how the structure of this molecule allows it to perform its functions effectively.

12 Complete the complementary DNA strand: ATTGACCCGATTAGCC.

13 Establish a correspondence between the groups of organic substances and the substances that belong to them.

Substance groups

1 proteins a) progesterone

2 carbohydrates b) hemoglobin

3 lipids c) starch

d) insulin

e) fructose

e) testosterone

Test your knowledge on the topic "The chemical composition of the cell and biological molecules."

Mini-guide

Information about organic substances

Structure organic molecule on the example of alanine

Types of bonds in a protein molecule

covalent bonds

They are formed between the atoms of elements in a molecule of a substance due to common electron pairs. Protein molecules have peptide and disulfide bonds. Provide strong chemical interaction.

Peptide bond

Peptide bonds occur between the carboxyl group (-COOH) of one amino acid and the amino group (-NH 2) of another amino acid.

disulfide bond

A disulfide bond can occur between different regions of the same polypeptide chain, while it keeps this chain in a bent state. If a disulfide bond is formed between two polypeptides, then it combines them into one molecule.

Non-covalent bonds

Protein molecules have hydrogen, ionic bonds and hydrophobic interactions. Provide weak chemical interactions.

hydrogen bond

It is formed between the positively charged H atoms of one functional group and the negatively charged O or N atom, which has an unshared electron pair, of another functional group.

Ionic bond

It is formed between positively and negatively charged functional groups (additional carboxyl and amino groups) that are found in the radicals of lysine, arginine, histidine, aspartic and glutamic acids.

hydrophobic

Interaction

It is formed between radicals of hydrophobic amino acids.

This is textbook material.