Cards

ATP is characterized by the fact that it has a polymeric structure. The structure and functions of nucleic acids atf. The concept of a nucleotide and its properties

Recall what a monomer and a polymer are. What substances are protein monomers? How are proteins as polymers different from starch?

Nucleic acids occupy a special place among organic matter cells. They were first isolated from the nuclei of cells, for which they got their name (from the Latin. Nucleus - the nucleus). Subsequently, nucleic acids were found in the cytoplasm and in some other cell organelles. But their original name has been preserved.

Nucleic acids, like proteins, are polymers, but their monomers, nucleotides, have a more complex structure. The number of nucleotides in a chain can reach 30,000. Nucleic acids are the most high-molecular organic substances of a cell.

Rice. 24. Structure and types of nucleotides

There are two types of nucleic acids found in cells: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They differ in nucleotide composition, structure of the polynucleotide chain, molecular weight and functions performed.

Rice. 25. Polynucleotide chain

Composition and structure of DNA. The composition of the nucleotides of the DNA molecule includes phosphoric acid, deoxyribose carbohydrate (which is the reason for the name DNA) and nitrogenous bases - adenine (A), thymine (T), guanine (G), cytosine (C) (Fig. 24, 25).

These bases correspond in pairs to each other in structure (A = T, G = C) and can easily be combined using hydrogen bonds. Such paired bases are called complementary (from Latin complementum - addition).

English scientists James Watson and Francis Crick in 1953 established that the DNA molecule consists of two spirally twisted chains. The backbone of the chain is formed by the residues of phosphoric acid and deoxyribose, and the nitrogenous bases are directed inside the helix (Fig. 26, 27). Two chains are connected to each other by hydrogen bonds between complementary bases.

Rice. 26. Diagram of a DNA molecule

In cells, DNA molecules are located in the nucleus. They form strands of chromatin, and before cell division, they spiralize, combine with proteins and turn into chromosomes. In addition, specific DNA is found in mitochondria and chloroplasts.

DNA in a cell is responsible for the storage and transmission of hereditary information. It encodes information about the structure of all proteins in the body. The number of DNA molecules serves as a genetic trait of a particular type of organism, and the nucleotide sequence is specific for each individual.

Structure and types of RNA. The composition of the RNA molecule includes phosphoric acid, carbohydrate - ribose (hence the name ribonucleic acid), nitrogenous bases: adenine (A), uracil (U), guanine (G), cytosine (C). Instead of thymine, uracil is found here, which is complementary to adenine (A = Y). RNA molecules, unlike DNA, consist of a single polynucleotide chain (Fig. 25), which can have straight and helical sections, form loops between complementary bases using hydrogen bonds. The molecular weight of RNA is much lower than that of DNA.

In cells, RNA molecules are found in the nucleus, cytoplasm, chloroplasts, mitochondria, and ribosomes. There are three types of RNA, which have different molecular weights, molecular shapes, and perform different functions.

Messenger RNAs (mRNAs) carry information about the structure of a protein from DNA to the site of its synthesis on ribosomes. Each mRNA molecule contains the complete information necessary for the synthesis of one protein molecule. Of all types of RNA, the largest mRNAs.

Rice. 27. Double helix of the DNA molecule (3D model)

Transfer RNAs (tRNAs) are the shortest molecules. Their structure resembles a clover leaf in shape (Fig. 62). They transport amino acids to the site of protein synthesis on ribosomes.

Ribosomal RNA (rRNA) make up more than 80% of the total mass of RNA in the cell and, together with proteins, are part of the ribosome.

ATP. In addition to polynucleotide chains, the cell contains mononucleotides that have the same composition and structure as the nucleotides that make up DNA and RNA. The most important of these is ATP - adenosine triphosphate.

The ATP molecule consists of ribose, adenine, and three phosphoric acid residues, between which there are two high-energy bonds (Fig. 28). The energy of each of them is 30.6 kJ/mol. Therefore, it is called macroergic, in contrast to a simple bond, the energy of which is about 13 kJ / mol. When one or two phosphoric acid residues are cleaved from an ATP molecule, an ADP (adenosine diphosphate) or AMP (adenosine monophosphate) molecule is formed, respectively. In this case, energy is released two and a half times more than during the splitting of other organic substances.

Rice. 28. The structure of the alenosine triphosphate (ATP) molecule and its role in energy conversion

ATP is a key substance of metabolic processes in the cell and a universal source of energy. Synthesis of ATP molecules occurs in mitochondria, chloroplasts. Energy is stored as a result of oxidation reactions of organic substances and accumulation of solar energy. The cell uses this stored energy in all life processes.

Lesson learned exercises

What is a nucleic acid monomer? What components does it consist of?
How are nucleic acids, as polymers, different from proteins?
What is complementarity? Name the tribal foundations. What connections are formed between them?
What role do RNA molecules play in the living bodies of nature?
The function of ATP in a cell is sometimes compared to a battery or battery. Explain the meaning of this comparison.

All life on the planet consists of many cells that maintain the orderliness of their organization due to the genetic information contained in the nucleus. It is stored, implemented and transmitted by complex high-molecular compounds - nucleic acids, consisting of monomer units - nucleotides. The role of nucleic acids cannot be overestimated. The stability of their structure determines the normal vital activity of the organism, and any deviations in the structure inevitably lead to a change in the cellular organization, the activity of physiological processes and the viability of cells as a whole.

The concept of a nucleotide and its properties

Each or RNA is assembled from smaller monomeric compounds - nucleotides. In other words, a nucleotide is a building material for nucleic acids, coenzymes and many other biological compounds that are essential for a cell in the course of its life.

The main properties of these irreplaceable substances include:

Storage of information about and inherited traits;
. exercising control over growth and reproduction;
. participation in metabolism and many other physiological processes occurring in the cell.

Speaking of nucleotides, one cannot but dwell on such an important issue as their structure and composition.

Each nucleotide is made up of:

sugar residue;
. nitrogenous base;
. a phosphate group or a phosphoric acid residue.

We can say that a nucleotide is a complex organic compound. Depending on the species composition of nitrogenous bases and the type of pentose in the nucleotide structure, nucleic acids are divided into:

Deoxyribonucleic acid, or DNA;
. ribonucleic acid, or RNA.

Composition of nucleic acids

In nucleic acids, sugar is represented by pentose. This is a five-carbon sugar, in DNA it is called deoxyribose, in RNA it is called ribose. Each pentose molecule has five carbon atoms, four of which, together with an oxygen atom, form a five-membered ring, and the fifth is included in the HO-CH2 group.

The position of each carbon atom in a pentose molecule is indicated by an Arabic numeral with a prime (1C´, 2C´, 3C´, 4C´, 5C´). Since all reading processes from a nucleic acid molecule have a strict direction, the numbering of carbon atoms and their arrangement in the ring serve as a kind of indicator of the correct direction.

On the hydroxyl group, a phosphoric acid residue is attached to the third and fifth carbon atoms (3С´ and 5С´). It determines the chemical affiliation of DNA and RNA to a group of acids.

A nitrogenous base is attached to the first carbon atom (1C´) in the sugar molecule.

Species composition of nitrogenous bases

DNA nucleotides according to the nitrogenous base are represented by four types:

Adenine (A);
. guanine (G);
. cytosine (C);
. thymine (T).

The first two belong to the class of purines, the last two are pyrimidines. In terms of molecular weight, purines are always heavier than pyrimidines.

RNA nucleotides by nitrogenous base are represented by:

Adenine (A);
. guanine (G);
. cytosine (C);
. uracil (U).

Uracil, like thymine, is a pyrimidine base.

In the scientific literature, one can often find another designation of nitrogenous bases - in Latin letters (A, T, C, G, U).

Let us dwell in more detail on the chemical structure of purines and pyrimidines.

Pyrimidines, namely cytosine, thymine and uracil, in their composition are represented by two nitrogen atoms and four carbon atoms, forming a six-membered ring. Each atom has its own number from 1 to 6.

Purines (adenine and guanine) are composed of pyrimidine and imidazole or two heterocycles. The purine base molecule is represented by four nitrogen atoms and five carbon atoms. Each atom is numbered from 1 to 9.

As a result of the combination of a nitrogenous base and a pentose residue, a nucleoside is formed. A nucleotide is a compound of a nucleoside and a phosphate group.

Formation of phosphodiester bonds

It is important to understand the question of how nucleotides are connected into a polypeptide chain and form a nucleic acid molecule. This happens due to the so-called phosphodiester bonds.

The interaction of two nucleotides gives a dinucleotide. The formation of a new compound occurs by condensation, when a phosphodiester bond occurs between the phosphate residue of one monomer and the hydroxy group of the pentose of another.

The synthesis of a polynucleotide is the repeated repetition of this reaction (several million times). The polynucleotide chain is built through the formation of phosphodiester bonds between the third and fifth carbons of sugars (3C' and 5C').

Polynucleotide assembly is a complex process that occurs with the participation of the enzyme DNA polymerase, which ensures the growth of the chain from only one end (3´) with a free hydroxyl group.

DNA molecule structure

A DNA molecule, like a protein, can have a primary, secondary, or tertiary structure.

The sequence of nucleotides in the DNA chain determines its primary formation due to hydrogen bonds, which are based on the principle of complementarity. In other words, during the synthesis of a double, a certain pattern operates: adenine of one chain corresponds to the thymine of the other, guanine to cytosine, and vice versa. Pairs of adenine and thymine or guanine and cytosine are formed due to two in the first and three in the last case hydrogen bonds. Such a connection of nucleotides provides a strong bond between the chains and an equal distance between them.

Knowing the nucleotide sequence of one strand of DNA, by the principle of complementarity or addition, you can complete the second one.

The tertiary structure of DNA is formed by complex three-dimensional bonds, which makes its molecule more compact and able to fit in a small cell volume. So, for example, the length of E. coli DNA is more than 1 mm, while the length of the cell is less than 5 microns.

The number of nucleotides in DNA, namely their quantitative ratio, obeys the Chergaff rule (the number of purine bases is always equal to the number of pyrimidine bases). The distance between nucleotides is a constant value equal to 0.34 nm, as is their molecular weight.

Structure of the RNA molecule

RNA is represented by a single polynucleotide chain formed through between the pentose (in this case, ribose) and the phosphate residue. It is much shorter than DNA in length. By species composition nitrogenous bases in the nucleotide also have differences. In RNA, uracil is used instead of the pyrimidine base of thymine. Depending on the functions performed in the body, RNA can be of three types.

Ribosomal (rRNA) - usually contains from 3000 to 5000 nucleotides. As a necessary structural component, it takes part in the formation of the active center of ribosomes, the site of one of the most important processes in the cell - protein biosynthesis.
. Transport (tRNA) - consists of an average of 75 - 95 nucleotides, carries out the transfer of the desired amino acid to the site of polypeptide synthesis in the ribosome. Each type of tRNA (at least 40) has its own unique sequence of monomers or nucleotides.
. Information (mRNA) - the nucleotide composition is very diverse. Transfers genetic information from DNA to ribosomes, acts as a matrix for the synthesis of a protein molecule.

The role of nucleotides in the body

Nucleotides in the cell perform a number of important functions:

They are used as structural blocks for nucleic acids (nucleotides of the purine and pyrimidine series);
. participate in many metabolic processes in the cell;
. are part of ATP - the main source of energy in cells;
. act as carriers of reducing equivalents in cells (NAD+, NADP+, FAD, FMN);
. perform the function of bioregulators;
. can be considered as the second messengers of extracellular regular synthesis (for example, cAMP or cGMP).

A nucleotide is a monomeric unit that forms more complex compounds - nucleic acids, without which the transfer of genetic information, its storage and reproduction is impossible. Free nucleotides are the main components involved in signaling and energy processes that support the normal functioning of cells and the body as a whole.

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 great amount tissue and organ samples 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 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 "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 strand of DNA, 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 the 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 steps 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 most studied: 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 cause hereditary diseases (xeroderma pigmentosa, 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.

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.

Function of DNA- storage and transmission of hereditary information.

Replication (reduplication) of DNA

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 most studied: 1) photoreparation, 2) excise or pre-replicative repair, 3) post-replicative repair.

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. Main 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 pathways for the synthesis of ATP 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 during this (about 2600 kJ / mol of glucose) is converted into energy chemical bonds ATP, and 45% is dissipated as 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 the energy of 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 the light phase of 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: 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 a living cell be distinguished from a dead one by ionic composition?

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 is the rate of chemical reactions without enzymes low?

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 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 silicon, the analogue of carbon, the content of which in the earth's crust is 300 times more than carbon, is found only in 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 mold.

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% of the 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