The human body contains a large number of organic compounds, without which it is impossible to imagine a stable course of metabolic processes that support the vital functions of everyone. One of these substances are nucleotides - these are phosphorus esters of nucleosides, which play a critical role in the transmission of information data, as well as chemical reactions with the release of intracellular energy.

As independent organic units, they form the filling composition of all nucleic acids and most coenzymes. Let's take a closer look at what nucleoside phosphates are and what role they play in the human body.

What does the substance nucleotide consist of? It is considered an extremely ester, belonging to the group of phosphorus acids and nucleosides, which in their biochemical properties are classified as N-glycosides and contain heterocyclic fragments associated with glucose molecules and a nitrogen atom.

In nature, the most common nucleotides are DNA.

In addition, organic substances with similar structural characteristics are also distinguished: ribonucleotides, as well as deoxyribonucleotides. All of them, without exception, are monomeric molecules belonging to biological substances of the polymer type that are complex in structure.

From them, RNA and DNA of all living beings are formed, ranging from the simplest microorganisms and viral infections to the human body.

The remainder of the molecular structure of phosphorus among the nucleoside phosphates forms an ester bond with two, three, and in some cases with five hydroxyl groups at once. Almost all nucleotides, without exception, are essential substances that are formed from orthophosphoric acid residues, therefore their bonds are stable and do not disintegrate under the influence of unfavorable factors of the internal and external environment.

Note! The structure of nucleotides is always complex and is based on monoesters. The nucleotide sequence can change under the influence of stress factors.

Biological role

The influence of nucleotides on the course of all processes in the body of living beings is studied by scientists who study the molecular structure of the intracellular space.

Based on laboratory findings obtained based on the results of many years of work by scientists from around the world, the following role of nucleoside phosphates is distinguished:

• a universal source of vital energy, due to which cells are nourished and, accordingly, the normal functioning of tissues that form internal organs, biological fluids, epithelial cover, and the vascular system is maintained;
• are transporters of glucose monomers in cells of any type (this is one of the forms of carbohydrate metabolism, when consumed sugar, under the influence of digestive enzymes, is transformed into glucose, which is carried to every corner of the body along with nucleoside phosphates);
• perform the function of a coenzyme (vitamin and mineral compounds that help provide cells with nutrients);
• complex and cyclic mononucleotides are biological conductors of hormones that spread along with the blood flow, and also enhance the effect of neural impulses;
• allosterically regulate the activity of digestive enzymes produced by pancreatic tissues.

Nucleotides are part of nucleic acids. They are connected by three and five phosphodiester bonds. Geneticists and scientists who have devoted their lives to molecular biology continue laboratory research on nucleoside phosphates, so every year the world learns even more interesting things about the properties of nucleotides.

The nucleotide sequence is a type of genetic equilibrium and balance of the arrangement of amino acids in the DNA structure, a peculiar order of placement of ester residues in the composition of nucleic acids.

It is determined using the traditional method of sequencing biological material selected for analysis.

T – thymine;

A – adenine;

G – guanine;

C – cytosine;

R – GA adenine in complex with guanine and purine bases;

Y – TC pyrimidine compounds;

K – GT nucleotides containing a keto group;

M – AC included in the amino group;

S – GC powerful, distinguished by three hydrogen compounds;

W – AT are unstable, forming only two hydrogen bonds.

The sequence of nucleotides may change, and designations in Latin letters are necessary in cases where the order of arrangement of ether compounds is unknown, is unimportant, or the results of primary research already exist.

The largest number of variants and combinations of nucleoside phosphates is characteristic of DNA. To write RNA ether compounds, the symbols A, C, G, U are sufficient. The last letter designation is the substance uridine, which is found only in RNA. A sequence of symbolic notations is always written without spaces.

Useful video: nucleic acids (DNA and RNA)

How many nucleotides are in DNA

In order to understand in as much detail as possible what we are talking about, you should have a clear understanding of DNA itself. This is a separate type of molecules that have an elongated shape and consist of structural elements, namely nucleoside phosphates. How many nucleotides are there in DNA? There are 4 types of ether compounds of this type that are part of DNA. These are adenine, thymine, cytosine and guanine. They all form a single chain, from which the molecular structure of DNA is formed.

The structure of DNA was first deciphered back in 1953 by American scientists Francis Crick and James Watson. One molecule of deoxyribonucleic acid contains two chains of nucleoside phosphates. They are placed in such a way that they look like a spiral twisting around its axis.

Note! The number of nucleotides in DNA is constant and limited to only four types - this discovery has brought humanity closer to deciphering the complete human genetic code.

In this case, the structure of the molecule has one important feature. All nucleotide chains have the property of complementarity. This means that only etheric compounds of a certain type are placed opposite each other. It is known that adenine is always located opposite thymine. No other substance except guanine can be found opposite cytosine. Such nucleotide pairs form the principle of complementarity and are inseparable.

Weight and length

With the help of complex mathematical calculations and laboratory studies, scientists were able to establish the exact physical and biological properties of the ether compounds that form the molecular structure of deoxyribonucleic acid.

It is known that the extended length of one intracellular residue consisting of amino acids in a single polypeptide chain is 3.5 angstroms. The average mass of one molecular residue is 110 amu.

In addition, monomers of the nucleotide type are also isolated, which are formed not only from amino acids, but also have ether components. These are monomers of DNA and RNA. Their linear length is measured directly inside the nucleic acid and is at least 3.4 angstroms. The molecular weight of one nucleoside phosphate is within 345 amu. These are the initial data that are used in practical laboratory work dedicated to experiments, genetic research and other scientific activities.

Medical designations

Genetics, as a science, developed in a period when there was no research into the structure of the DNA of humans and other living beings at the molecular level. Therefore, during the period of pre-molecular genetics, nucleotide bonds were designated as the smallest element in the structure of the DNA molecule. Both previously and currently, essential substances of this type have been subject to. It could be spontaneous or induced, which is why the term “recon” is also used to designate nucleoside phosphates with a damaged structure.

To define the concept of the occurrence of a possible mutation in nitrogenous compounds of nucleotide bonds, the term “mouton” is used. These designations are more in demand in laboratory work with biological material. They are also used by genetic scientists who study the structure of DNA molecules, the ways of transmitting hereditary information, methods of encoding it, and possible combinations of genes obtained as a result of the fusion of the genetic potential of two sexual partners.

Useful video: nucleotide structure

Conclusion

Based on the above, we can conclude that nucleoside phosphates are an important component of the intracellular structure in the human body and any living creature. Due to essential substances of this type, most of not only genetic information is transmitted from parents to offspring, but also metabolic processes are carried out in the tissues of all vital organs.

Like proteins, nucleic acids are biopolymers, and their function is to store, implement and transmit genetic (hereditary) information in living organisms.

There are two types of nucleic acids - deoxyribonucleic acids (DNA) and ribonucleic acids (RNA). The monomers in nucleic acids are nucleotides. Each of them contains a nitrogenous base, a five-carbon sugar (deoxyribose in DNA, ribose in RNA) and a phosphoric acid residue.

DNA contains four types of nucleotides, differing in the nitrogenous base in their composition - adenine (A), guanine (G), cytosine (C) and thymine (T). The RNA molecule also contains 4 types of nucleotides with one of the nitrogenous bases - adenine, guanine, cytosine and uracil (U). Thus, DNA and RNA differ both in the sugar content of the nucleotides and in one of the nitrogenous bases (Table 1).

Table 1

Components of DNA and RNA nucleotides

DNA and RNA molecules differ significantly in their structure and functions.

A DNA molecule can include a huge number of nucleotides - from several thousand to hundreds of millions (truly giant DNA molecules can be “seen” using an electron microscope). Structurally, it is a double helix of polynucleotide chains(Fig. 1), connected by hydrogen bonds between the nitrogenous bases of nucleotides. Thanks to this, the polynucleotide chains are firmly held next to each other.

When studying different DNA (in different types of organisms), it was found that adenine of one chain can only bind to thymine, and guanine can only bind to cytosine of the other. Consequently, the order of arrangement of nucleotides in one chain strictly corresponds to the order of their arrangement in the other. This phenomenon is called complementarity(i.e. complements), and the opposite polynucleotide chains are called complementary. This is what determines the unique property of DNA among all inorganic and organic substances - self-reproduction ability or doubling(Fig. 2). In this case, first the complementary chains of DNA molecules diverge (under the influence of a special enzyme, the bonds between the complementary nucleotides of the two chains are destroyed). Then, on each chain, the synthesis of a new (“missing”) complementary chain begins at the expense of free nucleotides, which are always available in large quantities in the cell. As a result, instead of one (“mother”) DNA molecule, two (“daughter”) new ones are formed, identical in structure and composition to each other, as well as to the original DNA molecule. This process always precedes cell division and ensures the transmission of hereditary information from the mother cell to the daughter and all subsequent generations.

Rice. 1. DNA double helix. Two chains are twisted around one another. Each chain (shown as a ribbon) consists of alternating sugar units and phosphate groups. Hydrogen bonds between nitrogenous bases (A, T, G and C) hold the two chains together

Rice. 2.DNA replication. The double helix “unfastens” according toweak hydrogen bonds connecting complementary the bases of two chains. Each of the old circuits serves as a matrixto form a new one: nucleotides with complementary the bases line up against the old chain and connecttogether

RNA molecules are usually single-stranded (unlike DNA) and contain a significantly smaller number of nucleotides. There are three types of RNA (Table 2), differing in the size of the molecules and the functions they perform - informational (mRNA), ribosomal (rRNA) and transport (tRNA).

table 2

ThreekindRNA

Messenger RNA (i-RNA) is located in the nucleus and cytoplasm of the cell, has the longest polynucleotide chain among RNAs and performs the function of transferring hereditary information from the nucleus to the cytoplasm of the cell.

Transfer RNA (tRNA) is also found in the nucleus and cytoplasm of the cell; its chain has the most complex structure and is also the shortest (75 nucleotides). T-RNA delivers amino acids to ribosomes during the process of translation - protein biosynthesis.

Ribosomal RNA (rRNA) is found in the nucleolus and ribosomes of the cell and has a medium-length chain. All types of RNA are formed during the transcription of the corresponding DNA genes.

Nucleic acids. ATP

Nucleic acids(from Latin nucleus - core) - acids first discovered in the study of leukocyte nuclei; were opened in 1868 by I.F. Miescher, Swiss biochemist. Biological significance nucleic acids - storage and transmission of hereditary information; they are necessary for the maintenance of life and for its reproduction.

Nucleic acids

DNA nucleotide and RNA nucleotide have similarities and differences.

DNA nucleotide structure

Structure of RNA nucleotide

The DNA molecule is a double strand twisted in a spiral.

An RNA molecule is a single strand of nucleotides, similar in structure to a single strand of DNA. Only instead of deoxyribose, RNA includes another carbohydrate - ribose (hence the name), and instead of thymine - uracil.

The two strands of DNA are connected to each other by hydrogen bonds. In this case, an important pattern is observed: opposite the nitrogenous base adenine A in one chain is the nitrogenous base thymine T in the other chain, and opposite guanine G is always cytosine C. These base pairs are called complementary pairs.

Thus, principle of complementarity(from the Latin complementum - addition) is that each nitrogenous base included in the nucleotide corresponds to another nitrogenous base. Strictly defined base pairs arise (A - T, G - C), these pairs are specific. There are three hydrogen bonds between guanine and cytosine, and two hydrogen bonds arise between adenine and thymine in the DNA nucleotide, and in RNA, two hydrogen bonds arise between adenine and uracil.

Hydrogen bonds between nitrogenous bases of nucleotides

G ≡ C G ≡ C

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

Thus, the quantitative content of nitrogenous bases in DNA is subject to certain rules:

1) The sum of adenine and guanine is equal to the sum of cytosine and thymine A + G = C + T.

2) The sum of adenine and cytosine is equal to the sum of guanine and thymine A + C = G + T.

3) The amount of adenine is equal to the amount of thymine, the amount of guanine is equal to the amount of cytosine A = T; G = C.

When conditions change, DNA, like proteins, can undergo denaturation, which is called melting.

DNA has unique properties: the ability to self-replicate (replication, reduplication) and the ability to self-heal (repair). Replication ensures accurate reproduction in daughter molecules of the information that was recorded in the mother molecule. But sometimes errors occur during the replication process. The ability of a DNA molecule to correct errors that occur in its chains, that is, to restore the correct sequence of nucleotides, is called reparation.

DNA molecules are found mainly in the nuclei of cells and in small quantities in mitochondria and plastids - chloroplasts. DNA molecules are carriers of hereditary information.

Structure, functions and localization in the cell. There are three types of RNA. The names are related to the functions performed:

Comparative characteristics of nucleic acids

Adenosine phosphoric acids - a denosine triphosphoric acid (ATP), A denosine diphosphoric acid (ADP), A denosine monophosphoric acid (AMP).

The cytoplasm of each cell, as well as mitochondria, chloroplasts and nuclei, contains adenosine triphosphoric acid (ATP). It supplies energy for most of the reactions that occur in the cell. With the help of ATP, the cell synthesizes new molecules of proteins, carbohydrates, fats, carries out active transport of substances, and beats flagella and cilia.

ATP is similar in structure to the adenine nucleotide that is part of RNA, only instead of one phosphoric acid, ATP contains three phosphoric acid residues.

Structure of the ATP molecule:

The unstable chemical bonds that connect phosphoric acid molecules in ATP are very rich in energy. When these connections are broken, energy is released, which is used by each cell to support vital processes:

ATP ADP + P + E

ADP AMP + F + E,

where F is phosphoric acid H3PO4, E is the released energy.

Chemical bonds in ATP between phosphoric acid residues that are rich in energy are called macroergic connections. The cleavage of one molecule of phosphoric acid is accompanied by the release of energy - 40 kJ.

ATP is formed from ADP and inorganic phosphate due to the energy released during the oxidation of organic substances and during photosynthesis. This process is called phosphorylation.

In this case, at least 40 kJ/mol of energy must be expended, which is accumulated in high-energy bonds. Consequently, the main significance of the processes of respiration and photosynthesis is determined by the fact that they supply energy for the synthesis of ATP, with the participation of which most of the work is performed in the cell.

ATP is renewed extremely quickly. In humans, for example, each ATP molecule is broken down and regenerated 2,400 times a day, so that its average lifespan is less than 1 minute. ATP synthesis occurs mainly in mitochondria and chloroplasts (partially in the cytoplasm). The ATP formed here is sent to those parts of the cell where the need for energy arises.

ATP plays an important role in the bioenergetics of the cell: it performs one of the most important functions - an energy storage device, it is a universal biological energy accumulator.

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 monomeric units - nucleotides. The role of nucleic acids cannot be overestimated. The stability of their structure determines the normal functioning of the body, and any deviations in the structure inevitably lead to changes in cellular organization, the activity of physiological processes and the viability of cells in general.

The concept of a nucleotide and its properties

Each 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 during its life.

The main properties of these essential substances include:

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

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

Each nucleotide consists of:

Sugar residue;
. nitrogenous base;
. phosphate group or 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.

Nucleic acid composition

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

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

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

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

Species composition of nitrogenous bases

DNA nucleotides based on 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 belong to the class of pyrimidines. In terms of molecular weight, purines are always heavier than pyrimidines.

RNA nucleotides based on the nitrogenous base are represented by:

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

Uracil, like thymine, is a pyrimidine base.

In the scientific literature you can often find another designation for 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, are composed of 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) consist of a pyrimidine and an 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 produces 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.

Polynucleotide synthesis is a 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 a chain from only one end (3´) with a free hydroxy group.

DNA molecule structure

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

The sequence of nucleotides in a DNA chain determines its primary one; it is formed due to hydrogen bonds, the basis of which is the principle of complementarity. In other words, during the synthesis of a double chain, a certain pattern applies: adenine of one chain corresponds to 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 latter case hydrogen bonds. This connection of nucleotides ensures a strong connection of the chains and an equal distance between them.

Knowing the nucleotide sequence of one DNA strand, the second one can be completed using the principle of complementarity or addition.

The tertiary structure of DNA is formed due to complex three-dimensional bonds, which makes its molecule more compact and able to fit into a small cell volume. For example, the length of the DNA of E. coli 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 an RNA molecule

RNA is represented by a single polynucleotide chain formed between a pentose (in this case ribose) and a phosphate residue. It is much shorter in length than DNA. There are also differences in the species composition of nitrogenous bases in the nucleotide. In RNA, uracil is used instead of the pyrimidine base 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) - very diverse in nucleotide composition. Transfers genetic information from DNA to ribosomes and acts as a matrix for the synthesis of protein molecules.

The role of nucleotides in the body

Nucleotides in the cell perform a number of important functions:

Used as building 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 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.

Lecture No. 19
NUCLEOSIDES. NUCLEOTIDES. NUCLEIC ACIDS
Plan

1. Nucleic bases.
2. Nucleosides.
3. Nucleotides.
4. Nucleotide coenzymes.
5. Nucleic acids.

Lecture No. 19

NUCLEOSIDES. NUCLEOTIDES. NUCLEIN
ACIDS

Plan

1. Nucleic bases.
2. Nucleosides.
3. Nucleotides.
4. Nucleotide coenzymes.
5. Nucleic acids.

Nucleic acids – present in
cells of all living organisms are biopolymers that perform essential functions
on the storage and transmission of genetic information and participate in the mechanisms of its
implementation in the process of cellular protein synthesis.

Establishing the composition of nucleic acids by sequentially
hydrolytic cleavage allows us to identify the following structural
Components.

Let's consider the structural components of nucleic acids
acids in order of complexity of their structure.

1. Nucleic bases.

Heterocyclic bases included in the composition
nucleic acids ( nucleic bases), is a hydroxy- and
amino derivatives of pyrimidine and purine. Nucleic acids contain three
heterocyclic bases with a pyrimidine ring ( pyrimidine
grounds) and two - with the purine cycle (purine bases). Nucleic bases
have trivial names and corresponding one-letter designations.

In the composition of nucleic acids, heterocyclic
the bases are in the thermodynamically stable oxo form.

In addition to these groups of nucleic bases,
called main, in nucleic acids in small quantities
meet minor bases: 6-oxopurine (hypoxanthine),
3-N-methyluracil, 1-N-methylguanine, etc.

Nucleic acids include residues
monosaccharides – D-ribose and 2-deoxy –D-ribose. Both monosaccharides are present in
nucleic acids in b -furanose form.

2. Nucleosides.

Nucleosides are N-glycosides formed by nucleobases and ribose
or deoxyribose.

Between the anomeric carbon atom of the monosaccharide and the nitrogen atom at position 1
pyrimidine ring or the nitrogen atom at position 9 of the purine ring forms b -glycosidic
connection.

Depending on the nature of the monosaccharide residue
nucleosides are divided into ribonucleosides(contain a ribose residue) and deoxyribonucleosides(contain a deoxyribose residue). Titles
nucleosides are built on the basis of the trivial names of nucleic bases,
adding ending –idin for pyrimidine derivatives and -osin For
purine derivatives. The prefix is ​​added to the names of deoxyribonucleosides deoxy-. The exception is the nucleoside formed by thymine and
deoxyribose, to which the prefix deoxy- is not added because
thymine forms nucleosides with ribose only in very rare cases.

To designate nucleosides we use
single-letter designations of the nucleic bases included in their composition. TO
deoxyribonucleosides (with the exception of thymidine) are denoted by the letter
"d".

Along with the main
nucleosides in the composition of nucleic acids there are minor nucleosides,
containing modified nucleic acid bases (see above).

In nature, nucleosides are also found in
free state, mainly in the form of nucleoside antibiotics, which
exhibit antitumor activity. Nucleoside antibiotics have some
differences from ordinary nucleosides in the structure of either the carbohydrate part, or
heterocyclic base, which allows them to act as
antimetabolites, which explains their antibiotic activity.

Like N-glycosides, nucleosides are resistant to
alkalis, but are broken down by acids to form free
monosaccharide and nucleic base. Purine nucleosides are hydrolyzed
much lighter than pyrimidines.

3. Nucleotides

Nucleotides are esters of nucleosides and phosphorus
acids (nucleoside phosphates). The ester bond with phosphoric acid is formed by OH.
group in position 5/ or
3 / monosaccharide. Depending on the
the nature of the monosaccharide residue, nucleotides are divided into ribonucleotides(structural elements of RNA) and deoxyribonucleotides(structural elements
DNA). Nucleotide names include the name of the nucleoside and the position in
there is no phosphoric acid residue. Nucleoside abbreviations contain
designation of a nucleoside, a mono-, di- or triphosphoric acid residue, for
3 / -derivatives are also indicated
position of the phosphate group.

Nucleotides are monomeric units, from
which construct the polymer chains of nucleic acids. Some nucleotides
act as coenzymes and participate in metabolism.

4. Nucleotide
coenzymes

Coenzymes- these are organic compounds
non-protein nature, which are necessary for the implementation of catalytic
enzyme action. Coenzymes belong to different classes of organic
connections. An important group of coenzymes are nucleoside polyphosphates .

Adenosine phosphates – derivatives
adenosine containing residues of mono-, di- and triphosphoric acids. Special place
occupy adenosine-5/ -mono-, di- and
triphosphates - AMP, ADP and ATP - macroergic substances that have
large reserves of free energy in mobile form. The ATP molecule contains
high-energy P-O bonds, which are easily cleaved as a result of hydrolysis.
The free energy released in this case ensures the flow of conjugated
hydrolysis of ATP by thermodynamically unfavorable anabolic processes, for example,
protein biosynthesis.

Coenzyme A. The molecule of this
coenzyme consists of three structural components: pantothenic acid,
2-aminoethanethiol and ADP.

Coenzyme A is involved in the processes
enzymatic acylation, activating carboxylic acids by converting them
into reactive thiol esters.

Nicotinamide adenine dinucleotide coenzymes. Nicotinamide adenine dinucleotide (OVER +)and its phosphate ( NADP + ) contain the pyridinium cation in the form
nicotinamide fragment. Pyridinium cation in these coenzymes
capable of reversibly adding a hydride anion to form a reduced form
coenzyme - NAD N.

Thus, nicotinamide adenine dinucleotide
coenzymes are involved in redox processes associated with
transfer of hydride anion, for example, oxidation of alcohol groups into aldehyde groups
(conversion of retinol to retinal), reductive amination of keto acids,
reduction of keto acids to hydroxy acids. During these processes the substrate
loses (oxidation) or gains (reduction) two hydrogen atoms as
N+ and N - . The coenzyme serves as an acceptor
(ABOVE + ) or donor
(ABOVE . H) hydride ion. All processes with
involving coenzymes are stereoselective. So, when restoring
pyruvic acid produces exclusively L-lactic acid.

5. Nucleic acids.

Primary structure nucleic acid is a linear polymer chain built
of monomers - nucleotides that are linked to each other
3 / -5 / -phosphodiester
connections. The polynucleotide chain has a 5′ end and a 3′ end. At the 5′ end is
a phosphoric acid residue, and at the 3′ end there is a free hydroxyl group.
It is customary to write the nucleotide chain starting from the 5′ end.

Depending on the nature of monosaccharide residues
in a nucleotide there are deoxyribonucleic acids (DNA) and ribonucleic acids
acids (RNA). DNA and RNA also differ in the nature of their constituents.
nucleic bases: uracil is found only in RNA, thymine - only in
DNA composition.

Secondary structure DNA is a complex of two polynucleotide chains twisted to the right
around a common axis so that the carbohydrate-phosphate chains are on the outside, and
nucleic bases are directed inward ( Watson-Crick double helix).
The helix pitch is 3.4 nm, there are 10 nucleotide pairs per turn. Polynucleotide
the circuits are antiparallel, those.
Opposite the 3′ end of one chain is the 5′ end of the other chain. Two strands of DNA
are not identical in composition, but they complementary. This is expressed in
the fact that opposite adenine (A) in one chain there is always thymine (T) in the other
chains, and opposite guanine (G) there is always cytosine (C). Complementary
pairing of A with T and G with C is carried out due to hydrogen bonds. Between A and T
Two hydrogen bonds are formed, three between G and C.

The complementarity of DNA strands is
the chemical basis of the most important function of DNA - storage and transmission of genetic
information.

Types of RNA. There are three main known
types of cellular RNA: transfer RNA (tRNA), messenger RNA (mRNA) and ribosomal
RNA (rRNA). They differ in location in the cell, composition and size,
as well as functions. RNAs usually consist of one polynucleotide chain.
which in space develops in such a way that its individual sections
become complementary to each other (“stick together”) and form short
double-helical regions of the molecule, while other regions remain
single-stranded.

Messenger RNA perform the function of a matrix
protein synthesis in ribosomes.

Ribosomal RNA act as structural
components of ribosomes.

Transfer RNAs participate in
transportation a -amino acids from the cytoplasm into ribosomes and in the translation of nucleotide information
the sequence of mRNA into the sequence of amino acids in proteins.

Mechanism of transmission of genetic information. Genetic information encoded in nucleotide sequence
DNA. The mechanism for transmitting this information includes three main stages.

First stage - replication–copying
maternal DNA with the formation of two daughter DNA molecules, nucleotide
the sequence of which is complementary to the sequence of the maternal DNA and
is uniquely determined by it. Replication is carried out by synthesizing new
DNA molecules on the mother, which plays the role of a matrix. Double helix
maternal DNA unwinds and a new one is synthesized on each of the two strands
(daughter) DNA chain taking into account the principle of complementarity. The process is carried out
under the action of the enzyme DNA polymerase. Thus from the same maternal DNA
two daughter ones are formed, each of which contains one
mother and one newly synthesized polynucleotide chain.

Second phase - transcription– process, in
during which part of the genetic information is rewritten from DNA in the form of mRNA.
Messenger RNA is synthesized on a section of despiralized DNA strand as a template
under the action of the enzyme RNA polymerase. In the polynucleotide chain of mRNA
ribonucleotides carrying certain
nucleic bases are arranged in a sequence determined by
complementary interactions with the nucleic bases of the DNA chain. Wherein adenine base in DNA will correspond uracil base in RNA. Genetic information about protein synthesis is encoded in DNA with
with help triplet code. One amino acid is encoded
a sequence of three nucleotides called codon.
The section of DNA that encodes one polypeptide chain is called genome.
Each codon in DNA has a corresponding complementary codon in mRNA. Overall molecule
mRNA is complementary to a specific part of the DNA chain - a gene.

The processes of replication and transcription occur in
cell nucleus. Protein synthesis occurs in ribosomes. Synthesized mRNA
migrates from the nucleus into the cytoplasm to ribosomes, transferring genetic information to
site of protein synthesis.

Third stage – broadcast- process
implementation of genetic information carried by mRNA in the form of a sequence
nucleotides into the amino acid sequence of a synthesized protein. a -Amino acids necessary for
protein synthesis are transported to ribosomes via tRNA, with which they
bind by acylation 3 / -OH groups at the end of the tRNA chain.

tRNA has an anticodon branch containing
trinucleotide - anticodon, which corresponds to what it carries
amino acid. On the ribosome, tRNAs are attached at anticodon sites to
corresponding mRNA codons. Specificity of codon and anticodon docking
ensured by their complementarity. Between adjacent amino acids
a peptide bond is formed. In this way, a strictly defined
sequence of amino acids joining into proteins, encoded in
genes.