EntranceFunctions of DNA molecules. Structure and functions of DNA
In this article you can learn the biological role of DNA. So, this abbreviation is familiar to everyone since school, but not everyone has an idea what it is. After a school biology course, only minimal knowledge of genetics and heredity remains in the memory, since children are taught this complex topic only superficially. But this knowledge (the biological role of DNA, the effect it has on the body) can be incredibly useful.
Let's start with the fact that nucleic acids perform an important function, namely, they ensure the continuity of life. These macromolecules come in two forms:
- DNA (DNA);
- RNA (RNA).
They are transmitters of the genetic plan for the structure and functioning of the body's cells. Let's talk about them in more detail.
DNA and RNA
Let's start with what branch of science deals with such complex issues as:
- studying the principles of storage;
- its implementation;
- broadcast;
- study of the structure of biopolymers;
- their functions.
All this is studied by molecular biology. It is in this branch of biological sciences that one can find the answer to the question of what is the biological role of DNA and RNA.
These high molecular weight compounds formed from nucleotides are called “nucleic acids”. It is here that information about the body is stored, which determines the development of the individual, growth and heredity.
The discovery of deoxyribonucleic acid dates back to 1868. Then scientists were able to detect them in the nuclei of leukocytes and moose sperm. Subsequent research showed that DNA can be found in all plant and animal cells. The DNA model was presented in 1953, and the Nobel Prize for the discovery was awarded in 1962.
DNA
Let's start this section with the fact that there are 3 types of macromolecules:
- Deoxyribonucleic acid;
- ribonucleic acid;
- proteins.
Now we will take a closer look at the structure and biological role of DNA. So, this biopolymer transmits data about heredity, developmental characteristics not only of the carrier, but also of all previous generations. - nucleotide. Thus, DNA is the main component of chromosomes, containing the genetic code.
How is the transfer of this information possible? The whole point is the ability of these macromolecules to reproduce themselves. Their number is infinite, which can be explained by their large size, and as a consequence - by a huge number of various nucleotide sequences.
DNA structure
In order to understand the biological role of DNA in a cell, it is necessary to become familiar with the structure of this molecule.
Let's start with the simplest, all nucleotides in their structure have three components:
- nitrogenous base;
- pentose sugar;
- phosphate group.
Each individual nucleotide in a DNA molecule contains one nitrogenous base. It can be absolutely any of four possible:
- A (adenine);
- G (guanine);
- C (cytosine);
- T (thymine).
A and G are purines, and C, T and U (uracil) are pyramidins.
There are several rules for the ratio of nitrogenous bases, called Chargaff's rules.
- A = T.
- G = C.
- (A + G = T + C) we can move all the unknowns to the left side and get: (A + G)/(T + C) = 1 (this formula is the most convenient when solving problems in biology).
- A + C = G + T.
- The value (A + C)/(G + T) is constant. In humans it is 0.66, but, for example, in bacteria it is from 0.45 to 2.57.
The structure of each DNA molecule resembles a twisted double helix. Please note that the polynucleotide chains are antiparallel. That is, the arrangement of nucleotide pairs on one chain has the opposite sequence than on the other. Each turn of this helix contains as many as 10 nucleotide pairs.
How are these chains connected to each other? Why is the molecule strong and does not disintegrate? It's all about the hydrogen bond between nitrogenous bases (between A and T - two, between G and C - three) and hydrophobic interaction.
To conclude this section, I would like to mention that DNA is the largest organic molecules, the length of which varies from 0.25 to 200 nm.
Complementarity
Let's take a closer look at pair connections. We have already said that pairs of nitrogenous bases are not formed in a chaotic manner, but in a strict sequence. Thus, adenine can only bind to thymine, and guanine can only bind to cytosine. This sequential arrangement of pairs in one chain of the molecule dictates their arrangement in the other.
When replicating or doubling to form a new DNA molecule, this rule, called “complementarity,” must be observed. You can notice the following pattern, which was mentioned in the summary of Chargaff’s rules - the number of the following nucleotides is the same: A and T, G and C.
Replication
Now let's talk about the biological role of DNA replication. Let's start with the fact that this molecule has this unique ability to reproduce itself. This term refers to the synthesis of a daughter molecule.
In 1957, three models of this process were proposed:
- conservative (the original molecule is preserved and a new one is formed);
- semi-conservative (breaking the original molecule into monochains and adding complementary bases to each of them);
- dispersed (decay of the molecule, replication of fragments and collection in random order).
The replication process has three stages:
- initiation (unbraiding of DNA sections using the helicase enzyme);
- elongation (chain lengthening by adding nucleotides);
- termination (achieving the required length).
This complex process has a special function, that is, a biological role - ensuring the accurate transmission of genetic information.
RNA
We have told you what the biological role of DNA is, now we propose to move on to consideration (that is, RNA).
Let's start this section with the fact that this molecule is no less important than DNA. We can detect it in absolutely any organism, prokaryotic and eukaryotic cells. This molecule is even observed in some viruses (we are talking about RNA viruses).
A distinctive feature of RNA is the presence of a single chain of molecules, but, like DNA, it consists of four nitrogenous bases. In this case it is:
- adenine (A);
- uracil (U);
- cytosine (C);
- guanine (G).
All RNAs are divided into three groups:
- matrix, which is usually called informational (abbreviation is possible in two forms: mRNA or mRNA);
- ribosomal (rRNA).
Functions
Having understood the biological role of DNA, its structure and the characteristics of RNA, we propose to move on to the special missions (functions) of ribonucleic acids.
Let's start with mRNA or mRNA, the main task of which is to transfer information from the DNA molecule to the cytoplasm of the nucleus. Also, mRNA is a template for protein synthesis. As for the percentage of this type of molecules, it is quite low (about 4%).
And the percentage of rRNA in the cell is 80. They are necessary because they are the basis of ribosomes. Ribosomal RNA takes part in protein synthesis and polypeptide chain assembly.
The adapter that builds the amino acid chain is tRNA, which transfers amino acids to the area of protein synthesis. The percentage in the cell is about 15%.
Biological role
To summarize: what is the biological role of DNA? At the time of the discovery of this molecule, they could not provide obvious information on this matter, but even now not everything is known about the significance of DNA and RNA.
If we talk about general biological significance, then their role is to transfer hereditary information from generation to generation, protein synthesis and coding of protein structures.
Many people also express this version: these molecules are connected not only with the biological, but also with the spiritual life of living beings. According to metaphysicians, DNA contains past life experiences and divine energy.
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
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, 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. 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 transfer of hereditary information from the mother cell to the daughter cells and all subsequent ones.
14 . Ribonucleic acids, their types, structure, purpose.
RNA- a class of nucleic acids, linear polymers of nucleotides, which include a phosphoric acid residue, ribose (unlike DNA containing deoxyribose) and nitrogenous bases - adenine, cytosine, guanine, uracil (unlike DNA, containing thymine instead of uracil). These molecules are found in the cells of all living organisms, as well as in some viruses. RNA is found mainly in the cytoplasm of cells . These molecules are synthesized in the cells of all cellular living organisms and are also found in viroids and some viruses. Basic functions of RNA in cellular organisms, it is a template for translating genetic information into proteins and supplying the corresponding amino acids to ribosomes. In viruses, it is a carrier of genetic information (encodes envelope proteins and viral enzymes). RNA structure.
The molecule has a single-strand structure. Polymer. As a result of the interaction of nucleotides with each other, the RNA molecule acquires a secondary structure of various shapes (helix, globule, etc.). The monomer of RNA is a nucleotide (a molecule containing a nitrogenous base, a phosphoric acid residue and a sugar (peptose)). RNA is similar in structure to one strand of DNA. Nucleotides that make up RNA: guanine, adenine, cytosine, uracil. Adenine and guanine are purine bases, cytosine and uracil are pyrimidine bases. Unlike the DNA molecule, the carbohydrate component of ribonucleic acid is not deoxyribose, but ribose. The second significant difference in the chemical structure of RNA from DNA is the absence of a nucleotide such as thymine in the ribonucleic acid molecule. In RNA it is replaced by uracil.
Types and types of RNA cells.
There are three types of RNA, each with a specific role in protein synthesis.
1. Messenger RNA transfers the genetic code from the nucleus to the cytoplasm, thus determining the synthesis of various proteins.
2. Transfer RNA transfers activated amino acids to ribosomes for the synthesis of polypeptide molecules.
3. Ribosomal RNA in combination with approximately 75 different proteins, it forms ribosomes - cellular organelles on which polypeptide molecules are assembled.
Messenger RNA is a long single-chain molecule present in the cytoplasm. This RNA molecule contains from several hundred to several thousand RNA nucleotides, forming codons strictly complementary to DNA triplets.
Another type of RNA that plays a critical role in protein synthesis is called transfer RNA, since it transports amino acids to the protein molecule under construction. Each transfer RNA specifically binds to only one of the 20 amino acids that make up protein molecules. Transfer RNAs act as carriers of specific amino acids, delivering them to ribosomes on which polypeptide molecules are assembled.
Each specific transfer RNA recognizes its “own” codon of the messenger RNA attached to the ribosome and delivers the corresponding amino acid to the corresponding position in the synthesized polypeptide chain. The transfer RNA strand is much shorter than messenger RNA, contains only about 80 nucleotides, and is packaged in a cloverleaf shape. At one end of the transfer RNA there is always adenosine monophosphate (AMP), to which the transported amino acid is attached through the hydroxyl group of ribose. Transfer RNAs serve to attach specific amino acids to the polypeptide molecule under construction; therefore, it is necessary that each transfer RNA has specificity for the corresponding codons of the messenger RNA. The code by which transfer RNA recognizes the corresponding codon on the messenger RNA is also a triplet and is called an anticodon. The anticodon is located approximately in the middle of the transfer RNA molecule. During protein synthesis, the nitrogenous bases of the transfer RNA anticodon are attached via hydrogen bonds to the nitrogenous bases of the messenger RNA codon. Thus, on the messenger RNA, various amino acids are lined up in a certain order, one after another, forming the corresponding amino acid sequence of the synthesized protein.
Remember!
Why are nucleic acids classified as heteropolymers?
They consist of different monomers - nucleotides, but the nucleotides themselves differ from each other in some structures.
What is a nucleic acid monomer?
Nucleotides
What functions of nucleic acids do you know?
Storage and transmission of hereditary information. DNA contains information about the primary structure of all proteins needed by the body. This information is recorded in a linear sequence of nucleotides. Since proteins play a primary role in the life of the body, participating in the structure, development, and metabolism, it can be argued that DNA stores information about the body. In RNA, each type performs its own function depending on its structure. m-RNA is a copy of a DNA section where information about the number, composition and sequence of amino acid residues that determine the structure and functions of the protein molecule is recorded. This RNA contains the blueprint for constructing a polypeptide molecule. tRNA - its role is to attach an amino acid molecule and transport it to the site of protein synthesis. r-RNA - combines with protein and forms special organelles - ribosomes, on which protein molecules are assembled in the cell of any living organism.
What properties of living things are determined directly by the structure and functions of nucleic acids?
Heredity, variability, reproduction
Review questions and assignments
1. What are nucleic acids? Why did they get this name?
Nucleic acids are biopolymers whose monomers are nucleotides. From lat. “nucleos” - nucleus, since these acids are located or synthesized in the nucleus, or in prokaryotes, the function of nuclear information is performed by a nucleoid (DNA or RNA).
2. What types of nucleic acids do you know?
DNA, RNA: i-RNA, t-RNA, r-RNA.
4. Name the functions of DNA. How are the structure and functions of DNA interrelated?
Storage and transmission of hereditary information - DNA is located strictly in the nucleus.
The DNA molecule is capable of self-reproduction by duplication. Under the action of enzymes, the DNA double helix unwinds, and the bonds between nitrogenous bases are broken.
DNA contains information about the primary structure of all proteins needed by the body. This information is recorded in a linear sequence of nucleotides.
Since proteins play a primary role in the life of the body, participating in the structure, development, and metabolism, it can be argued that DNA stores information about the body.
5. What types of RNA exist in the cell where they are synthesized? List their functions.
i-RNA, t-RNA, r-RNA.
mRNA - synthesized in the nucleus on a DNA matrix and is the basis for protein synthesis.
tRNA - transport of amino acids to the site of protein synthesis - to ribosomes.
r-RNA is synthesized in the nucleoli of the nucleus and forms the ribosomes of the cell themselves.
All types of RNA are synthesized on a DNA template.
6. Is it enough to know which monosaccharide is part of the nucleotides to understand what kind of nucleic acid we are talking about?
Yes, RNA contains ribose.
DNA contains deoxyribose.
It will not be possible to recognize RNA types by one monosaccharide.
7. A fragment of one DNA strand has the following composition: A-G-C-G-C-C-C-T-A-. Using the principle of complementarity, complete the second chain.
A-G-C-G-C-C-C-T-A
T-C-G-C-G- G-G-A-T
Think! Remember!
1. Why are there three types of RNA molecules in cells, but only one type of DNA?
DNA is the largest molecule; it cannot leave the nucleus; the pores are small. RNA is small molecules, each performing its own function, providing different functions in the cell while working simultaneously. Many types of RNA can be synthesized simultaneously on the DNA matrix, and they all go to perform their functions.
3. What types of RNA will be the same in all organisms? Which type of RNA has the greatest variability? Explain your point of view.
i-RNA and t-RNA will be the same in all organisms, since protein biosynthesis follows a single mechanism, and t-RNA carries the same 20 amino acids. rRNA may be different.
1. Select examples of the functions proteins perform at the cellular level of life.
1) provide transport of ions across the membrane
2) are part of hair, feathers
3) form the skin
4) antibodies bind antigens
5) store oxygen in muscles
6) ensure the operation of the fission spindle
2. Select RNA features.
1) found in ribosomes and the nucleolus
2) capable of replication
3) consists of one chain
4) contained in chromosomes
5) set of ATGC nucleotides
6) set of nucleotides AGCU
3. What functions do lipids perform in the animal body?
1) enzymatic
2) storing
3) energy
4) structural
5) contractile
6) receptor
4. What functions do carbohydrates perform in the animal body?
1) catalytic
2) structural
3) storing
4) hormonal
5) contractile
6) energy
5. Proteins, unlike nucleic acids,
1) participate in the formation of the plasma membrane
2) are part of chromosomes
3) participate in humoral regulation
4) carry out a transport function
5) perform a protective function
6) transfer hereditary information from the nucleus to the ribosome
6. Which of the following proteins cannot be detected inside a muscle cell?
2) hemoglobin
3) fibrinogen
5) RNA polymerase
6) trypsin
7. Select the structural features of protein molecules.
1) consist of fatty acids
2) consist of amino acids
3) the monomers of the molecule are held together by peptide bonds
4) consist of monomers of the same structure
5) are polyhydric alcohols
6) the quaternary structure of molecules consists of several globules
8. Select three functions that are unique to proteins.
1) energy
2) catalytic
3) motor
4) transport
5) structural
6) storage
9. What functions do carbohydrate and lipid molecules perform in a cell?
1) informational
2) catalytic
3) construction
4) energy
5) storing
6) motor
10. All of the chemical elements listed below, except two, are organogens. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) hydrogen
5) oxygen
11. All but two of the chemical elements listed below are macroelements. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
12. Select THREE functions of DNA in a cell
1) an intermediary in the transfer of hereditary information
2) storage of hereditary information
3) coding of amino acids
4) matrix for mRNA synthesis
5) regulatory
6) chromosome structuring
13. DNA molecule
1) a polymer whose monomer is a nucleotide
2) a polymer whose monomer is an amino acid
3) double-chain polymer
4) single chain polymer
5) contains hereditary information
6) performs an energy function in the cell
14. What features are characteristic of a DNA molecule?
1) consists of one polypeptide strand
2) consists of two polynucleotide strands twisted into a spiral
3) has a nucleotide containing uracil
4) has a nucleotide containing thymine
5) preserves hereditary information
6) transfers information about the structure of the protein from the nucleus to the ribosome
15. Monosaccharides in the cell perform the following functions:
1) energy
2) constituent components of polymers
3) informational
4) constituent components of nucleic acids
5) protective
6) transport
16. How is an mRNA molecule different from DNA?
1) transfers hereditary information from the nucleus to the ribosome
2) nucleotides include residues of nitrogenous bases, carbohydrates and phosphoric acid
3) consists of one polynucleotide strand
4) consists of two polynucleotide strands interconnected
5) it contains the carbohydrate ribose and the nitrogenous base uracil
6) it contains the carbohydrate deoxyribose and the nitrogenous base thymine
17. All but two of the following features are functions of lipids. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) storing
2) hormonal
3) enzymatic
4) carrier of hereditary information
5) energy
18. All of the signs below, except two, can be used to describe the significance of proteins in the human and animal body. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) serve as the main building material
2) are broken down in the intestines to glycerol and fatty acids
3) are formed from amino acids
4) in the liver they are converted into glycogen
5) as enzymes they accelerate chemical reactions
19. All but two of the features listed below can be used to describe a DNA molecule. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
4) capable of self-doubling
5) in combination with proteins forms chromosomes
20. All but two of the following features can be used to determine the functions of lipids in a cell. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) storage
2) regulatory
3) transport
4) enzymatic
5) construction
21. All but two of the following features can be used to describe the functions of nucleic acids in a cell. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) carry out homeostasis
2) transfer hereditary information from the nucleus to the ribosome
3) participate in protein biosynthesis
4) are part of the cell membrane
5) transport amino acids
22. All but two of the features listed below can be used to describe a DNA molecule. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated in the table.
1) consists of two chains forming a spiral
2) contains ATGC nucleotides
3) contains ribose sugar
4) self-doubling
5) participates in the broadcast process
23. All but two of the features listed below can be used to describe the insulin molecule. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table
1) consists of amino acids
2) adrenal hormone
3) a catalyst for many chemical reactions
4) pancreatic hormone
5) a substance of protein nature
24 All but two of the following characteristics can be used to describe egg white albumin. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) consists of amino acids
2) digestive enzyme
3) denatures reversibly when boiling eggs
4) monomers are connected by peptide bonds
5) the molecule forms primary, secondary and tertiary structures
25. All but two of the features listed below can be used to describe an RNA molecule. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated in the table.
1) consists of two polynucleotide chains twisted into a spiral
2) transfers information to the site of protein synthesis
3) in combination with proteins, builds the body of the ribosome
4) capable of self-doubling
5) transports amino acids to the site of protein synthesis
26. All but two of the characteristics listed below can be used to describe a starch molecule. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated in the table.
1) consists of one chain
2) dissolves well in water
3) in combination with proteins forms a cell wall
4) undergoes hydrolysis
5) is a reserve substance in muscle cells
The structure and properties of DNA determine its main functions:
1. Storage of genetic information. DNA is located in the nucleus and is excluded from active metabolic processes.
2. Transfer of genetic information offspring occurs through the process of mitosis and meiosis based on DNA replication.
3. Recording genetic information. Genetic information is written in the form GENETIC or biochemical code.
4 . Control behind the metabolism in the cell
Ribonucleic acids (RNA)
There are several types of RNA: ribosomal, messenger (template), transport, etc. They have different sizes, structures and functions.
Ribosomal RNA(rRNA) has a molecular weight of 1-2 million, the number of nucleotides is up to 5000. It is about 85% from all RNA. rRNA is not uniform in composition. In eukaryotic cells, rRNA synthesis is localized in nucleolus and is carried out by RNA polymerase I. Ribosomal genes are localized on chromosomes that have a secondary constriction. Ribosomal RNA is not translated and performs the following functions:
1 .is a structural component of the ribosome 2. responsible for interaction with mRNA and tRNA
Messenger RNA(mRNA or mRNA) is about 5% of all cellular RNA in eukaryotes. It is formed on unique sections of the DNA chain and carries information about the structural and regulatory proteins of the body. Depending on the degree of complexity, mRNA comes in different sizes (1-3 thousand nucleotides) and mass.
Bacterial mRNA differs in the number of proteins it encodes. Some mRNAs correspond to only one gene, while others (the majority) correspond to several genes.
In the composition of RNA, two types of regions can be distinguished: coding and non-coding. Coding ones determine the primary structure of the protein. Non-coding ones are located on 5’ - end (leader) and at 3’ - end (end or trailer)
IN 5" -terminal sequence contains a region necessary for binding mRNA With ribosome. Mature mRNA in eukaryotes 5" end carries a “cap” or CEP (methylated guanosine), on 3" end there is a polyadenylic “tail” (formed by 100-200 adenylic acid residues).
Fig.24. Structure of eukaryotic mRNA
CEP functions:
1 . protects mRNA from degradation;
2. responsible for attaching mRNA to the small subunit of the ribosome
3. increases the efficiency of mRNA translation in eukaryotes
Poly(A) functions:
1. protecting mRNA from degradation
2. it ensures the release of mRNA from the nucleus into the cytoplasm
3. the length of time the mRNA remains in the cytoplasm is determined by its length (the shorter the “tail,” the more time the mRNA remains in the cytoplasm)
4. provides the possibility of repeated translation of mRNA. After the act of translation, one or more nucleotides are cleaved from its 3" end.
5. participates in the process of mRNA maturation
Thus, the mRNA serves as a matrix for the synthesis of cellular proteins, i.e. she performs role as an intermediary between DNA and protein. It carries information about the time, quantity, place and conditions of synthesis of this protein, as well as the lifetime and degradation of itself (most often this information is programmed by specific sequences in the 3" untranslated region). Certain cell proteins recognize these sequences and bind to them and stabilize mRNA. mRNA exits through the pores of the nucleus into the cytoplasm. In the cytoplasm it can accumulate in an inactive form, i.e. infosomes, in which mRNA is in complex with proteins (Fig. 25).
Fig.25. The structure of the informationosome.
They were discovered in 1964 in the laboratory A.S. Spirina. It is now well established that “spare” mRNAs in embryonic cells are not immediately translated, but are stored for use at later stages of embryogenesis and play an important role in cell differentiation. Informosomes can be stored in the cytoplasm for a long time and used by the cell as needed. Their existence has been proven in eggs. Thus, when certain areas of the egg cytoplasm were irradiated with a laser beam, the formation of primary germ cells was disrupted, because Informosomes containing information about regulatory proteins responsible for the specialization of primordial germ cells were destroyed.
Thus, this form of existence of RNA is directly related to the regulation of translation in the ribosomal apparatus of the cell.
Transfer RNA(tRNA) is about 10% of all cellular RNA (Fig. 26). Its molecular weight is approximately 10,000. Its structure is the most studied compared to other classes of RNA. TRNA is synthesized in eukaryotes by RNA polymerase III as precursors. The structure of tRNA molecules is evolutionarily conserved, which is apparently due to their high degree of functional specialization. Mature tRNA has 75-85 nucleotides. On 5" end she always has guanine, on 3" - CCA triplet. Primary structure of tRNA - single chain of nucleotides. Secondary resembles a clover leaf with four helical sections - “hairpins”, where complementary nucleotides are paired: A - U, G - C. At the ends of the “hairpins” there are single-stranded loops. Tertiary structure tRNA arises from the folding of lateral hairpins and the interaction of additional bases. Resembles the shape of the Latin letter L.
Located in the bottom loop anticodon- a triplet that interacts with the complementary codon of mRNA (Fig. 26.). The amino acid attaches to the terminal adenosine at the 3" end (acceptor end).
Thus, tRNA performs two functions: 1. mRNA codon decoding; 2. Decoding and transfer of the corresponding amino acid.
Fig.26. Secondary and tertiary structure of tRNA. (B. Alberts et al., 1994, vol. 1, p. 60)
Low molecular weight RNA(nmRNAs or snRNAs) are diverse in function, structure and size. nmRNAs are also found in the nucleus and cytoplasm of eukaryotes as part of ribonucleoprotein particles (RNP particles), which play an important role in the mechanism splicing mRNA, in protein synthesis secreted by the cell. Some enzymes (e.g. isomerase, amylase, pancreatic ribonuclease) contain nmRNA as an essential structural element.
Heterogeneous nuclear RNA(hnRNA) – a mixture of transcripts of many nuclear genes; localized in the nucleus.
In most organisms, all RNAs act as intermediaries between DNA and cell structures. Only in some viruses and bacteriophages does RNA play a role primary information system.