This article contains information about the elements of all nucleic acids, namely its monomers. Here you will find data on their structure, the diversity of existing species, etc.
Nucleic acid - what is it
The most important component of any plant, animal, bacterial and even viral cell is the nucleic acid, which is responsible for the transmission, reproduction and preservation of information of a hereditary type. Biopolymer compounds - nucleic acids - are created by encoding nucleotides. Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are nucleic acids. Nucleic acid monomers are nucleotides of 5 varieties, of which 3 are suitable for both dioxy- and ribonucleic acids, and the remaining nucleotides are different.
Variety of nucleic acids
DNA and RNA are representatives of nucleic acids, but the latter ribonucleic acid, in accordance with the functions for which it is intended in the cell, may have various titles, for example: transport ribonucleic acid (tRNA) or information ribonucleic acid (mRNA). However, this item does not affect the structural features of the to-you. What is a nucleic acid monomer? The answer to this question will be the enumeration of the elements: ribose and deoxyribose (types of sugars), HPO3 acid, or rather, its residues in the bases of thymine (uracil) and adenine, guanine and cytosine.
Monomers
Nucleic acid monomers are three components, as mentioned earlier, - this is a monosaccharide, holders of heterocyclic properties - nitrogenous bases and an acid residue HPO3. Composite types of nucleic acid monomers are purine derivatives of adenine (A) and guanine (G) and components of a pyrimidine nature: cytosines (C), thymines (T) and uracil (U). It is also worth knowing about the existence of atypical bases, which are represented by pseudouridines and dihydrouridines.
Nucleic acid monomers are substances responsible for vital functions, inherent in both prokaryotic and eukaryotic organisms. Nucleic acids are classified according to which monosaccharide the acid itself is. Ribose to-you are represented by ribose, and nucleic acids, represented by deoxyribose, are called deoxyribose. The dominant difference between RNA and DNA chains lies in the presence of either thymine or uracil in the chain of the molecule. DNA carries pyrimidine thymine, and RNA carries uracil. These two nucleotides are replaced in these acids and become complementary to adenine.
Nucleic acid monomers are compounds based on chemical bond- 3.5-phosphodiester, which forms linear structures, and its purpose is to bind the pentose in the nucleotide. This design of nucleic acids allows the formation of a free 3-OH group at one chain end and a 5-OH group at the opposite end of the chain.
RNA and DNA are universal and unique to all organisms. This is due to their ability to transmit and store a variety of information that carries genetic heredity. Almost every living organism simultaneously carries both acids, based on both the monosaccharide ribose and deoxyribose, and only viruses - representatives of a non-cellular life form - contain only one form of nucleic acid.
DNA is a polymer molecule consisting of thousands and even millions of monomers - deoxyribonucleotides (nucleotide). DNA is found predominantly in the nucleus of cells, as well as a small amount in mitochondria and chloroplasts.
RNA is a polymer whose monomer is a ribonucleotide. RNA is found in the nucleus and cytoplasm. RNA is a single-stranded molecule built in the same way as one of the DNA chains. The three bases are exactly the same DNA: A, G, C, but instead of the T present in DNA, RNA contains U. In RNA, instead of the deoxyribose carbohydrate, ribose is present.
^ 13: Nucleic acids: structure and function. Chemical structure of nucleic acid monomers (nucleotides and nucleosides, purines and pyrimidines).
Nucleic acids are linear polymers whose monomers are nucleotides. A nucleotide is formed by a nucleoside group, a phosphate, and a pentose. Polymers are macromolecules that are made up of a large number repeating structural units - monomers. DNA monomers are deoxyribonucleotides, RNA monomers are ribonucleotides.
^ Structure and nomenclature of nucleotides. A nucleotide consists of three components: phosphate - sugar - base.
carbohydrate component of a nucleotide represented by ribose or 2'-deoxyribose having a D-configuration.
^ Nitrogenous bases are heterocyclic organic compounds containing nitrogen atoms. DNA contains 4 types of bases - adenine (A), guanine (G), cytosine (C) and thymine (T), RNA includes A, G, C and U (uracil). Adenine and guanine are derivatives of purine, cytosine, thymine and uracil are pyrimidine derivatives.
Nomenclature. A compound consisting of a base and a carbohydrate is called a nucleoside. Nitrogenous bases are connected to the 1' carbon atom of the pentose by a β-glycosidic bond.
^ Primary Structure polymer is determined by the sequence of monomers in the chain. Nucleotides are connected to each other by a 3',5'-phosphodiester bond, forming polynucleotide chains of hundreds of thousands and millions of nucleotides. Short chains of ten to fifteen nucleotides are called oligonucleotides. The phosphate links the 3'-OH group of one nucleotide to the 5'-OH group of another nucleotide.
^ Genetic functions of nucleic acids:1-
storage of genetic information. 2
- implementation of genetic information (synthesis of a polypeptide). 3
- transmission of hereditary information to daughter cells during cell division and to subsequent generations during reproduction.
^ 14: Primary structure of DNA (structure and nomenclature of nucleotides, formation of a polynucleotide chain, direction of the chain, connection between nucleotides).
DNA is the genetic material of all cellular life forms, as well as a number of viruses. DNA performs all the functions of nucleic acids. DNA is characterized by a number of features: 1 - the ability to replicate. 2 - the ability to repair. 3 - ability to recombine.
Localization of DNA in the cell: prokaryotes - cytoplasm (nucleoid, plasmids). Eukaryotes - nucleus (chromosomes), organoids (mitochondria, plastids, cell center).
^ PRIMARY structure of DNA- this is a linear polymer - a chain of consecutive nucleotides (deoxyribonucleotide) connected by 3',5' phosphodiester bonds.
The composition of the deoxyribonucleotide includes one of the nitrogenous bases (A, G, T or C), a pentose - deoxyribose and a phosphate residue. Thus, deoxyribonucleotides differ only in nitrogenous bases.
Nucleotides are connected to each other by a 3',5'-phosphodiester bond, forming polynucleotide chains. Short chains of ten to fifteen nucleotides are called oligonucleotides. The phosphate links the 3'-OH group of one nucleotide to the 5'-OH group of another nucleotide.
The formation of the primary structure is provided by two types of bonds: glycosidic between the nitrogenous base and carbohydrate, and phosphodiester between nucleotides.
^15: Watson and Crick DNA model. Parameters and structure of the DNA double helix (principle of complementarity, hydrogen bonds and stacking interactions).
Secondary structure of DNA. The DNA molecule in prokaryotic and eukaryotic cells is present only in the form of a double helix, i.e. consists of two polynucleotide chains. These chains are complementary, antiparallel and twisted into a spiral around a common axis. There are 10 base pairs per turn of the helix, the diameter of the helix is 2 nm. The sugar-phosphate backbone is located outside (negatively charged), the nitrogenous bases are inside the helix and stacked one above the other. This DNA structure model was proposed by J. Watson and F. Crick in 1953.
^ Chargaff Rules. In 1953, Chargaff established the following patterns:
amount purine bases (A + G) in a DNA molecule is always equal to the number pyrimidine bases (T + C).
the amount of adenine is equal to the amount of thymine [A=T, A/T= 1]; the amount of guanine is equal to the amount of cytosine [G=C, G/C=1];
the ratio of the amount of guanine and cytosine in DNA to the amount of adenine and thymine is constant for each type of living organism: [(G+C)/(A+T)=K, where K is the specificity coefficient].
Chargaff's rules, as a rule, are carried out on the DNA double helix due to the complementarity of adenine to thymine, and guanine to cytosine. In some cases, the content of guanine is higher than that of cytosine due to the methylation of some cytosine residues in DNA.
^ Principle of complementarity. Nitrogenous bases in a DNA molecule can form canonical pairs: A - T, G - C. This means that hydrogen bonds and a DNA molecule are formed only between complementary bases: two are formed between adenine and thymine, three hydrogen bonds between guanine and cytosine.
^ DNA strands are antiparallel. Each strand of DNA has two ends, a 5' end and a 3' end. At the 5'-end of the polynucleotide chain, the 5-OH group of deoxyribose is not linked to another nucleotide; at the other end of the chain, the 3-OH group is also not linked to another nucleotide. The rule of antiparallelism means that two strands in a DNA molecule have opposite directions. By convention, the direction is taken as the direction of the chain 5’ → 3’ .
^ Rules for writing a DNA sequence: in the form of a sequence of letters denoting the bases: 5' - GATCCA - 3', or in the form of arrows with the opposite orientation.
Nucleic acids are high-molecular organic compounds, biopolymers formed by nucleotide residues. The polymeric forms of nucleic acids are called polynucleotides. Chains of nucleotides are connected through a phosphoric acid residue (phosphodiester bond). There are two classes of nucleic acids:
Deoxyribonucleic acid (DNA). Sugar - deoxyribose, nitrogenous bases: purine - guanine (G), adenine (A), pyrimidine thymine (T) and cytosine (C). DNA often consists of two polynucleotide strands directed antiparallel. 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.
Ribonucleic acid (RNA). Sugar - ribose, nitrogenous bases: purine - guanine (G), adenine (A), pyrimidine uracil (U) and cytosine (C). The structure of the polynucleotide chain is similar to that of DNA. Due to the characteristics of ribose, RNA molecules often have different secondary and tertiary structures, forming complementary regions between different strands.
The DNA molecule is formed by two polynucleotide chains spirally twisted around each other and together around an imaginary axis, i.e. is a double helix. 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.
The DNA monomer - nucleotide (deoxyribonucleotide) - consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose), 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.
A polynucleotide chain is formed as a result of nucleotide condensation reactions. In this case, a phosphoester bond arises between the 3 "-carbon of the deoxyribose residue of one nucleotide and the phosphoric acid residue of the other (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 against the adenine of one chain in the other chain, and cytosine is always located against 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 DNA strands are strictly ordered (adenine - thymine, guanine - cytosine) and selectively combine with each other is called the principle of complementarity. 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.
The function of DNA is the storage and transmission of hereditary information.
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. The RNA monomer - nucleotide (ribonucleotide) - consists of residues of three substances:
1) nitrogenous base,
2) a five-carbon monosaccharide (pentose),
3) phosphoric acid.
The nitrogenous bases of RNA also belong to the classes of pyrimidines and purines. Pyrimidine bases of RNA - uracil, cytosine, purine bases - adenine and guanine. The RNA nucleotide monosaccharide is represented by ribose. There are three types of RNA:
1) information (matrix) RNA - mRNA (mRNA),
2) transfer 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.
The value of nucleic acids: storage, transfer and inheritance of information about the structure of protein molecules. The stability of NK is the most important condition for the normal functioning of cells and whole organisms.
Thus, the nucleic acids DNA and RNA are present in the cells of all living organisms and perform the most important functions of storing, transmitting and implementing hereditary information.
Part B
Part A
EXAMPLES OF TASKS
A1. The monomers of DNA and RNA are
1) nitrogenous bases 3) amino acids
2) phosphate groups 4) nucleotides
A2. Messenger RNA function:
1) doubling information
2) removal of information from DNA
3) transport of amino acids to ribosomes
4) information storage
A3. Indicate the second DNA strand complementary to the first: ATT - GCC - TSH
1) UAA - TGG - AAC 3) UCC - GCC - ACG
2) TAA - CHG - AAC 4) TAA - UGG - UUTs
A4. Confirmation of the hypothesis that DNA is the genetic material of the cell is:
1) the number of nucleotides in a molecule
2) DNA personality
3) the ratio of nitrogenous bases (A \u003d T, G \u003d C)
4) ratio of DNA in gametes and somatic cells (1:2)
A5. The DNA molecule is capable of transmitting information due to:
1) nucleotide sequences
2) the number of nucleotides
3) the ability to self-doubling
4) spiralization of the molecule
A6. In which case is the composition of one of the RNA nucleotides correctly indicated?
1) thymine - ribose - phosphate
2) uracil - deoxyribose - phosphate
3) uracil - ribose - phosphate
4) adenine - deoxyribose - phosphate
IN 1. Select the features of the DNA molecule
1) Single chain molecule
2) Nucleotides - ATUC
3) Nucleotides - ATHC
4) Carbohydrate - ribose
5) Carbohydrate - deoxyribose
6) Capable of replication
IN 2. Select the functions characteristic of eukaryotic cell RNA molecules
1) distribution of hereditary information
2) transmission of hereditary information to the site of protein synthesis
3) transport of amino acids to the site of protein synthesis
4) initiation of DNA replication
5) formation of the ribosome structure
6) storage of hereditary information
C1. Establishing the structure of DNA made it possible to solve a number of problems. What, in your opinion, were these problems and how were they solved as a result of this discovery?
C2. Compare nucleic acids by composition and properties.
2.4. The structure of pro- and eukaryotic cells. The relationship of the structure and functions of the parts and organelles of the cell is the basis of its integrity
The main terms and concepts tested in the examination paper: Golgi apparatus, vacuole, cell membrane, cell theory, leukoplasts, mitochondria, cell organelles, plastids, prokaryotes, ribosomes, chloroplasts, chromoplasts, chromosomes, eukaryotes, nucleus.
Every cell is a system. This means that all its components are interconnected, interdependent and interact with each other. It also means that disruption of the activity of one of the elements of this system leads to changes and disruptions in the operation of the entire system. A collection of cells forms tissues, various tissues form organs, and organs, interacting and performing general function form organ systems. This chain can be continued further, and you can do it yourself. The main thing to understand is that any system has a certain structure, level of complexity and is based on the interaction of the elements that make it up. Below are reference tables that compare the structure and function of prokaryotic and eukaryotic cells, and also analyze their structure and function. Carefully analyze these tables, because in the examination papers quite often questions are asked that require knowledge of this material.
Especially DNA is quite well known in science. This is explained by the fact that they are the substances of the cell, on which the storage and transmission of its hereditary information depends. DNA, discovered back in 1868 by F. Miescher, is a molecule with pronounced acid properties. The scientist isolated it from the nuclei of leukocytes - cells immune system. Over the next 50 years, studies of nucleic acids were carried out sporadically, since most biochemists considered proteins to be the main organic substances responsible, among other things, for hereditary traits.
Since the decoding carried out by Watson and Crick in 1953, serious research began, which found out that deoxyribonucleic acid is a polymer, and nucleotides serve as DNA monomers. Their types and structure will be studied by us in this work.
Nucleotides as structural units of hereditary information
One of the fundamental properties of living matter is the preservation and transmission of information about the structure and functions of both the cell and the whole organism. This role is played by DNA monomers - nucleotides are a kind of "bricks" from which the unique structure of the substance of heredity is built. Let's consider what signs guided Live nature creating a nucleic acid supercoil.
How are nucleotides formed?
To answer this question, we need some knowledge from the field of chemistry. organic compounds. In particular, we recall that in nature there is a group of nitrogen-containing heterocyclic glycosides combined with monosaccharides - pentoses (deoxyribose or ribose). They are called nucleosides. For example, adenosine and other types of nucleosides are present in the cytosol of a cell. They enter into an esterification reaction with orthophosphoric acid molecules. The products of this process will be nucleotides. Each DNA monomer, and there are four types of them, has a name, for example, guanine, thymine and cytosine nucleotide.
Purine DNA monomers
In biochemistry, a classification has been adopted that divides DNA monomers and their structure into two groups: for example, adenine and guanine nucleotides are purine. They contain purine derivatives - organic matter having the formula C 5 H 4 N 4 . The DNA monomer, a guanine nucleotide, also contains a purine nitrogenous base connected to deoxyribose by an N-glycosidic bond in the beta configuration.
Pyrimidine nucleotides
The nitrogenous bases called cytidine and thymidine are derivatives of the organic substance pyrimidine. Its formula is C 4 H 4 N 2. The molecule is a six-membered planar heterocycle containing two nitrogen atoms. It is known that instead of a thymine nucleotide, molecules such as rRNA, tRNA, and mRNA contain a uracil monomer. In the process of transcription, during the writing off of information from the DNA gene to the mRNA molecule, the thymine nucleotide is replaced by adenine, and the adenine nucleotide is replaced by uracil in the synthesized mRNA chain. That is, the following record will be fair: A - U, T - A.
Chargaff's rule
In the previous section, we have already partially touched on the principles of correspondence between monomers in DNA chains and in the gene-mRNA complex. The famous biochemist E. Chargaff established a completely unique property of deoxyribonucleic acid molecules, namely, that the number of adenine nucleotides in it is always equal to thymine, and guanine - to cytosine. The main theoretical basis of Chargaff's principles was the research of Watson and Crick, who established which monomers form the DNA molecule and which spatial organization they have. Another pattern, derived by Chargaff and called the principle of complementarity, indicates the chemical relationship of purine and pyrimidine bases and their ability to form hydrogen bonds when interacting with each other. This means that the arrangement of monomers in both DNA strands is strictly determined: for example, opposite A of the first DNA strand, only T of the other can be located, and two hydrogen bonds arise between them. Opposite the guanine nucleotide, only cytosine can be located. In this case, three hydrogen bonds form between the nitrogenous bases.
The role of nucleotides in the genetic code
To carry out the protein biosynthesis reaction occurring in ribosomes, there is a mechanism for translating information about the amino acid composition of the peptide from the mRNA nucleotide sequence into the amino acid sequence. It turned out that three adjacent monomers carry information about one of the 20 possible amino acids. This phenomenon is called in problem solving. molecular biology it is used to determine both the amino acid composition of a peptide and to clarify the question: which monomers form a DNA molecule, in other words, what is the composition of the corresponding gene. For example, the AAA triplet (codon) in the gene encodes the amino acid phenylalanine in the protein molecule, and in the genetic code it will correspond to the UUU triplet in the mRNA chain.
Interaction of Nucleotides in the Process of DNA Replication
As it was found out earlier, structural units, DNA monomers are nucleotides. Their specific sequence in the chains is the template for the process of synthesis of the daughter molecule of deoxyribonucleic acid. This phenomenon occurs in the S-stage of cell interphase. The nucleotide sequence of the new DNA molecule is assembled on the parent chains under the action of the DNA polymerase enzyme, taking into account (A - T, D - C). Replication refers to reactions matrix synthesis. This means that the DNA monomers and their structure in the parent chains serve as the basis, that is, the matrix for its child copy.
Can the structure of a nucleotide change?
By the way, let's say that deoxyribonucleic acid is a very conservative structure of the cell nucleus. There is a logical explanation for this: the nucleus stored in the chromatin must be unchanged and copied without distortion. Well, the cellular genome is constantly "under the gun" of environmental factors. For example, such aggressive chemical compounds like alcohol, drug, radioactive radiation. All of them are so-called mutagens, under the influence of which any DNA monomer can change its chemical structure. Such a distortion in biochemistry is called a point mutation. The frequency of their occurrence in the cell genome is quite high. Mutations are corrected by the well-functioning work of the cellular repair system, which includes a set of enzymes.
Some of them, for example, restrictases, "cut out" damaged nucleotides, polymerases provide the synthesis of normal monomers, ligases "sew" the restored sections of the gene. If, for some reason, the mechanism described above does not work in the cell and the defective DNA monomer remains in its molecule, the mutation is picked up by the processes of matrix synthesis and phenotypically manifests itself in the form of proteins with impaired properties, unable to perform the necessary functions inherent in them in cellular metabolism. This is a serious negative factor that reduces the viability of the cell and shortens its lifespan.
