Biosynthesis of protein and nucleic acids. Genes, genetic code

Previously, we emphasized that nucleotides have an important feature for the formation of life on Earth - in the presence of one polynucleotide chain in a solution, the process of formation of a second (parallel) chain spontaneously occurs based on the complementary connection of related nucleotides. The same number of nucleotides in both chains and their chemical affinity are an indispensable condition for the implementation of this type of reaction. However, during protein synthesis, when information from mRNA is implemented into the protein structure, there can be no talk of observing the principle of complementarity. This is due to the fact that in mRNA and in the synthesized protein not only the number of monomers is different, but also, what is especially important, there is no structural similarity between them (nucleotides on the one hand, amino acids on the other). It is clear that in this case there is a need to create a new principle for accurately translating information from a polynucleotide into the structure of a polypeptide. In evolution, such a principle was created and its basis was the genetic code.

The genetic code is a system for recording hereditary information in nucleic acid molecules, based on a certain alternation of nucleotide sequences in DNA or RNA, forming codons corresponding to amino acids in a protein.

The genetic code has several properties.

Tripletity.

Degeneracy or redundancy.

Unambiguity.

Polarity.

Non-overlapping.

Compactness.

Versatility.

It should be noted that some authors also propose other properties of the code related to the chemical characteristics of the nucleotides included in the code or the frequency of occurrence of individual amino acids in the body’s proteins, etc. However, these properties follow from those listed above, so we will consider them there.

A. Tripletity. The genetic code, like many complexly organized systems, has the smallest structural and smallest functional unit. A triplet is the smallest structural unit of the genetic code. It consists of three nucleotides. A codon is the smallest functional unit of the genetic code. Typically, triplets of mRNA are called codons. In the genetic code, a codon performs several functions. Firstly, its main function is that it encodes a single amino acid. Secondly, the codon may not code for an amino acid, but, in this case, it performs another function (see below). As can be seen from the definition, a triplet is a concept that characterizes elementary structural unit genetic code (three nucleotides). Codon – characterizes elementary semantic unit genome - three nucleotides determine the attachment of one amino acid to the polypeptide chain.

The elementary structural unit was first deciphered theoretically, and then its existence was confirmed experimentally. Indeed, 20 amino acids cannot be encoded with one or two nucleotides because there are only 4 of the latter. Three out of four nucleotides give 4 3 = 64 variants, which more than covers the number of amino acids available in living organisms (see Table 1).

The 64 nucleotide combinations presented in table have two features. Firstly, of the 64 triplet variants, only 61 are codons and encode any amino acid; they are called sense codons. Three triplets do not encode

Table 1.

Messenger RNA codons and corresponding amino acids

FOUNDATION OF KODONOV




	Nonsense	Nonsense
	Nonsense




		Meth



		Shaft

amino acids a are stop signals indicating the end of translation. There are three such triplets - UAA, UAG, UGA, they are also called “meaningless” (nonsense codons). As a result of a mutation, which is associated with the replacement of one nucleotide in a triplet with another, a nonsense codon can arise from a sense codon. This type of mutation is called nonsense mutation. If such a stop signal is formed inside the gene (in its information part), then during protein synthesis in this place the process will be constantly interrupted - only the first (before the stop signal) part of the protein will be synthesized. A person with this pathology will experience a lack of protein and will experience symptoms associated with this deficiency. For example, this kind of mutation was identified in the gene encoding the hemoglobin beta chain. A shortened inactive hemoglobin chain is synthesized, which is quickly destroyed. As a result, a hemoglobin molecule devoid of a beta chain is formed. It is clear that such a molecule is unlikely to fully fulfill its duties. A serious disease occurs that develops as hemolytic anemia (beta-zero thalassemia, from the Greek word “Thalas” - Mediterranean Sea, where this disease was first discovered).

The mechanism of action of stop codons differs from the mechanism of action of sense codons. This follows from the fact that for all codons encoding amino acids, corresponding tRNAs have been found. No tRNAs were found for nonsense codons. Consequently, tRNA does not take part in the process of stopping protein synthesis.

CodonAUG (sometimes GUG in bacteria) not only encode the amino acids methionine and valine, but are alsobroadcast initiator .

b. Degeneracy or redundancy.

61 of the 64 triplets encode 20 amino acids. This three-fold excess of the number of triplets over the number of amino acids suggests that two coding options can be used in the transfer of information. Firstly, not all 64 codons can be involved in encoding 20 amino acids, but only 20 and, secondly, amino acids can be encoded by several codons. Research has shown that nature used the latter option.

His preference is obvious. If out of 64 variant triplets only 20 were involved in encoding amino acids, then 44 triplets (out of 64) would remain non-coding, i.e. meaningless (nonsense codons). Previously, we pointed out how dangerous it is for the life of a cell to transform a coding triplet as a result of mutation into a nonsense codon - this significantly disrupts the normal functioning of RNA polymerase, ultimately leading to the development of diseases. Currently, three codons in our genome are nonsense, but now imagine what would happen if the number of nonsense codons increased by about 15 times. It is clear that in such a situation the transition of normal codons to nonsense codons will be immeasurably higher.

A code in which one amino acid is encoded by several triplets is called degenerate or redundant. Almost every amino acid has several codons. Thus, the amino acid leucine can be encoded by six triplets - UUA, UUG, TSUU, TsUC, TsUA, TsUG. Valine is encoded by four triplets, phenylalanine by two and only tryptophan and methionine encoded by one codon. The property that is associated with recording the same information with different symbols is called degeneracy.

The number of codons designated for one amino acid correlates well with the frequency of occurrence of the amino acid in proteins.

And this is most likely not accidental. The higher the frequency of occurrence of an amino acid in a protein, the more often the codon of this amino acid is represented in the genome, the higher the likelihood of its damage by mutagenic factors. Therefore, it is clear that a mutated codon has a greater chance of encoding the same amino acid if it is highly degenerate. From this perspective, the degeneracy of the genetic code is a mechanism that protects the human genome from damage.

It should be noted that the term degeneracy is used in molecular genetics in another sense. Thus, the bulk of the information in a codon is contained in the first two nucleotides; the base in the third position of the codon turns out to be of little importance. This phenomenon is called “degeneracy of the third base.” The latter feature minimizes the effect of mutations. For example, it is known that the main function of red blood cells is to transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. This function is performed by the respiratory pigment - hemoglobin, which fills the entire cytoplasm of the erythrocyte. It consists of a protein part - globin, which is encoded by the corresponding gene. In addition to protein, the hemoglobin molecule contains heme, which contains iron. Mutations in globin genes lead to the appearance of different variants of hemoglobins. Most often, mutations are associated with replacing one nucleotide with another and the appearance of a new codon in the gene, which may encode a new amino acid in the hemoglobin polypeptide chain. In a triplet, as a result of mutation, any nucleotide can be replaced - the first, second or third. Several hundred mutations are known that affect the integrity of the globin genes. Near 400 of which are associated with the replacement of single nucleotides in a gene and the corresponding amino acid replacement in a polypeptide. Of these only 100 replacements lead to instability of hemoglobin and various kinds of diseases from mild to very severe. 300 (approximately 64%) substitution mutations do not affect hemoglobin function and do not lead to pathology. One of the reasons for this is the above-mentioned “degeneracy of the third base,” when a replacement of the third nucleotide in a triplet encoding serine, leucine, proline, arginine and some other amino acids leads to the appearance of a synonymous codon encoding the same amino acid. Such a mutation will not manifest itself phenotypically. In contrast, any replacement of the first or second nucleotide in a triplet in 100% of cases leads to the appearance of a new hemoglobin variant. But even in this case, there may not be severe phenotypic disorders. The reason for this is the replacement of an amino acid in hemoglobin with another one similar to the first in physicochemical properties. For example, if an amino acid with hydrophilic properties is replaced by another amino acid, but with the same properties.

Hemoglobin consists of the iron porphyrin group of heme (oxygen and carbon dioxide molecules are attached to it) and protein - globin. Adult hemoglobin (HbA) contains two identical -chains and two -chains. Molecule -chain contains 141 amino acid residues, -chain - 146, - And -chains differ in many amino acid residues. The amino acid sequence of each globin chain is encoded by its own gene. Gene encoding -the chain is located in the short arm of chromosome 16, -gene - in the short arm of chromosome 11. Substitution in the gene encoding -the hemoglobin chain of the first or second nucleotide almost always leads to the appearance of new amino acids in the protein, disruption of hemoglobin functions and serious consequences for the patient. For example, replacing “C” in one of the triplets CAU (histidine) with “Y” will lead to the appearance of a new triplet UAU, encoding another amino acid - tyrosine. Phenotypically this will manifest itself in a severe disease.. A similar substitution in position 63 -chain of histidine polypeptide to tyrosine will lead to destabilization of hemoglobin. The disease methemoglobinemia develops. Replacement, as a result of mutation, of glutamic acid with valine in the 6th position -chain is the cause of the most severe disease - sickle cell anemia. Let's not continue the sad list. Let us only note that when replacing the first two nucleotides, an amino acid with physicochemical properties similar to the previous one may appear. Thus, replacement of the 2nd nucleotide in one of the triplets encoding glutamic acid (GAA) in -chain with “U” leads to the appearance of a new triplet (GUA), encoding valine, and replacing the first nucleotide with “A” forms the triplet AAA, encoding the amino acid lysine. Glutamic acid and lysine are similar in physicochemical properties - they are both hydrophilic. Valine is a hydrophobic amino acid. Therefore, replacing hydrophilic glutamic acid with hydrophobic valine significantly changes the properties of hemoglobin, which ultimately leads to the development of sickle cell anemia, while replacing hydrophilic glutamic acid with hydrophilic lysine changes the function of hemoglobin to a lesser extent - patients develop a mild form of anemia. As a result of the replacement of the third base, the new triplet can encode the same amino acids as the previous one. For example, if in the CAC triplet uracil was replaced by cytosine and a CAC triplet appeared, then practically no phenotypic changes will be detected in humans. This is understandable, because both triplets code for the same amino acid – histidine.

In conclusion, it is appropriate to emphasize that the degeneracy of the genetic code and the degeneracy of the third base from a general biological point of view are protective mechanisms that are inherent in evolution in the unique structure of DNA and RNA.

V. Unambiguity.

Each triplet (except nonsense) encodes only one amino acid. Thus, in the direction codon - amino acid the genetic code is unambiguous, in the direction amino acid - codon it is ambiguous (degenerate).

Unambiguous

Amino acid codon

Degenerate

And in this case, the need for unambiguity in the genetic code is obvious. In another option, when translating the same codon, different amino acids would be inserted into the protein chain and, as a result, proteins with different primary structures and different functions would be formed. Cell metabolism would switch to the “one gene – several polypeptides” mode of operation. It is clear that in such a situation the regulatory function of genes would be completely lost.

g. Polarity

Reading information from DNA and mRNA occurs only in one direction. Polarity is important for defining higher order structures (secondary, tertiary, etc.). Earlier we talked about how lower-order structures determine higher-order structures. Tertiary structure and higher order structures in proteins are formed as soon as the synthesized RNA chain leaves the DNA molecule or the polypeptide chain leaves the ribosome. While the free end of an RNA or polypeptide acquires a tertiary structure, the other end of the chain continues to be synthesized on DNA (if RNA is transcribed) or a ribosome (if a polypeptide is transcribed).

Therefore, the unidirectional process of reading information (during the synthesis of RNA and protein) is essential not only for determining the sequence of nucleotides or amino acids in the synthesized substance, but for the strict determination of secondary, tertiary, etc. structures.

d. Non-overlapping.

The code may be overlapping or non-overlapping. Most organisms have a non-overlapping code. Overlapping code is found in some phages.

The essence of a non-overlapping code is that a nucleotide of one codon cannot simultaneously be a nucleotide of another codon. If the code were overlapping, then the sequence of seven nucleotides (GCUGCUG) could encode not two amino acids (alanine-alanine) (Fig. 33, A) as in the case of a non-overlapping code, but three (if there is one nucleotide in common) (Fig. 33, B) or five (if two nucleotides are common) (see Fig. 33, C). In the last two cases, a mutation of any nucleotide would lead to a violation in the sequence of two, three, etc. amino acids.

However, it has been established that a mutation of one nucleotide always disrupts the inclusion of one amino acid in a polypeptide. This is a significant argument that the code is non-overlapping.

Let us explain this in Figure 34. Bold lines show triplets encoding amino acids in the case of non-overlapping and overlapping code. Experiments have clearly shown that the genetic code is non-overlapping. Without going into details of the experiment, we note that if you replace the third nucleotide in the sequence of nucleotides (see Fig. 34)U (marked with an asterisk) to some other thing:

1. With a non-overlapping code, the protein controlled by this sequence would have a substitution of one (first) amino acid (marked with asterisks).

2. With an overlapping code in option A, a substitution would occur in two (first and second) amino acids (marked with asterisks). Under option B, the replacement would affect three amino acids (marked with asterisks).

However, numerous experiments have shown that when one nucleotide in DNA is disrupted, the disruption in the protein always affects only one amino acid, which is typical for a non-overlapping code.

GZUGZUG GZUGZUG GZUGZUG

GCU GCU GCU UGC GCU GCU GCU UGC GCU GCU GCU

*** *** *** *** *** ***

Alanin - Alanin Ala - Cis - Ley Ala - Ley - Ley - Ala - Ley

A B C

Non-overlapping code Overlapping code

Rice. 34. A diagram explaining the presence of a non-overlapping code in the genome (explanation in the text).

The non-overlap of the genetic code is associated with another property - the reading of information begins from a certain point - the initiation signal. Such an initiation signal in mRNA is the codon encoding methionine AUG.

It should be noted that a person still has a small number of genes that deviate from the general rule and overlap.

e. Compactness.

There is no punctuation between codons. In other words, triplets are not separated from each other, for example, by one meaningless nucleotide. The absence of “punctuation marks” in the genetic code has been proven in experiments.

and. Versatility.

The code is the same for all organisms living on Earth. Direct evidence of the universality of the genetic code was obtained by comparing DNA sequences with corresponding protein sequences. It turned out that all bacterial and eukaryotic genomes use the same sets of code values. There are exceptions, but not many.

The first exceptions to the universality of the genetic code were found in the mitochondria of some animal species. This concerned the terminator codon UGA, which reads the same as the codon UGG, encoding the amino acid tryptophan. Other rarer deviations from universality were also found.

MZ. The genetic code is a system for recording hereditary information in nucleic acid molecules, based on a certain alternation of nucleotide sequences in DNA or RNA that form codons,

corresponding to amino acids in protein.The genetic code has several properties.

07.04.2015 13.10.2015

In the era of nanotechnology and innovation in all spheres of human life, you need to know a lot for self-confidence and communication with people. Technologies of the twenty-first century have come very far, for example, in the field of medicine and genetics. In this article we will try to describe in detail the most important step of humanity in DNA research.

Description of the DNA code

What is this code? The code is degenerate by genetic properties and geneticists are studying it. All living beings on our planet are endowed with this code. Scientifically defined as a method of protein sequencing of amino acids using a chain of nucleotides.
The so-called alphabet consists of four bases, designated A, G, T, C:
A - adenine,
G – guanine,
T – thymine,
C – cytosine.
The code chain is a spiral of the above-described basics sequentially composed; it turns out that each step of the spiral corresponds to a specific letter.
The DNA code is degenerated by proteins that participate in the composition and are made up of chains. In which twenty types of amino acids are involved. The amino acids of the revealing code are called canonical, they are arranged in a certain way in each creature and form protein units.

History of detection

Humanity has been studying proteins and acids for a long time, but the first hypotheses and the establishment of the theory of heredity arose only in the middle of the twentieth century. At this point, scientists have collected a sufficient amount of knowledge on this issue.
In 1953, research showed that the protein of an individual organism has a unique chain of amino acids. It was further concluded that this chain has no restriction in the polypeptide.

The records of various world scientists, which were different, were compared. Therefore, a certain concept was formed: each gene corresponds to a specific polypeptide. At the same time, the name DNA appeared, which was definitely proven not to be a protein.
Researchers Crick and Watson first talked about the matrix explanatory cipher scheme in 1953. In the most recent work of great scientists, the fact was proven that the cipher is a carrier of information.

Subsequently, it remained to understand only the issue of determining and forming protein amino acid chains, bases and properties.

The first scientist to construct the genetic coding hypothesis was the physicist Gamow, who also proposed a certain way to test the matrix.
Genetics have suggested establishing a correspondence between the two side crossbars of the amino acid chain and the resulting diamond-shaped steps. The diamond-shaped steps of the chain are formed using four nucleotides of the genetic code. This match was called the match of diamonds.
In his further research, Gamow proposes the theory of the triplet code. This assumption becomes paramount in the question of the nature of the genetic code. Although physicist Gamow's theory has shortcomings, one of which is the coding of protein structure through the genetic code.
Accordingly, George Gamow became the first scientist who considered the question of genes as the coding of a four-digit system in its translation into a twenty-digit fundamental fact.

Operating principle

One protein is made up of several strings of amino acids. The logic of connecting chains determines the structure and characteristics of the body’s protein, which accordingly helps to identify information about the biological parameters of a living being.

Information from living cells is obtained by two matrix processes:
Transcription, that is, the synthesized process of fusion of RNA and DNA templates.
Translation, that is, the synthesis of a chain of polypeptides on an RNA matrix.
During the translation process, the genetic code is redirected into a logical chain of amino acids.

To identify and implement gene information, at least three chain nucleotides are required, when considering twenty strictly consecutive amino acids. This set of three nucleotides is referred to as a triplet.
Genetic codes are distributed between two categories:
Overlapping – code minor, triangular and sequential.
Non-overlapping – combination code and “no commas”.
Studies have proven that the order of amino acids is chaotic and accordingly individual, based on this, scientists give preference to non-overlapping codes. Subsequently, the “no comma” theory was refuted.
Why do you need to know the DNA code?
Knowledge of the genetic code of a living organism makes it possible to determine the information of molecules in a hereditary and evolutionary sense. A record of heredity is necessary, reveals research on the formation of systemic knowledge in the world of genetics.
The universality of the genetic code is considered the most unique property of a living organism. Based on the data, answers to most medical and genetic questions can be obtained.

Use of knowledge in medicine and genetics

Advances in molecular biology of the twentieth century allowed for great strides in the study of diseases and viruses with various causes. Information about the genetic code is widely used in medicine and genetics.
Identifying the nature of a particular disease or virus overlaps with the study of genetic development. Knowledge and the formation of theories and practices can cure difficult-to-treat or incurable diseases of the modern world and the future.

Development prospects

Since it has been scientifically proven that the genetic code contains information not only about heredity, but also about the life expectancy of the organism, the development of genetics asks the question of immortality and longevity. This prospect is supported by a number of hypotheses of terrestrial immortality, cancer cells, and human stem cells.

In 1985, a researcher at a technical institute, P. Garyaev, discovered, by accident of spectral analysis, an empty space, which was later called a phantom. Phantoms detect dead genetic molecules.
Which further outlined the theory of changes in a living organism over time, which suggests that a person is able to live for more than four hundred years.
The phenomenon is that DNA cells are capable of producing sound vibrations of one hundred hertz. That is, DNA can speak.

Chemical composition and structural organization of the DNA molecule.

Nucleic acid molecules are very long chains consisting of many hundreds and even millions of nucleotides. Any nucleic acid contains only four types of nucleotides. The functions of nucleic acid molecules depend on their structure, the nucleotides they contain, their number in the chain and the sequence of the compound in the molecule.

Each nucleotide consists of three components: a nitrogenous base, a carbohydrate and a phosphoric acid. IN compound each nucleotide DNA includes one of four types of nitrogenous bases (adenine - A, thymine - T, guanine - G or cytosine - C), as well as deoxyribose carbon and a phosphoric acid residue.

Thus, DNA nucleotides differ only in the type of nitrogenous base.
The DNA molecule consists of a huge number of nucleotides connected in a chain in a certain sequence. Each type of DNA molecule has its own number and sequence of nucleotides.

DNA molecules are very long. For example, to write down the sequence of nucleotides in DNA molecules from one human cell (46 chromosomes) in letters would require a book of about 820,000 pages. The alternation of four types of nucleotides can form an infinite number of variants of DNA molecules. These structural features of DNA molecules allow them to store a huge amount of information about all the characteristics of organisms.

In 1953, the American biologist J. Watson and the English physicist F. Crick created a model of the structure of the DNA molecule. Scientists have found that each DNA molecule consists of two chains interconnected and spirally twisted. It looks like a double helix. In each chain, four types of nucleotides alternate in a specific sequence.

Nucleotide DNA composition varies among different types of bacteria, fungi, plants, and animals. But it does not change with age and depends little on environmental changes. Nucleotides are paired, that is, the number of adenine nucleotides in any DNA molecule is equal to the number of thymidine nucleotides (A-T), and the number of cytosine nucleotides is equal to the number of guanine nucleotides (C-G). This is due to the fact that the connection of two chains to each other in a DNA molecule is subject to a certain rule, namely: adenine of one chain is always connected by two hydrogen bonds only with Thymine of the other chain, and guanine - by three hydrogen bonds with cytosine, that is, the nucleotide chains of one molecule DNA is complementary, complementing each other.

Nucleic acid molecules - DNA and RNA - are made up of nucleotides. DNA nucleotides include a nitrogenous base (A, T, G, C), the carbohydrate deoxyribose and a phosphoric acid molecule residue. The DNA molecule is a double helix, consisting of two chains connected by hydrogen bonds according to the principle of complementarity. The function of DNA is to store hereditary information.

Properties and functions of DNA.

DNA is a carrier of genetic information recorded in the form of a sequence of nucleotides using a genetic code. DNA molecules are associated with two fundamental properties of living things organisms - heredity and variability. During a process called DNA replication, two copies of the original strand are formed, which are inherited by daughter cells when they divide, so that the resulting cells are genetically identical to the original.

Genetic information is realized during gene expression in the processes of transcription (synthesis of RNA molecules on a DNA template) and translation (synthesis of proteins on an RNA template).

The sequence of nucleotides “encodes” information about different types of RNA: messenger or template (mRNA), ribosomal (rRNA) and transport (tRNA). All these types of RNA are synthesized from DNA during the process of transcription. Their role in protein biosynthesis (translation process) is different. Messenger RNA contains information about the sequence of amino acids in a protein, ribosomal RNA serves as the basis for ribosomes (complex nucleoprotein complexes, the main function of which is the assembly of proteins from individual amino acids based on mRNA), transfer RNAs deliver amino acids to the site of protein assembly - to the active center of the ribosome, " crawling" on mRNA.

Genetic code, its properties.

Genetic code- a method characteristic of all living organisms of encoding the amino acid sequence of proteins using a sequence of nucleotides. PROPERTIES:

Triplety- a meaningful unit of code is a combination of three nucleotides (triplet, or codon).
Continuity- there are no punctuation marks between triplets, that is, the information is read continuously.
Non-overlapping- the same nucleotide cannot simultaneously be part of two or more triplets (not observed for some overlapping genes of viruses, mitochondria and bacteria, which encode several frameshift proteins).
Uniqueness (specificity)- a specific codon corresponds to only one amino acid (however, the UGA codon has Euplotes crassus encodes two amino acids - cysteine and selenocysteine)
Degeneracy (redundancy)- several codons can correspond to the same amino acid.
Versatility- the genetic code works the same in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section “Variations of the standard genetic code” below).
Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical.

5. Autoreproduction of DNA. Replicon and its functioning .

The process of self-reproduction of nucleic acid molecules, accompanied by the inheritance (from cell to cell) of exact copies of genetic information; R. carried out with the participation of a set of specific enzymes (helicase<helicase>controlling the unwinding of the molecule DNA, DNA-polymerase<DNA polymerase> I and III, DNA-ligase<DNA ligase>), proceeds in a semi-conservative manner with the formation of a replication fork<replication fork>; on one of the circuits<leading strand> the synthesis of the complementary chain is continuous, and on the other<lagging strand> occurs due to the formation of Dkazaki fragments<Okazaki fragments>; R. - a high-precision process, the error rate of which does not exceed 10 -9; in eukaryotes R. can occur at several points of one molecule at once DNA; speed R. eukaryotes have about 100, and bacteria have about 1000 nucleotides per second.

6. Levels of eukaryotic genome organization .

In eukaryotic organisms, the mechanism of transcription regulation is much more complex. As a result of cloning and sequencing of eukaryotic genes, specific sequences involved in transcription and translation were discovered.
A eukaryotic cell is characterized by:
1. The presence of introns and exons in the DNA molecule.
2. Maturation of mRNA - excision of introns and stitching of exons.
3. The presence of regulatory elements that regulate transcription, such as: a) promoters - 3 types, each of which is occupied by a specific polymerase. Pol I replicates ribosomal genes, Pol II replicates protein structural genes, Pol III replicates genes encoding small RNAs. The Pol I and Pol II promoter are located in front of the transcription initiation site, the Pol III promoter is within the structural gene; b) modulators - DNA sequences that enhance the level of transcription; c) amplifiers - sequences that enhance the level of transcription and act regardless of their position relative to the coding part of the gene and the state of the starting point of RNA synthesis; d) terminators - specific sequences that stop both translation and transcription.
These sequences differ from prokaryotic sequences in their primary structure and location relative to the start codon, and bacterial RNA polymerase does not “recognize” them. Thus, for the expression of eukaryotic genes in prokaryotic cells, the genes must be under the control of prokaryotic regulatory elements. This circumstance must be taken into account when constructing expression vectors.

7. Chemical and structural composition of chromosomes .

Chemical chromosome composition - DNA - 40%, Histone proteins - 40%. Non-histone - 20% some RNA. Lipids, polysaccharides, metal ions.

The chemical composition of a chromosome is a complex of nucleic acids with proteins, carbohydrates, lipids and metals. The chromosome regulates gene activity and restores it in the event of chemical or radiation damage.

STRUCTURAL????

Chromosomes- nucleoprotein structural elements of the cell nucleus, containing DNA, which contains the hereditary Information of the organism, are capable of self-reproduction, have structural and functional individuality and retain it over a number of generations.

in the mitotic cycle the following features of the structural organization of chromosomes are observed:

There are mitotic and interphase forms of the structural organization of chromosomes, mutually transforming into each other in the mitotic cycle - these are functional and physiological transformations

8. Levels of packaging of hereditary material in eukaryotes .

Structural and functional levels of organization of hereditary material of eukaryotes

Heredity and variability provide:

1) individual (discrete) inheritance and change of individual characteristics;

2) reproduction in individuals of each generation of the entire complex of morphofunctional characteristics of organisms of a particular biological species;

3) redistribution in species with sexual reproduction in the process of reproduction of hereditary inclinations, as a result of which the descendant has a combination of characteristics that is different from their combination in the parents. The patterns of inheritance and variability of traits and their sets follow from the principles of the structural and functional organization of genetic material.

There are three levels of organization of the hereditary material of eukaryotic organisms: gene, chromosomal and genomic (genotype level).

The elementary structure of the gene level is the gene. The transfer of genes from parents to offspring is necessary for the development of certain characteristics. Although several forms of biological variability are known, only a violation of the structure of genes changes the meaning of hereditary information, in accordance with which specific characteristics and properties are formed. Thanks to the presence of the gene level, individual, separate (discrete) and independent inheritance and changes in individual characteristics are possible.

Genes in eukaryotic cells are distributed in groups along chromosomes. These are the structures of the cell nucleus, which are characterized by individuality and the ability to reproduce themselves with the preservation of individual structural features over generations. The presence of chromosomes determines the identification of the chromosomal level of organization of hereditary material. The placement of genes on chromosomes affects the relative inheritance of traits and makes it possible for the function of a gene to be influenced by its immediate genetic environment - neighboring genes. The chromosomal organization of hereditary material serves as a necessary condition for the redistribution of the hereditary inclinations of parents in offspring during sexual reproduction.

Despite the distribution on different chromosomes, the entire set of genes functionally behaves as a whole, forming a single system representing the genomic (genotypic) level of organization of the hereditary material. At this level, there is a wide interaction and mutual influence of hereditary inclinations, localized both in one and in different chromosomes. The result is the mutual correspondence of genetic information of different hereditary inclinations and, consequently, the development of traits balanced in time, place and intensity in the process of ontogenesis. The functional activity of genes, the mode of replication and mutational changes in the hereditary material also depend on the characteristics of the genotype of the organism or cell as a whole. This is evidenced, for example, by the relativity of the property of dominance.

Eu - and heterochromatin.

Some chromosomes appear condensed and intensely colored during cell division. Such differences were called heteropyknosis. The term " heterochromatin" There are euchromatin - the main part of mitotic chromosomes, which undergoes the usual cycle of compaction and decompaction during mitosis, and heterochromatin- regions of chromosomes that are constantly in a compact state.

In most species of eukaryotes, chromosomes contain both ew- and heterochromatic regions, the latter making up a significant part of the genome. Heterochromatin located in pericentromeric, sometimes in peritomeric regions. Heterochromatic regions were discovered in the euchromatic arms of chromosomes. They look like inclusions (intercalations) of heterochromatin into euchromatin. Such heterochromatin called intercalary. Chromatin compaction. Euchromatin and heterochromatin differ in compaction cycles. Euhr. goes through a full cycle of compaction-decompaction from interphase to interphase, hetero. maintains a state of relative compactness. Differential stainability. Different areas of heterochromatin are stained with different dyes, some areas with one, others with several. By using various dyes and using chromosomal rearrangements that break up heterochromatic regions, it has been possible to characterize many small regions in Drosophila where the affinity for the stains is different from neighboring regions.

10. Morphological features of the metaphase chromosome .

The metaphase chromosome consists of two longitudinal strands of deoxyribonucleoprotein - chromatids, connected to each other in the region of the primary constriction - the centromere. A centromere is a specially organized region of a chromosome that is common to both sister chromatids. The centromere divides the chromosome body into two arms. Depending on the location of the primary constriction, the following types of chromosomes are distinguished: equal-armed (metacentric), when the centromere is located in the middle and the arms are approximately equal in length; unequal arms (submetacentric), when the centromere is displaced from the middle of the chromosome, and the arms are of unequal length; rod-shaped (acrocentric), when the centromere is shifted to one end of the chromosome and one arm is very short. There are also point (telocentric) chromosomes; they lack one arm, but they are not present in the human karyotype (chromosome set). Some chromosomes may have secondary constrictions that separate a region called a satellite from the chromosome body.

In any cell and organism, all anatomical, morphological and functional features are determined by the structure of the proteins that comprise them. The hereditary property of the body is the ability to synthesize certain proteins. Amino acids are located in a polypeptide chain, on which biological characteristics depend.
Each cell has its own sequence of nucleotides in the polynucleotide chain of DNA. This is the genetic code of DNA. Through it, information about the synthesis of certain proteins is recorded. This article describes what the genetic code is, its properties and genetic information.

A little history

The idea that there might be a genetic code was formulated by J. Gamow and A. Down in the mid-twentieth century. They described that the nucleotide sequence responsible for the synthesis of a particular amino acid contains at least three units. Later they proved the exact number of three nucleotides (this is a unit of genetic code), which was called a triplet or codon. There are sixty-four nucleotides in total, because the acid molecule where RNA occurs is made up of four different nucleotide residues.

What is genetic code

The method of encoding the sequence of amino acid proteins due to the sequence of nucleotides is characteristic of all living cells and organisms. This is what the genetic code is.
There are four nucleotides in DNA:

adenine - A;
guanine - G;
cytosine - C;
thymine - T.

They are denoted by capital Latin or (in Russian-language literature) Russian letters.
RNA also contains four nucleotides, but one of them is different from DNA:

adenine - A;
guanine - G;
cytosine - C;
uracil - U.

All nucleotides are arranged in chains, with DNA having a double helix and RNA having a single helix.
Proteins are built on twenty amino acids, where they, located in a certain sequence, determine its biological properties.

Properties of the genetic code

Tripletity. A unit of genetic code consists of three letters, it is triplet. This means that the twenty amino acids that exist are encoded by three specific nucleotides called codons or trilpets. There are sixty-four combinations that can be created from four nucleotides. This amount is more than enough to encode twenty amino acids.
Degeneracy. Each amino acid corresponds to more than one codon, with the exception of methionine and tryptophan.
Unambiguity. One codon codes for one amino acid. For example, in a healthy person's gene with information about the beta target of hemoglobin, a triplet of GAG and GAA encodes A in everyone who has sickle cell disease, one nucleotide is changed.
Collinearity. The sequence of amino acids always corresponds to the sequence of nucleotides that the gene contains.
The genetic code is continuous and compact, which means that it has no punctuation marks. That is, starting at a certain codon, continuous reading occurs. For example, AUGGGUGTSUAUAUGUG will be read as: AUG, GUG, TSUU, AAU, GUG. But not AUG, UGG and so on or anything else.
Versatility. It is the same for absolutely all terrestrial organisms, from humans to fish, fungi and bacteria.

Table

Not all available amino acids are included in the table presented. Hydroxyproline, hydroxylysine, phosphoserine, iodine derivatives of tyrosine, cystine and some others are absent, since they are derivatives of other amino acids encoded by m-RNA and formed after modification of proteins as a result of translation.
From the properties of the genetic code it is known that one codon is capable of encoding one amino acid. The exception is the genetic code that performs additional functions and encodes valine and methionine. The mRNA, being at the beginning of the codon, attaches t-RNA, which carries formylmethione. Upon completion of the synthesis, it is cleaved off and takes the formyl residue with it, transforming into a methionine residue. Thus, the above codons are the initiators of the synthesis of the polypeptide chain. If they are not at the beginning, then they are no different from the others.

Genetic information

This concept means a program of properties that is passed down from ancestors. It is embedded in heredity as a genetic code.
The genetic code is realized during protein synthesis:

messenger RNA;
ribosomal rRNA.

Information is transmitted through direct communication (DNA-RNA-protein) and reverse communication (medium-protein-DNA).
Organisms can receive, store, transmit it and use it most effectively.
Passed on by inheritance, information determines the development of a particular organism. But due to interaction with the environment, the reaction of the latter is distorted, due to which evolution and development occur. In this way, new information is introduced into the body.

The calculation of the laws of molecular biology and the discovery of the genetic code illustrated the need to combine genetics with Darwin's theory, on the basis of which a synthetic theory of evolution emerged - non-classical biology.
Darwin's heredity, variation and natural selection are complemented by genetically determined selection. Evolution is realized at the genetic level through random mutations and the inheritance of the most valuable traits that are most adapted to the environment.

Decoding the human code

In the nineties, the Human Genome Project was launched, as a result of which genome fragments containing 99.99% of human genes were discovered in the two thousandths. Fragments that are not involved in protein synthesis and are not encoded remain unknown. Their role remains unknown for now.

Last discovered in 2006, chromosome 1 is the longest in the genome. More than three hundred and fifty diseases, including cancer, appear as a result of disorders and mutations in it.

The role of such studies cannot be overestimated. When they discovered what the genetic code is, it became known according to what patterns development occurs, how the morphological structure, psyche, predisposition to certain diseases, metabolism and defects of individuals are formed.

Thanks to the process of transcription in the cell, information is transferred from DNA to protein: DNA - mRNA - protein. The genetic information contained in DNA and mRNA is contained in the sequence of nucleotides in the molecules. How is information transferred from the “language” of nucleotides to the “language” of amino acids? This translation is carried out using the genetic code. A code, or cipher, is a system of symbols for translating one form of information into another. The genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in messenger RNA. How important exactly the sequence of arrangement of the same elements (four nucleotides in RNA) is for understanding and preserving the meaning of information can be seen in a simple example: by rearranging the letters in the word code, we get a word with a different meaning - doc. What properties does the genetic code have?

1. The code is triplet. RNA consists of 4 nucleotides: A, G, C, U. If we tried to designate one amino acid with one nucleotide, then 16 out of 20 amino acids would remain unencrypted. A two-letter code would encrypt 16 amino acids (from four nucleotides, 16 different combinations can be made, each of which contains two nucleotides). Nature has created a three-letter, or triplet, code. This means that each of the 20 amino acids is encoded by a sequence of three nucleotides, called a triplet or codon. From 4 nucleotides you can create 64 different combinations of 3 nucleotides each (4*4*4=64). This is more than enough to encode 20 amino acids and, it would seem, 44 codons are superfluous. However, it is not.

2. The code is degenerate. This means that each amino acid is encrypted by more than one codon (from two to six). The exceptions are the amino acids methionine and tryptophan, each of which is encoded by only one triplet. (This can be seen in the genetic code table.) The fact that methionine is encoded by a single OUT triplet has a special meaning that will become clear to you later (16).

3. The code is unambiguous. Each codon codes for only one amino acid. In all healthy people, in the gene carrying information about the beta chain of hemoglobin, the triplet GAA or GAG, I in sixth place, encodes glutamic acid. In patients with sickle cell anemia, the second nucleotide in this triplet is replaced by U. As can be seen from the table, the triplets GUA or GUG, which are formed in this case, encode the amino acid valine. You already know what such a replacement leads to from the section on DNA.

4. There are “punctuation marks” between genes. In printed text there is a period at the end of each phrase. Several related phrases make up a paragraph. In the language of genetic information, such a paragraph is an operon and its complementary mRNA. Each gene in the operon encodes one polypeptide chain - a phrase. Since in some cases several different polypeptide chains are sequentially created from the mRNA matrix, they must be separated from each other. For this purpose, there are three special triplets in the genetic code - UAA, UAG, UGA, each of which indicates the termination of the synthesis of one polypeptide chain. Thus, these triplets function as punctuation marks. They are found at the end of every gene. There are no "punctuation marks" inside the gene. Since the genetic code is similar to a language, let us analyze this property using the example of a phrase composed of triplets: once upon a time there was a quiet cat, that cat was dear to me. The meaning of what is written is clear, despite the absence of punctuation marks. If we remove one letter in the first word (one nucleotide in the gene), but also read in triplets of letters, then the result will be nonsense: ilb ylk ott ilb yls erm ilm no otk Violation of the meaning also occurs when one or two nucleotides are lost from a gene.The protein that will be read from such a damaged gene will have nothing in common with the protein that was encoded by the normal gene.

6. The code is universal. The genetic code is the same for all creatures living on Earth. In bacteria and fungi, wheat and cotton, fish and worms, frogs and humans, the same triplets encode the same amino acids.