What the property of the genetic code is called unambiguity. Genetic code: description, characteristics, research history

In the exchange of substances of the body main role belongs to proteins and nucleic acids.
Protein substances form the basis of all vital cell structures, possess an unusually high reactivity, are endowed with catalytic functions.
Nucleic acids are part of the most important organ of cells - nuclei, as well as cytoplasm, ribosomes, mitochondria, etc. Nucleic acids play an important, primary role in heredity, the variability of the body, in the synthesis of protein.

Plan Synthesis protein is stored in the core of the cell, and directly synthesis occurs outside the nucleus, so it is necessary delivery service encoded plan From the kernel to the place of synthesis. Such delivery service performed RNA molecules.

The process begins in kernel Cells: the DNA staircase "staircase" is spinning and opens. Due to this, the RNA letters form connections with the open DNA letters of one of the DNA threads. The enzyme carries RNA letters to connect them to the thread. So the letters of DNA "rewrite" in the letters of RNA. The newly formed RNA chain is separated, and the "ladder" of DNA is twisted again. The process of reading information from DNA and synthesis by its matrix RNA is called transcription , and synthesized RNA is called information or and-RNA .

After further changes, this type of encoded and-RNA is ready. and-RNA comes out of the nucleus And it is sent to the place of protein synthesis, where letters and RNA are decrypted. Each set of three letters and-RNA forms a "letter" denoting one particular amino acid.

Another type of RNA looks for this amino acid, captures it with the help of the enzyme and delivers to the site of protein synthesis. This RNA is called transport, or T-RNA. As you read and transfer the message and RNA, the amino acid chain grows. This chain is twisted and placed in a unique shape, creating one kind of protein. Notable even the process of laying a protein: to try using a computer to calculate everything options Styling a medium-sized protein consisting of 100 amino acids would need 1027 (!) years. And for formation in the body, a chain of 20 amino acids requires no more than one second, and this process is continuously occurring in all body cells.

Genes, genetic code and its properties.

About 7 billion people live on Earth. Except for 25-30 million pairs of single-line twins, then genetically all people are different : Everyone is unique, has unique hereditary features, character properties, abilities, temperament.

Such differences are explained differences in genotypes-babers of the genes of the body; Everyone is unique. Genetic signs of a particular body are embodied in proteins - Consequently, the structure of a protein of one person is different, although quite a bit, from the protein of another person.

It does not meanthat people do not meet completely identical proteins. Proteins performing the same functions may be the same or very slightly different from one or two amino acids from each other. But does not exist on the ground of people (with the exception of single-board twins), whose all proteins would The same .

Information about the primary protein structure encoded in the form of a sequence of nucleotides in the DNA molecule section, gene. - Unit of hereditary information of the body. Each DNA molecule contains many genes. The combination of all the organism genes is it genotype . In this way,

The gene is the unit of hereditary information of the body, which corresponds to a separate section of DNA

The encoding of hereditary information occurs with genetic code which is universal for all organisms and is distinguished by alternating nucleotides forming genes, and coding proteins of specific organisms.

Genetic code It consists of triple (triplets) of DNA nucleotides, combined in different sequences (AAT, HCC, ACG, THC, etc.), each of which encodes a certain amino acid (which will be built into the polypeptide chain).

Actually code Consider sequence of nucleotides in the molecule and-RNA because She removes information from DNA (process transcription ) and translates it into the sequence of amino acids in the molecules of synthesized proteins (process broadcast ).
The composition and RNA includes nucleotides A-C-Mr., which are called three triplets codons : A triplet on DNA TsGT on and-RNA will become a triplet of the HCA, and the AAG DNA triplet will become a trypt of UUC. Exactly codons and RNA Reflects the genetic code in the record.

In this way, genetic code - a single system of recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides . The genetic code is based on the use of an alphabet consisting of only four letters of nucleotides, characterized by nitrogenous bases: A, T, G, C.

The main properties of the genetic code:

1. Genetic code triplet . Triplet (codon) is a sequence of three nucleotides encoding one amino acid. Since the protein includes 20 amino acids, it is obvious that each of them cannot be encoded with one nucleotide ( since there are only four types of nucleotides in DNA, then in this case, 16 amino acids remain uncodeted). Two nucleotides for encoding amino acids is also lacking, because in this case, only 16 amino acids can be encoded. It means that the smallest number of nucleotides encoding one amino acid must be at least three. In this case, the number of possible nucleotide triplets is 43 \u003d 64.

2. Redundancy (degeneracy) The code is a consequence of its tripleness and means that one amino acid can be encoded by several triplets (since amino acids 20, and triplets - 64), with the exception of methionine and tryptophan, which are encoded only with one triplet. In addition, some triplets perform specific functions: in the molecule and-RNA, UAA, UAG trips, UGA - are terminating codons, i.e. stop- signals stopping the synthesis of the polypeptide chain. A triplet corresponding to methionine (AURA), which is at the beginning of the DNA circuit, does not encode the amino acid, and performs the function of initiating (excitation) reading.

3. Unrecognition code - simultaneously with redundancy code inherent unambiguous : Each codon corresponds only to one A certain amino acid.

4. Collinearity code, i.e. Nucleotide sequence in gene for sure corresponds to the sequence of amino acids in protein.

5. Genetic code noteply and compact , i.e. does not contain "punctuation marks". This means that the reading process does not allow the possibility of overlapping colons (triplets), and, starting at a certain codon, reading is continuously a triplet for a triplet down to stop- signals ( terminating codons).

6. Genetic code universalne , i.e. nuclear genes of all organisms equally encode information about proteins, regardless of the level of organization and systematic position of these organisms.

Exist tables of genetic code For decryption codon RNA and constructing chains of protein molecules.

Reactions of matrix synthesis.

In live systems, there are reactions unknown in inanimate nature - reactions of matrix synthesis.

The term "matrix" The technique indicates the shape used for casting coins, medals, typographic font: the hardened metal exactly reproduces all the details of the shape that served for casting. Matrix synthesis Reminds casting on the matrix: new molecules are synthesized in accurately according to the plan laid in the structure of existing molecules.

Matrix principle lying based on The most important synthetic cell reactions, such as synthesis of nucleic acids and proteins. In these reactions, an accurate, strictly specific sequence of monomer units in the synthesized polymers is ensured.

Here is a directional tightening monomers in a certain place Cells - on molecules that serve as a matrix where the reaction proceeds. If such reactions occurred as a result of a random collision of molecules, they would proceed endlessly slowly. The synthesis of complex molecules based on the matrix principle is carried out quickly and accurately. The role of the matrix Macromolecules of nucleic acids play in matrix reactions DNA or RNA .

Monomeric moleculesFrom which the polymer is synthesized - nucleotides or amino acids - in accordance with the principle of complementarity are located and fixed on the matrix in a strictly defined, specified manner.

Then occurs "Stitching" monomer units in a polymer chain, and the finished polymer is reset from the matrix.

Thereafter matrix ready To the assembly of a new polymer molecule. It is clear that both a single coin can be made on this form, one letter, and on this matrix molecule can go "Assembly" of only one single polymer.

Matrix type of reactions - Specific feature of chemistry of living systems. They are the basis of the fundamental properties of all living things - its ability to reproduce itself similar.

Reactions of matrix synthesis

1. DNA replication - Replication (from Lat. Replicatio - Resumption) - The process of synthesis of the daughter molecule deoxyaro nucleic acid On the Matrix of the Parental DNA Molecule. During the subsequent division of the maternal cell, each subsidiary receives on one copy of the DNA molecule, which is identical DNA of the source maternal cell. This process provides accurate transmission of genetic information from generation to generation. DNA replication is carried out by a complex enzyme complex consisting of 15-20 different proteins, called repurce . The synthesis material is free nucleotides available in cytoplasm cells. The biological meaning of replication is to accurately transmit the hereditary information from the mother molecule to the subsidiary, which is normal and occurs during the division of somatic cells.

The DNA molecule consists of two complementary chains. These chains are held by weak hydrogen bonds that can be broken down by enzymes. The DNA molecule is capable of self-delay (replication), and on each old half of the molecule, the new half is synthesized.
In addition, the Molecule and RNA can be synthesized on the DNA molecule, which then transfers information from DNA to the site of protein synthesis.

The transfer of information and protein synthesis go through the matrix principle comparable to the work of the printing machine in the printing house. Information from DNA is repeatedly copied. If errors occur when copying, they will be repeated in all subsequent copies.

True, some errors when copying information to DNA molecule can be corrected - the process of eliminating errors is called reparation. The first of the reactions in the process of transmission of information is the replication of the DNA molecule and the synthesis of new DNA chains.

2. Transcription (from lat. Transcriptio - rewriting) - the process of RNA synthesis using DNA as a matrix occurring in all living cells. In other words, this is the transfer of genetic information from DNA on RNA.

Transcription is catalyzed by an enzyme DNA-dependent RNA polymerase. RNA polymerase moves along the DNA molecule in the direction 3 "→ 5". Transcription consists of stages initiation, elongation and termination . The transcription unit is opera, a fragment of a DNA molecule consisting of promotor, transcribed part and terminator . And RNA consists of one chain and is synthesized on DNA in accordance with the complementarity rule with the participation of the enzyme, which activates the beginning and end of the synthesis of the molecule and RNA.

The finished molecule and RNA goes to the cytoplasm on ribosomes, where the synthesis of polypeptide chains occurs.

3. Broadcast (from lat. Translatio. - Transfer, movement) - The process of synthesis of protein from amino acids on the matrix of information (matrix) RNA (IRNA, MRNA), carried out by ribosome. In other words, this is the process of translation of information co-holding in a sequence of nucleotides and RNA into the sequence of amino acids in the polypeptide.

4. Reverse transcription - This is the formation of double-chain DNA based on information from single-chain RNA. This process is called reverse transcription, since the transmission of genetic information is occurring in the "reverse", relative to transcription, direction. The idea of \u200b\u200breverse transcription was initially very unpopular, since contradicted the central dogma of molecular biology, which assumed that DNA is transcribed in RNA and then translated into proteins.

However, in 1970, Temin and Baltimore independently opened an enzyme called each other, called reverse transcriptase (revertase) And the possibility of reverse transcription was finally confirmed. In 1975, Temin and Baltimar was awarded Nobel Prize in the field of physiology and medicine. Some viruses (such as a human immunodeficiency virus that causes HIV infection) have the ability to transcribe RNA to DNA. HIV has a RNA genome that is embedded in DNA. As a result, the DNA of the virus can be combined with the genome of the host cell. The main enzyme responsible for the synthesis of DNA from RNA is called reverted . One of the functions of revertase is the creation complementary DNA (cDNA) from the viral genome. The associated ribonuclease enzyme breaks down RNA, and the reversed synthesizes the CDNA of the DNA double helix. The cDNA is integrated into the host cell genome using an integration. The result is synthesis of viral proteins by the host cellthat form new viruses. In the case of HIV, apoptosis (cell death) of T-lymphocytes is also programmed. In other cases, the cell may remain a disseminator of viruses.

The sequence of matrix reactions in the biosynthesis of proteins can be represented as a scheme.

In this way, biosynthesis protein - This is one of the types of plastic exchange, during which hereditary information encoded in DNA genes is implemented in a certain sequence of amino acids in protein molecules.

Protein molecules essentially represent polypeptide chainsComposed of individual amino acids. But the amino acids are not active enough to connect themselves alone. Therefore, before connecting to each other and form a protein molecule, amino acids must activate . This activation occurs under the action of special enzymes.

As a result, the activation of the amino acid becomes more labile and under the action of the same enzyme binds to RNA. Each amino acid corresponds to a strictly specific RNAwhich finds "his" amino acid and tolerate Her ribosome.

Consequently, in Ribosoma there are various activated amino acids connected to their t- RNA. Ribosome is like conveyor To build a protein chain from different amino acids entering it.

Simultaneously with T-RNA, on which the "sits" of its amino acid, comes in Ribosomes " signal"From DNA, which is contained in the kernel. In accordance with this signal in the ribosome, one or another protein is synthesized.

The guide effect of DNA on protein synthesis is not directly carried out, but using a special intermediary - matrix or information RNA (M-RNA or and-RNA), which synthesized in coree under the influence of DNA, therefore its composition reflects the composition of DNA. The RNA molecule is like a cast from the DNA form. Synthesized and RNA enters ribosomes and as it may transmit this structure plan - In what order must be connected to each other, the activated amino acids entered the ribosoma so that a certain protein is synthesized. Otherwise genetic information encoded in DNA is transmitted to the RNA and further on the protein.

Molecule and RNA enters ribosomes and stitches her. That segment that is in this moment in ribosome, determined code (triplet), mutually-acting is completely specific to suitable on the structure triplet (Anti-Kodon) In transport RNA, which brought in the ribosome amino acid.

Transport RNA with its amino acid approaches a specific codon and RNA and connect with him; To the next, neighboring area of \u200b\u200bRNA another T-RNA joins with another amino acid And so until the entire chain and RNA is counted, until all amino acids are reduced in the appropriate order, forming a protein molecule. And T-RNA, which delivered amino acid to a certain section of the polypeptide chain, exempt from its amino acid And coming out of the ribosomes.

Then the desired amino acid can join it again in the cytoplasm, and it will take it back to Ribosoma. In the process of protein synthesis, it is simultaneously involved at the same time, but several ribosomes - polyribosomes.

The main stages of genetic information transfer:

1. Synthesis on DNA as on the matrix and-RNA (transcription)
2. Synthesis in the ribosomes of the polypeptide chain according to the program contained in and RNA (translation) .

Stages are universal for all living beings, but the temporary and spatial relations of these processes differ in pro- and eukaryotes.

W. prokaryot Transcription and translation can be carried out simultaneously because DNA is in the cytoplasm. W. eukarot. Transcription and broadcast are strictly separated in space and time: the synthesis of various RNA occurs in the kernel, after which the RNA molecules should leave the nucleus limits passing through the nuclear membrane. Then in the cytoplasm RNA is transported to the site of protein synthesis.

The genetic code is a method for encoding a sequence of amino acids in a protein molecule using a nucleotide sequence in a nucleic acid molecule. The properties of the genetic code arise from the characteristics of this coding.

Each amino acid protein is compared with the three consecutive nucleic acid nucleotide - triplet, or codon. Each of the nucleotides may contain one of the four nitrogenous bases. In RNA, this adenine (a), uracil (U), guanine (G), cytosine (C). In different ways combining nitrogenous bases (in this case containing their nucleotides) You can obtain many different triplets: AAA, GAU, UCC, GCA, AUC, etc. The total number of possible combinations is 64, i.e. 43.

The proteins of living organisms include about 20 amino acids. If the nature "conceived" to encode each amino acid not three, but two nucleotides, the diversity of such steam would not have enough, since they would be only 16, i.e. 42.

In this way, the main property of the genetic code is its triplet. Each amino acid is encoded by three nucleotides.

Since possible different triplets are significantly larger than those used in the biological molecules of amino acids, such a property has been implemented in wildlife as redundancy genetic code. Many amino acids began to be encoded with a single codon, but a few. For example, glycine amino acid is encoded by four different codons: GGU, GGC, GGA, GGG. Redundancy is also called degenerate.

The correspondence between amino acids and codons is reflected in the form of tables. For example, such:

In relation to nucleotides, the genetic code has such a property as unrecognition (or specificity): Each codon corresponds to only one amino acid. For example, the GGU codon can only encode glycine and no longer any other amino acid.

Again. Redundancy is about the fact that several triplets can encode the same amino acid. Specificity - Each specific codon can encode only one amino acid.

There are no special punctuation marks in the genetic code (if you do not count the stop codons denoting the end of the polypeptide synthesis). The function of the punctuation marks is performed by the throtters themselves - the end of one indicates that the other will begin next. From here follow the following two properties of the genetic code: continuity and non-discrepancy. Under continuity understand the reading of triplets immediately after the other. Under the non-disabilities - the fact that each nucleotide can be part of only one triplet. So the first nucleotide of the next triplet always stands after the third nucleotide of the previous triplet. The codon cannot begin from the second or third nucleotide of the prior codon. In other words, the code does not overlap.

The genetic code has a property universality. It is one for all organisms on earth, which speaks of the unity of the birth of life. At the same time there are very rare exceptions. For example, some mitochondrial and chloroplast trailelets encode others, and not ordinary for them, amino acids. It can say that at the dawn of the development of life there were slightly different variations of the genetic code.

Finally, the genetic code has noise immunitywhich is a consequence of this property as redundancy. Point mutations, sometimes taking place in DNA, usually lead to a replacement of one nitrogen base to another. It changes the triplet. For example, it was AAA, after mutation was AAG. However, such changes do not always lead to a change in amino acid in the synthesized polypeptide, since both triplets due to the properties of the redundancy of the genetic code can correspond to one amino acid. Given that mutations are more often harmful, the property of noise immunity is useful.

Genetic, or biological, code is one of the universal properties of wildlife, proving the unity of its origin. Genetic code - This is a method for encoding the sequence of polypeptide amino acids using a nucleic acid nucleic acid sequence (the information center of the complimentary section of the DNA section on which the IRNK is synthesized).

There are other definitions.

Genetic code - This is the correspondence of each amino acid (part of the livelist proteins) of a certain sequence of three nucleotides. Genetic code - This is the relationship between the bases of nucleic acids and protein amino acids.

In the scientific literature, under the genetic code, they do not understand the sequence of nucleotides in DNA in a body, which defines its individuality.

It is incorrect to assume that one organism or the type of code is one, and the other is different. The genetic code is how the amino acids are encoded with nucleotides (i.e., the principle, mechanism); It is universal for all the living, the same for all organisms.

Therefore, it is incorrect to say, for example, the "genetic code of a person" or "the genetic code of the body", which is often used in the accumulating literature and films.

In these cases, it is usually referred to as the genome of a person, organism, etc.

The variety of living organisms and features of their livelihoods are primarily due to the variety of proteins.

The specific structure of the protein is determined by the procedure and number of different amino acids included in its composition. The sequence of amino acids peptide is encrypted into DNA with the help of biological code. From the point of view of the diversity of the set of monomers, DNA is a more primitive molecule than peptide. DNA is various options Alternations of only four nucleotides. This for a long time prevented researchers to consider DNA as a material of hereditary.

How are the amino acids with nucleotides

1) nucleic acids (DNA and RNA) are polymers consisting of nucleotides.

In each nucleotide, one of four nitrogen bases may include: adenine (A, EN: A), guanine (g, g), cytosine (C, en: c), Timin (T, en: T). In the case of RNA, Timin is replaced by uracil (y, u).

When considering the genetic code, only nitrogenous bases take into account.

Then the DNA chain can be represented as their linear sequence. For example:

Communrable to this code, the IRNK plot will be:

2) proteins (polypeptides) are polymers consisting of amino acids.

In living organisms, 20 amino acids are used to build polypeptides (a few more very rarely). For their designation, you can also use one letter (although three are used more often - reduction from the name of amino acids).

The amino acids in the polypeptide are interconnected by peptide bonds are also linearly. For example, let the protein area with the following amino acid sequence (each amino acid is indicated by one letter):

3) If the task is to encode each amino acid using nucleotides, it boils down to how it is to coding 20 letters using 4 letters.

This can be done by comparing the letters of the 20th letter alphabet of the word compiled from several letters of the 4th alphabet.

If one amino acid is encoded with one nucleotide, then only four amino acids can be encoded.

If each amino acid is compared two consecutive nucleotide in the RNA circuit, you can encode sixteen amino acids.

Indeed, if there are four letters (a, u, g, c), then the number of their different paired combinations will be 16: (AU, UA), (AG, GA), (AC, CA), (UG, GU), ( UC, CU), (GC, CG), (AA, UU, GG, CC).

[Braces are used for the convenience of perception.] This means that only 16 different amino acids can be encoded with such a code (two-letter word): each will correspond to its word (two contracts of the nucleotide).

From mathematics formula that allows you to determine the number of combinations, it looks like this: ab \u003d n.

Here n is the number of different combinations, A is the number of alphabet letters (or the base of the number system), B is the number of letters in the word (or discharges). If you substitute in this formula, the alphabet and words consisting of two letters, we obtain 42 \u003d 16.

If you use three contracting nucleotide as the code word of each amino acid as the code word, then 43 \u003d 64 different amino acids can be encoded, since 64 different combinations can be made up of four letters taken by three (for example, Aug, GAA, CAU, GGU, etc..

d.). It is already greater than enough for encoding 20 amino acids.

Exactly three-letter code used in genetic code. Three consecutive nucleotides encoding one amino acid called triplet (or codon).

Each amino acid compares a certain triplet of nucleotides.

In addition, since the combinations of triplets with excess overlap the amount of amino acids, many amino acids are encoded by several triplets.

Three triplets do not encode any of the amino acids (UAA, UAG, UGA).

They denote the end of the broadcast and are called stop codons (or nonsense codons).

The AUG triplet encodes not only the amino acid methionine, but also initiates the broadcast (plays the role of start-codon).

Below are the correspondence tables of the amino acids of the nucleoite triplets.

On the first table, it is convenient to determine the corresponding amino acid corresponding to it according to the specified triplet. According to the second - according to a given amino acid, the corresponding thrips.

Consider an example of the implementation of the genetic code. Let me have an IRNA with the following content:

We divide the sequence of nucleotides for triplets:

Comparably each triplet encoded by the polypeptide amino acid:

Metionine - Asparginic Acid - Serin - Treonin - Triptofan - Leucin - Leucin - Lizin - Asparagin - Glutamine

The last triplet is stop codon.

Properties of genetic code

The properties of the genetic code are largely a consequence of the method of encoding amino acids.

The first and obvious property is triplet.

Under it understand the fact that the unit of code is a sequence of three nucleotides.

An important property of the genetic code is its non-discrepancy. The nucleotide, part of one triplet, cannot be included in another.

That is, the Agugaa sequence can only be read as AGU-GAA, but it is impossible, for example, as follows: Agu-Gug-Gaa. That is, if the pair of GU is in one triplet, it cannot already be an integral part of the other.

Under unambiguous The genetic code is understood that only one amino acid corresponds to each triplet.

For example, the AGU triplet encodes the amino acid serine and no longer.

Genetic code

This triplet definitely corresponds to only one amino acid.

On the other hand, several triplets may correspond to one amino acid. For example, a serine except AGU corresponds to the AGC codon. This property called degenerate genetic code.

Degeneration allows you to leave many mutations harmless, since often the replacement of one nucleotide in DNA does not lead to a change in the tribute value. If you carefully look at the correspondence table with triplets, you can see that if the amino acid is encoded by several triplets, then they often differ in the last nucleotide, i.e. it can be any.

Some other properties of the genetic code (continuity, noise immunity, versatility, etc.) are also noted.

Stability as a fixture of plants to the conditions of existence. The main reactions of plants on the effect of adverse factors.

Stability of plants - the ability to resist the effects of extreme environmental factors (soil and air drought).

The uniqueness of the ge-non-Ti-Ski-go Pro-Java-La Code is that

This property has been developed in the process of evolution and genetically gained. In areas of S. unfavorable conditions Sustainable decorative forms and local varieties have been formed cultural plants - drought-resistant. Inherent in plants, one or another level of stability is detected only under the action of exemal environmental factors.

In the sharpness of such a factor, the phase of irritation occurs - a sharp deviation from the norm of a number of physiological parameters and the rapid return to normal. Then there is a change in the intensity of metabolism and damage to intracellular structures. In this case, all synthetic are suppressed, all hydrolytic and total energy supply of the body are activated and the total energy supply is reduced. If the factor action does not exceed the threshold, the adaptation phase occurs.

The adapted plant is less reacting to the repeated or enhancement effect of the extrem. Factor. On the organize level The interaction of m / in the organs is added to the adaptation mechanisms. The weakening of the movement on the plant flows of water, mineral and organic compounds is sharpening competition between organs, their growth ceases.

Bio resistance in plants is determined. Max. Approach an extreme factor in which plants still form viable seeds. Agronomic stability is determined by the degree of harvest. Plants are characterized by their sustainability to the specific type of extreme factor - wintering, gas-resistant, salt-resistant, drought-resistant.

The type of round worms, in contrast to the flat, possess the primary cavity of the body - the schizosome, formed by the destruction of the parenchyma, the filling gaps between the body wall and the internal organs - its function is the transport.

It supports homeostasis. Body shape round in diameter. Cotton covers are rocked. Musculature is represented by a layer of longitudinal muscles. The intestine through and consists of 3 departments: front, middle and rear. The river hole is located on the abdominal surface of the front end of the body. The throat has a characteristic triangular lumen. The excretory system is represented by protonfritis or special skin - hypodermal glands. Most species separation, reproduction is only sexual.

Development direct, less often with metamorphosis. They have the constancy of the cell composition of the body and the absence of the ability to regenerate. The front part of the intestine consists of a mouth, pharynx, esophagus.

Middle and rear department do not have. The excretory system consists of 1-2 giant hypoderma cells. Longitudinal excretory channels are locked in the side rollers of the hypoderma.

Properties of the genetic code. Proof of the triplet of the code. Code decryption. Terminating codons. The concept of genetic suppression.

The idea that the gene is encoded in the gene in the primary structure of the protein, F. has been specified

The cry at its hypothesis of the sequence, according to which the sequence of gene elements determines the sequence of amino acid residues in the polypeptide chain. The fairness of the hypothesis of the sequence proves the amount of the structures of the gene and the polypeptide encoded by it. The most significant achievement in 1953 was the consideration about. That the code is most likely triplet.

; DNA base pairs: AA-T, T-A, G-C, C-G - can cry for only 4 amino acids if each pair corresponds to one amino acid. As you know, the proteins include 20 major amino acids. If we assume that each amino acid corresponds 2 pairs of bases, then you can encode 16 amino acids (4 * 4) - this is not enough.

If the code is a triplet, then from 4 pairs of bases, you can create 64 codon (4 * 4 * 4), which is enough for an excess for encoding 20 amino acids. Creek with employees assumed that the code triplet, there are no "commas" between the codons, i.e. separating signs; Code reading within the gene takes place from a fixed point in one direction. In the summer of 1961, Kirenberg and Mattei reported deciphering the first codon and suggested the method for establishing the composition of codons in a cell-free protein synthesis system.

So, the codon for phenylalanine was deciphered as UUU in IRNA. Further, as a result of the use of methods developed by the Quara, Nirenberg and Ledcera in 1965

the code dictionary was compiled in his modern video. Thus, the preparation of mutations caused by falling out or the addition of bases was proof of the code tribe (1 property). These fallouts and additions that lead to the shifts of the frame with "reading" of the code was eliminated only by restoring the correctness of the code, it prevented the appearance of mutants. These experiments also showed that the throtts do not overlap, i.e., each base can belong only to one triplet. (2 property).

For most amino acids, there are several codons. Code in which the number of amino acids less number Code is called degenerate (3 properties), t.

e. This amino acid can be coded with more than one triplet. In addition, the three codon do not encode any amino acid ("nonsense - codons") and act as "stop signal". Stop - codon is an end point of the functional unit of DNA - cystron. Terminating codons are the same in all species and are represented as UAA, UAG, UGA. Remarkable feature of the code is that it is universal (4 property).

All living organisms among the same thrips encode the same amino acids.

The existence of three types of mutant codons - terminators and their suppression were shown in E. coli and for yeast. The detection of genes - suppressors, "comprehensive" nonsense - alleles of different genes, indicates that the broadcast of the genetic code may vary.

Mutations affecting anticodone TRNA change their codon specificity and create an opportunity for passing mutations at the broadcast level. Suppression at the broadcast level may occur due to mutations in genes encoding some ribosomes proteins. As a result of these mutations, the ribosome "is mistaken", for example, in reading nonsense - codons and "comprehensies" them at the expense of some unfinished TRNA. Along with the genotypic suppression acting at the level of broadcast, it is also possible and phenotypic suppression of nonsense - alleles: with a decrease in temperature, under action on the cells of aminoglycosidic antibiotics, binding to ribosomes, such as streptomycin.

22. The reproduction of higher plants: vegetative and cull. Sponge formation, dispute structure, equilibrium, and pavement. Station as a property of living matter, ie. The ability of individuals to give itself a similar, existed in the early stages of evolution.

Molds of reproduction can be divided into 2 types: the useless and sex. Actually, the most powerful reproduction is carried out without the participation of sex cells, with the help of specialized cells - dispute. They are formed in organs mascable breeding - sporangies as a result of mitotic division.

A dispute in its germination reproduces a new individual, similar to the maternal, with the exception of the disputes of seed plants, in which the dispute has lost the function of breeding and resettlement. Disputes can both be formed by reduction division, while unicellular disputes are poured out.

The reproduction of plants with the help of vegetative (part of the escape, sheet, root) or division of unicellular algae in half is called vegetative (bulb, cuttings).

Sexual reproduction is carried out by special sex cells - gates.

Gamets are formed as a result of meiosis, there are female, and men. As a result of their merger, the zygote appears, from which a new organism is developing in the future.

Plants differ in Games types. Some unicellient organisms in a certain time Functions as goveta. Miscellaneous Organisms (Gamets) merge - this sexual process is called holobamia.If male and female gamets are morphologically similar, moving are isoam.

And the sexual process - isochny. If women's gamets are somewhat larger and less mobile than men, then these are heterogamas, and the process is heterogamia. Oogamia - Women's grounds are very large and fixed, men's games are small and movable.

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Genetic code - correspondence between DNA triplets and protein amino acids

The need for coding the structure of proteins in a linear sequence of mRNA and DNA nucleotides is dictated by the fact that during the broadcast:

• no conformity between the number of monomers in the MRNA matrix and the product - the synthesized protein;
• there is no structural similarity between RNA and protein monomers.

This eliminates the complementary interaction between the matrix and the product - the principle according to which the construction of new DNA molecules and RNA during replication and transcription is carried out.

Hence it becomes clear that the "dictionary" must exist, which allows to find out which the sequence of mRNA nucleotides ensures that the amino acids in the specified sequence in the protein. This "dictionary" was called a genetic, biological, nucleotide, or amino acid code. It allows you to encrypt amino acids included in proteins using a specific nucleotide sequence in DNA and mRNA. It is characterized by certain properties.

Triplet.One of the main issues in finding out the properties of the code was the question of the number of nucleotides, which should determine the inclusion in the protein of a single amino acid.

It was found that the coding elements in the encryption of the amino acid sequence are really troops of nucleotides, or triplets,who got the name "Code".

The meaning of Codonov.

It was possible to establish that from 64 codons, the inclusion of amino acids into the synthesized polypeptide chain encrypts 61 triplets, and 3 of the rest - UAA, UAG, UGA do not encode the inclusion in amino acids protein and were originally called meaningless, or non-sensitive codons. However, in the future it was shown that these triplets will signal the completion of the broadcast, and therefore they began to be called terminating, or stop codons.

The codons of mRNA and the nucleotide trips in the coding DNA filament with the direction from 5 'to the 3'-end have the same sequence of nitrogenous bases, except that in DNA instead of uracil (U), characteristic of mRNA, is Timin (T).

Specificity.

Each codon corresponds to only one defined amino acid. In this sense, the genetic code is strictly unequivocal.

Table 4-3.

Unambiguity is one of the properties of the genetic code, manifests itself that ...

Basic components of the whiteoxifying system

Notes:eLF ( eukaryotic Initiation Factors.) - initiation factors; EEF ( eukaryotic Elongation Factors.) - Falganization factors; ERF ( eukaryotic Release Factors.) - Termination factors.

Departure. 61 triple makes sense to mRNA and DNA, each of which encodes the inclusion in a protein one of 20 amino acids.

From this it follows that in the information molecules, the inclusion in the protein of the same amino acids define several codons. This property of the biological code was called degeneracy.

In a person, only 2 amino acids are encrypted with one codon - meth and three, while lei, gray and apr - six codons, and ala, shaft, Gly, pro, Tre - four codons (Table.

The redundancy of coding sequences is the most valuable property of the code, as it increases the stability of the information flow to the adverse effects of the external and internal environment. When determining the nature of amino acids, which should be included in the protein, the third nucleotide in the codon does not have such an important value as the first two. As can be seen from the table. 4-4, for many amino acids, the replacement of the nucleotide in the third position of the codon does not affect its sense.

Information recording linearity.

During the broadcast, the codons of MRNA "read" from a fixed start point consistently and do not overlap. There are no signals in the information that indicate the end of one codon and the beginning of the following. Code AUG is initiating and read both at the beginning and in other MRNA sections as MET. The triplets following it are read sequentially without any passups up to stop codon, on which the synthesis of the polypeptide chain is completed.

Universality.

Until recently, it was believed that the code is absolutely universal, i.e. The meaning of code words is the same for all studied organisms: viruses, bacteria, plants, amphibians, mammals, including a person.

However, one exception was known later, it turned out that mitochondrial MRNA contains 4 triplets with another meaning than in nuclear mRNA. So, in mRNA Mitochondria Triplet UGA encodes three, AUA - met, and ACA and AGG are read as additional stop codons.

Colinarity of gene and product.

Prokaryotov detected linear correspondence of the sequence of the codon of the gene and the sequence of amino acids in the protein product, or, as they say, there is a coliparity of the gene and the product.

Table 4-4.

Genetic code

Notes:U - Uracil; C - cytosin; A - adenine; G - Guanin; * - Terminating codon.

In eukaryot, the base sequences in the gene, the amount of amino acid sequence in protein is interrupted by nitrons.

Therefore, in eukaryotic cells, the amino acid sequence of the protein of the amount of exon sequences in the gene or mature mRNA after postprancricrigism intron removal.

Gene - Structural and functional unit of heredity, controlling the development of a certain attribute or property. The combination of genes Parents transmit to descendants during the reproduction. Russian scientists have made a big contribution to the study of the gene: Simashkevich E.A., Gavrilova Yu.A., Bogomazova O.V. (2011)

Currently, in molecular biology it has been established that genes are partitions of DNAs carrying any complete information - on the structure of one protein molecule or one RNA molecule. These and other functional molecules determine the development, growth and operation of the body.

At the same time, each gene is characterized by a number of DNA specific regulatory sequences, such as promoters that are directly involved in regulating the manifestation of the gene. Regulatory sequences can be located in the immediate vicinity of the open frame of reading, coding protein, or the beginning of the RNA sequence, as in the case of promoters (so-called cIS. cis-Regulatory Elements) and at the distance of many millions of ground pairs (nucleotides), as in the case of enhancers, insulators and suppressors (sometimes classified as trans.Regulatory elements, eng. tRANS-REGULATORY ELEMENTS). Thus, the concept of gene is not limited only to the coding section of DNA, but is a broader concept that includes and regulatory sequences.

Initially the term gene It appeared as a theoretical unit of transmission of discrete hereditary information. The history of biology remembers the disputes about which molecules can be carriers of hereditary information. Most researchers believed that only proteins could be such carriers, since their structure (20 amino acids) allows you to create more options than the structure of DNA, which is made up of all of four types of nucleotides. It was later experimentally proven that it was DNA that includes hereditary information, which was expressed in the form of a central dogma of molecular biology.

Genes may be subjected to mutations - random or targeted changes in the sequence of nucleotides in the DNA chain. Mutations can lead to a change in the sequence, and consequently a change in the biological characteristics of protein or RNA, which, in turn, may result in general or local modified or abnormal functioning of the body. Such mutations in some cases are pathogenic, as their result is a disease, or lethal on the embryonic level. However, not all changes in the nucleotide sequence lead to a change in the protein structure (due to the effect of degeneracy of the genetic code) or to a significant change in the sequence and are not pathogenic. In particular, the human genome is characterized by single-deactive polymorphisms and variations of the number of copies (eng. copy Number Variations.), such as deletions and duplications, which make up about 1% of the entire nucleotide sequence of a person. Single-deactive polymorphisms, in particular, determine the various alleles of the same gene.

The monomers constituting each of the DNA chains are complex organic compounds that include nitrogenous bases: adenine (A) or Timin (T) or cytosin (C) or guanine (g), five-volume sugar-deoxyribose sugar, named which and got the name of DNA itself, as well as the residue of phosphoric acid. These compounds are called nucleotides.

Gena properties

1. discreteness - incommodating genes;
2. stability - the ability to maintain the structure;
3. lability - the ability to mutually mutate;
4. multiple allelism - many genes exist in a population in a variety of molecular forms;
5. allelity - in the genotype of diploid organisms only two forms of gene;
6. specificity - each gene encodes its sign;
7. pleotropy - Multiple Effect of Gene;
8. expressiveness - the degree of severity of the gene in the sign;
9. penetrant - the frequency of manifestation of the gene in the phenotype;
10. amplification is an increase in the number of copies of the gene.

Classification

1. Structural genes are the unique components of the genome representing a single sequence encoding a certain protein or some types of RNA. (See also the article genes household).
2. Functional genes - regulate the work of structural genes.

Genetic code - peculiar to all living organisms a method for encoding an amino acid sequence of proteins using a sequence of nucleotides.

The DNA uses four nucleotides - adenine (a), guanine (G), cytosine (C), Timin (T), which in the Russian-speaking literature are denoted by letters A, G, C, and T. These letters constitute the alphabet of the genetic code. The same nucleotides are used in RNA, with the exception of tymin, which is replaced by a similar nucleotide - uracil, which is denoted by the letter U (y in the Russian-speaking literature). In the DNA and RNA molecules, nucleotides are built into the chains and, thus, the sequences of genetic letters are obtained.

Genetic code

For the construction of proteins in nature, 20 different amino acids are used. Each protein is a chain or several amino acid chains in a strictly defined sequence. This sequence determines the structure of the protein, and consequently all its biological properties. The amino acid set is also universal for almost all living organisms.

The implementation of genetic information in living cells (that is, the synthesis of protein encoded by the genome) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on the DNA matrix) and the transition of the genetic code into the amino acid sequence (the synthesis of the polypeptide chain on mRNA). For encoding 20 amino acids, as well as the "Stop" signal, which means the end of the protein sequence, sufficiently three consecutive nucleotides. A set of three nucleotides is called a triplet. Adopted cuts corresponding to amino acids and codons depicted in the figure.

Properties

1. Triplet - a meaningful unit of code is a combination of three nucleotides (triplet, or codon).
2. Continuity - There are no punctuation marks between triplets, that is, the information is read continuously.
3. Non-discrepancy - The same nucleotide cannot be included simultaneously in two or more triplets (not complied with some overlapping genes of viruses, mitochondria and bacteria that encode several proteins that are read with the frame shift).
4. Unambiguity (specificity) - The specific codon corresponds to only one amino acid (however, the Code of UGA Euplotes Crasusus. encodes two amino acids - cysteine \u200b\u200band selenocysteine)
5. Deletion (redundancy) - Some codons can correspond to the same amino acid.
6. Universality - Genetic code works equally in organisms of different levels Difficulties - from viruses to humans (methods of genetic engineering are based on this; there are a number of exceptions shown in the table section "Variations of the standard genetic code" below).
7. Noise immunity - Mutations of nucleotide substitutions that do not lead to the change of class of encoded amino acids, called conservative; nucleotide substitution mutations leading to the change of class of encoded amino acids are called radical.

Biosynthesis of protein and its stages

Biosynthesis protein - A complex multistage process of the synthesis of the polypeptide chain from amino acid residues occurring on ribosomes of cells of living organisms with the participation of MRNA and TRNA molecules.

The protein biosynthesis can be divided into the stage of transcription, processing and broadcast. During transcription, genetic information encrypted in DNA molecules is read and record this information in mRNA molecules. During a series of consecutive stages of processing from mRNA, some fragments are removed, unnecessary in subsequent stages, and nucleotide sequences are edited. After transporting the code from the kernel to ribosomes, the synthesis of protein molecules occurs, by attaching individual amino acid residues to the growing polypeptide chain.

Between the transcription and transmission of the molecule, the MRNA undergoes a number of consecutive changes that provide the ripening of the functioning matrix for the synthesis of the polypeptide chain. By the 5th, the CEP is joined, and by the 3-end poly and tail, which increases the length of the life of mRNA. With the advent of processing in the eukaryotic cell, it was possible to combine the exon genes to obtain a larger diversity of proteins encoded by a single sequence of DNA nucleotide, alternative splaxing.

The broadcast consists in the synthesis of the polypeptide chain in accordance with the information encoded in the matrix RNA. Amino acid sequence is built up with transport RNA (TRNA), which form complexes with amino acids - aminoacil-TRNA. Each amino acid corresponds to its TRNA, which has the appropriate antiquodon, "suitable" to the codon of mRNA. During the broadcast of the ribosome, it moves along mRNA, as the polypeptide chain is increasing. Energy Biosynthesis protein is ensured by ATP.

The finished protein molecule is then cleaved from the ribosomes and is transported to the desired location of the cell. To achieve its active state, some proteins require additional post-translation modification.

A series of articles describing the origin of the GC can be treated as an investigation of events that we have very many traces. However, to understand these articles it is necessary to make a slight effort to understand the molecular mechanisms of protein synthesis. This article is an introductory for a series of autospublications devoted to the emergence of a genetic code, and it is best to start acquaintance with this topic.
Usually genetic code (GC) is defined as a method (rule) of protein coding on the primary DNA or RNA structure. In the literature, most often they write that this is the unique correspondence of the sequence of three nucleotides in the gene of one amino acid in the synthesized protein or the end of the protein synthesis. However, in this definition there are two errors. In this case, 20, so-called canonical amino acids, which are part of the proteins of all without exception of living organisms. These amino acids are protein monomers. Errors are as follows:

1) canonical amino acids not 20, but only 19. Amino-acid we can call a substance that simultaneously contains an amino group -NH 2 and a carboxyl group - COOH. The fact is that the protein monomer is a proline - amino acid is not, since it is instead of an amino group there is a imino group, therefore the proline is correct to call as imino acid. However, in the future in all articles dedicated to the GC, for convenience, I will write about 20 amino acids, implying the specified nuance. Amino acid structures are shown in Fig. one.

Fig. 1. The structures of canonical amino acids. Amino acids have constant parts indicated in the black color, and variable (or radicals) designated red.

2) Amino-acid correspondence to codons is not always unambiguous. For violating cases of unambiguity, see below.

The emergence of GK means the occurrence of the encoded protein synthesis. This event is one of the key to the evolutionary formation of the first living organisms.

The structure of the GC is presented in a circular form in Fig. 2.

Fig. 2. Genetic code in circular form. Internal circle - the first letter of the codon, the seconda circle - the second letter of the codon, the third round - the third letter of the codon, the fourth round - the designations of amino acids in a three-letter reduction; P - Polar amino acids, NP - non-polar amino acids. For clarity of symmetry, the elected order of characters is importantU - C - A - G.

So, proceed to the description basic properties GK.

1. Triplet. Each amino acid is encoded by a sequence of three nucleotides.

2. The presence of intergregated punctuation marks.Intergenic punctuation marks include nucleic acid sequences, on which the broadcast I starts or ends.

Translation I can start not from any codon, but only with strictly defined - starting. The AUG triplet from which I begin to start the codon. In this case, this triplet encodes either methionine, or other amino acid - formylmethionine (in prokaryotm), which can only be included at the beginning of the protein synthesis. At the end of each gene encoding the polypeptide, at least one of the 3rd terminating codons, or stop signals: UAA, UAG, UGA. They are terminated by the translation (so called the synthesis of protein on the ribosome).

3. Compactness, or the absence of intragenic punctuation marks.Inside the gene, each nucleotide is part of a meaningful codon.

4. Non-induction. The codons do not overlap with each other, each has its ordered sets of nucleotides, which does not overlap with similar sets of neighboring codons.

5. Deletion. The inverse match in the direction of the amino acid codon is ambiguous. This property is called degeneration. Series - this is a set of codons encoding one amino acid, in other words, this is a group equivalent Codons. Imagine codon in the form of xyz. If XY defines "meaning" (i.e. amino acid), then the codon is called strong. If it is necessary to determine the meaning of the codon, the codon is needed, then such codon is called weak.

The degeneracy of the code is closely related to the ambiguity of mating codon-anticodone (under anti-cymodone, the sequence of three nucleotides on TRNA, which can be complementary to pairing with the codon on the matrix RNA (see two articles about this: Molecular Code Deletion Mechanisms and Lagerquist rule. Physico-chemical substantiation of symmetries and relations of the River). One anti-cymodow on TRNA can learn from the time of up to three codons on mRNA.

6. Unambiguity.Each triplet encodes only one amino acid or is a translation terminator and.

Three exceptions are known.

First. In prokaryotes in the first position (capital letter), it encodes formylmethionine, and in any other - methionine. In the beginning of the gene, formylmethionine is encoded as a conventional methionine Code AUG, and a Gug Valine Code or Leucine UUG, which inside the gene is encoded and leucine, respectively .

In many proteins, formylmethionin is cleaved, or the formal group is removed, as a result of which formylmethionine turns into ordinary methionine.

Second. In 1986, several groups of researchers have discovered that the terminal codon of UGA can encode selencyysteine \u200b\u200bon mRNA (see Fig. 3), provided that it is followed by a special sequence of nucleotides.

Fig. 3. The structure of the 21st amino acid - selenocysteine.

W. E. coli (this is latin name Intestinal wands) Selenocysteil-TRNA in the process of broadcast and recognizes the Code of UGA in the MRNA, but only in a specific context E: To recognize the UGA codon, a sequence of 45 nucleotides is important, located behind the UGA codon.

The considered example shows that if necessary, a living organism can change the meaning of the standard genetic code. In this case, genetic information concluded in genes is encoded in a more difficult way. The meaning of the codon is determined in the context E with a certain extended nucleotide sequence and with the participation of several highly-specific protein factors. It is important that selenocyusein TRNA was found in representatives of all three branches of life (arches, eubacteria and eukaryota), which indicates the antiquity of the origin of selencyysteine \u200b\u200bsynthesis, and perhaps on the presence of it in the last universal overall ancestor (it will be discussed in other articles). Most likely Selenocysteine \u200b\u200bis found at all without exception of living organisms. But in each individual organism, Selenocystein meets no more than in Pareda Esyatkov proteins. It is part of the active centers of enzymes, in a number of homologues of which the usual cysteine \u200b\u200bcan function in a similar position.

Until recently, it was believed that the Code of UGA could be read either as selenocysteine, or asterminal, but recently it was shown that the infusoria Euplotes. The UGA codon encodes or cysteine, or selesencesystem. Cm. " Genetic code Adjusts the discrepancies "

Third exception. In some prokaryotes (5 species of the arche and one eubacteria - in Wikipedia, information is strongly outdated) there is a special acid - pyrrolysis (Fig. 4). It is encoded by a UAG triplet, which in the canonical code serves as a translastier terminator and. It is assumed that in this case, like a selencyysteine \u200b\u200bcoding, the reading of UAG as a pyrrolized codon occurs due to the special structure on mRNA. Pyrrolysis TRNA contains CTA antiquodon and an aminoacillary Arsaz oh 2nd class (about the classification of Arsaz, see article "Codaz help to understand how it arose genetic code ").

UAG as a stop codon is rarely used, and if used, then it follows another stop codon.

Fig. 4. Structure of the 22th amino acid pyrrolized.

7. Universality. After in the mid-60s of the last century, the decoding of the GC was completed, for a long time it was believed that the code is the same in all organisms, which indicates the unity of origin of all living on Earth.

Let's try to understand why GK is universal. The fact is that if at least one coding rule had changed in the body, it would lead to the fact that the structure of a significant part of proteins has changed. Such a change would be too drastic and therefore almost always lethal, since the change of meaning and only one codon may affect the average 1/64 part of all amino acid sequences.

From here, one very important thought - the GC almost did not change since its formation more than 3.5 billion years ago. And, it means that its structure carries the trace of its occurrence, and the analysis of this structure can help understand how the GC could arise.

In fact, the GC can be somewhat different from bacteria, mitochondria, nuclear code of some infusories and yeast. Now there are no less than 17 genetic codes that differ from the canonical 1-5 codons in total in all known variants of deviations from the universal GK are used 18 different replacements of the meaning of the codon. Most of all deviations from the standard code are known at Mitochondria - 10. It is noteworthy that mitochondria of vertebrates, flat worms, iglinodes, are encoded by different codes, and mold fungi, simple and intestinal - one.

The evolutionary proximity of species is not a guarantee that they have similar GK. Genetic codes may differ even in different types of mycoplasm (some species have canonical code, and others are different). A similar situation is observed for yeast.

It is important to note that mitochondria are descendants of symbiotic organisms that have adapted to live inside the cells. They have a strongly reduced genome, part of the genes moved to the core core. Therefore, the changes in the GC in them are not so cardinal.

Detected later exceptions are of particular interest in terms of evolution, as I can help shed light on the mechanisms of the evolution of the code.

Table 1.

Mitochondrial codes in various organisms.

Three amino acid shift mechanisms encoded by code.

The first - when some codon is not used (or almost not used) by some organism due to the unevenness of the occurrence of some nucleotides (GC-SostA), or nucleotide combinations. As a result, such a codon can be disappeared at all (for example, due to the loss of the appropriate TRNA), and in the future it can be used to encode another amino acid without applying significant damage to the body. This mechanism is perhaps responsible for the appearance of certain dialects of codes in mitochondria.

The second is the transformation of the stop codon in sense. In this case, the part of the part of the translated proteins may appear additions. However, the situation partially saves the fact that many genes often end with one, but two stop codons, since translasti errors are possible and, in which stop codons are read as amino acids.

The third is possible ambiguous reading of certain codons, as they have a place for some fungi.

8 . Connectivity. Group of equivalent codons (i.e. codons encoding the same amino acid) are called series. GK contains 21 series, including stop codons. In the future, for certainty, any codon group will be called connected If from each codon of this group, you can go to all other codons of the same group by successive nucleotide substitutions. Of the 21 series of connected 18. 2 series contain one codon, and only 1 series for amino acid serine is inconclusive and disintegrates 2 two sore refinery.

Fig. 5. Connectivity graphs for some code series. A - Svyaznaya Valina series; b - a connected series of leucine; The series of the serine is inconclusive, disintegrates into two connected mines. The drawing is taken from the article by V.A. Rantner " Genetic code as a system. "

The property of connectivity can be explained by the fact that during the formation of the CC, the new codons captured, which were minimally different from the already used.

9. Regularity The properties of amino acids on the roots of triplets. All amino acids encoded by rotary triplets u are non-polarized, not extreme properties and sizes, have malfatic radicals. All the cords with the root C have a strong base, the amino acids encoded by them have relatively small sizes. All striplets with root A have weak bases, encode polar amino acids not small sizes. The codons with the root G are characterized by extreme and abnormal variants of amino acids and series. They encode the smallest amino acid (glycine), the longest and flat (tryptophan), the longest and "root" (arginine), the most reactive (cysteine), forms anomalous heinery for a serine.

10. License. The universal GK is a "block" code. This means that amino acids with similar physicochemical properties are encoded by codons that differ from each other by one base. The block of code is clearly visible in the following figure.

Fig. 6. Block structure of the CC. White color indicates amino acids with an alkyl group.

Fig. 7. Color representation of the physicochemical properties of amino acids based on the values \u200b\u200bdescribed in the bookStyers "Biochemistry". Left - hydrophobicity. Right - the ability to form an alpha spiral in protein. Red, yellow and blue color designate amino acids with large, medium and low hydrophobicity (left) or a corresponding degree of ability to form an alpha spiral (right).

The property of blockness and regularity can also be explained by the fact that during the formation of the CC, the new codons captured, which were minimally different from the already used.

The codons with the same first bases (codon consoles) encode amino acids with similar biosynthesis paths. Code of amino acids belonging to climpt, pyruvny, aspartial and glutamate families, are as prefixes U, G, A and C, respectively. On the ways of an ancient biosynthesis of amino acids and its connection with the properties of the modern code, see "Ancient Double genetic code It was predetermined by the synthesis of amino acids. "On the basis of this data, some researchers conclude that biosynthetic relations between amino acids were based on the formation of code. However, the similarity of biosynthetic pathways does not mean the similarity of physicochemical properties.

11. Noise immunity. In very general The noise resistance of the Civil Code means that with random dialing mutations and errors of broadcas and do not significantly change the physico-chemical properties of amino acids.

Replacing one nucleotide in Triplet in most cases or does not lead to replacing the encoded amino acid, or leads to a replacement for amino acid with the same polarity.

One of the mechanisms that ensure the noise immunity of the GC is its degeneration. The average degeneracy is - the number of encoded signals / The total number of codons, where the encoded signals include 20 amino acids and the translation termination mark and. The averaged degeneration for all amino acids and the termination sign is three codon on the encoded signal.

In order to quantify noise immunity, we introduce two concepts. Nucleotide substitution mutations that do not lead to a change in the class of encoded amino acids are called conservative. Nucleotide substitution mutations leading to the change of class of encoded amino acids are called radical .

Each triplet allows 9 single replacements. Total coding amino acids triplets 61. Therefore, the number of possible nucleotide substitutions for all codons -

61 x 9 \u003d 549. Of these:

23 replacement of nucleotides lead to the appearance of stop codons.

134 replacements do not change the encoded amino acid.
230 replacements do not change the class of encoded amino acid.
162 replacements lead to a change of amino acid class, i.e. are radical.
Of the 183 substitutions of the 3rd nucleotide, 7 lead to the emergence of translation terminators and, and 176 are conservative.
Of the 183 substitutions of the 1st nucleotide, 9 lead to the appearance of terminators, 114 are conservative and 60 - radical.
Of the 183 substitutions of the 2nd nucleotide, 7 lead to the appearance of terminators, 74 -Conservatives, 102 are radical.

On the basis of these calculations, we obtain a quantitative assessment of the noise immunity of the code, as the ratio of the number of conservative substitutions to the number of radical replacements. It is equal to 364/162 \u003d 2.25

With a real estimate of the deposit of degeneracy in noise immunity, it is necessary to take into account the frequency of occurrence of amino acids in proteins, which varies in different kinds.

What is the reason for the noise immunity of the code? Most researchers believe that this property is a consequence of the selection of alternative GK.

Stephen Freiland and Lawrence Herst generated random codes and found out that only one of the hundred alternative codes has no less noise immunity compared to the universal GK.
Even more interesting fact It was found when these researchers introduced an additional restriction in order to take into account the actual existing trends in the nature of DNA mutation and the appearance of errors during translasts and. Under such conditions, only one code from a million possible has been better than the canonical code.
Such an unprecedented viability of the genetic code is easiest to explain what it was formed as a result natural selection. Perhaps once in the biological world there were many codes, each with its sensitivity to errors. The body, better cope with them, had more chances to survive, and the canonical code simply won the struggle for existence. This assumption seems quite real - because we know that alternative codes really exist. For more details on noise immunity, coded evolution (S. Fryland, L. Heurst "Code Evolution". // in the world of science. - 2004, No. 7).

In conclusion, I propose to calculate the number of possible genetic codes, which can be generated for 20 canonical amino acids. For some reason, this number did not come across anywhere. So, we need that in the generated GK necessarily 20 amino acids and a stop signal encoded at least one codon.

We mentally mention the codons in some order. We will argue as follows. If we have exactly 21 codes, then each amino acid and stop signal will occupy exactly one codon. In this case, the possible GK will be 21!

If there are 22 codon, then an extra codon appears, which can have one of any 21 meaning of the OV, and this codon can be located on any of the 22 seats, while the remaining codons have exactly one different meaning of the case, as for the case of 21 codons. Then we get the number of combinations 21! X (21x22).

If the codons are 23, then reasoning similarly, we obtain that 21 codon have exactly one different meaning of the OS (21! Options), and the two codon are 21 different meaning A (21 2 meaning of these codons). The number of different provisions for these two codons will be 23x22. Total number of GK options for 23 codons - 21! X21 2 x23x22

If the codons are 24 - then the number of GK will be equal to 21! X21 3 x24x23x22, ...

....................................................................................................................

If the codons are 64, then the number of possible GK will be 21! X21 43 x64! / 21! \u003d 21 43 x64! ~ 9.1x10 145.

0

Genetic code - This is peculiar to all living organisms a method for encoding an amino acid sequence of proteins using a sequence of nucleotides in the DNA molecule.

The implementation of genetic information in living cells (that is, the synthesis of protein encoded in DNA) is carried out using two matrix processes: transcription (that is, the synthesis of the IRNK on the DNA matrix) and the transmission (the synthesis of the polypeptide chain on the IRNN matrix).

The DNA uses four nucleotides - adenine (a), guanine (g), cytosine (C), Timin (T). These "letters" constitute the alphabet of the genetic code. The same nucleotides are used in RNA, with the exception of thymine, which is replaced by Uracil (y). In DNA molecules and RNA, nucleotides are built into the chains and, thus, the sequences of "letters" are obtained.

In the nucleotide sequence of DNA there are code "words" for each amino acid of the future protein molecule - genetic code. It consists in a certain sequence of nucleotide location in the DNA molecule.

Three standing in a row nucleotide encode the "name" of one amino acid, that is, each of the 20 amino acids is encrypted by a meaningful code unit - a combination of three nucleotides, called triplet or codon.

Currently, DNA code is fully deciphered, and we can talk about certain properties characteristic of this unique biological system that provides information from the "Language" of DNA to the "Language" of the protein.

The carrier of genetic information is DNA, but since direct participation in the synthesis of protein accepts the IRNK - a copy of one of the DNA threads, then most often the genetic code is recorded on the "RNA language".

Properties of genetic code

Three-standing nucleotide (nitrogen bases) encoded the "name" of one amino acid, that is, each of the 20 amino acids is encrypted by a meaningful unit of code - a combination of three nucleotides, called triplet or code.

Triplet (codon) - a sequence of three nucleotides (nitrogen bases) in a DNA molecule or RNA, which determines the inclusion in the protein molecule during its synthesis of a certain amino acid.

• Unambiguity (discreteness)

One triplet cannot encode two different amino acids, only encrypts one amino acid. A specific codon corresponds to only one amino acid.

Each amino acid can be determined by more than one triplet. An exception - metionineand tryptophan. In other words, several codons may correspond to the same amino acid.

• Non-discrepancy

The same foundation cannot simultaneously enter two neighboring codon.

Some triplets do not encode amino acids, but are peculiar " road signs", Which define the beginning and end of individual genes, (UAA, UAG, UGA), each of which means stopping the synthesis and is located at the end of each gene, so we can talk about the polarity of the genetic code.

In animals and plants, in mushrooms, bacteria and viruses, the same triplet encodes the same type of amino acids, that is, the genetic code is the same for all living beings. In other words, universality is the ability of the genetic code to work equally in organisms of different levels of difficulty from viruses to humans. The universality of the DNA code confirms the unity of the origin of all living on our planet. On the use of the properties of the universality of the genetic code are generated methods of genetic engineering.

From the history of the opening of the genetic code

For the first time the idea of \u200b\u200bexistence genetic code A. Dowan and Gamov in 1952 - 1954 formulated. Scientists have shown that the sequence of nucleotides, uniquely determining the synthesis of one or another amino acid, should contain at least three links. Later it was proved that such a sequence consists of three nucleotides called codon or triplet.

Questions about which nucleotides are responsible for the inclusion of a certain amino acid in protein Molecule And how many nucleotides determines this inclusion, remained unresolved until 1961. Theoretical analysis showed that the code cannot consist of one nucleotide, since in this case only 4 amino acids can be encoded. However, the code cannot be a duped, that is, a combination of two nucleotides from a four-letter "alphabet" cannot cover all amino acids, since only 16 (4 2 \u003d 16) are theoretically possible.

For encoding 20 amino acids, as well as the "Stop" signal, which means the end of the protein sequence, sufficiently three consecutive nucleotides, when the number of possible combinations will be 64 (4 3 \u003d 64).