Genetic code and its properties biology. Degeneracy of the genetic code: general information

Gene classification

1) By the nature of interaction in an allelic pair:

Dominant (a gene capable of suppressing the manifestation of a recessive gene allelic to it); - recessive (a gene whose expression is suppressed by its allelic dominant gene).

2)Functional classification:

2) Genetic code- these are certain combinations of nucleotides and the sequence of their location in the DNA molecule. This is a method characteristic of all living organisms of encoding the amino acid sequence of proteins using a sequence of nucleotides.

DNA uses four nucleotides - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian literature are designated by the letters A, G, T and C. These letters make up the alphabet of the genetic code. RNA uses the same nucleotides, with the exception of thymine, which is replaced by a similar nucleotide - uracil, which is designated by the letter U (U in Russian literature). In DNA and RNA molecules, nucleotides are arranged in chains and, thus, sequences of genetic letters are obtained.

Genetic code

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

Implementation genetic information in living cells (that is, the synthesis of the protein encoded by the gene) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on a DNA template) and translation of the genetic code into an amino acid sequence (synthesis of a polypeptide chain on an mRNA template). Three consecutive nucleotides are sufficient to encode 20 amino acids, as well as the stop signal indicating the end of the protein sequence. A set of three nucleotides is called a triplet. Accepted abbreviations corresponding to amino acids and codons are shown in the figure.

Properties of the genetic code

1. Triplety- a meaningful unit of code is a combination of three nucleotides (a triplet, or codon).

2. Continuity- there are no punctuation marks between triplets, that is, the information is read continuously.

3. Discreteness- the same nucleotide cannot be part of two or more triplets at the same time.

4. Specificity- a specific codon corresponds to only one amino acid.

5. Degeneracy (redundancy)- several codons can correspond to the same amino acid.

6. Versatility - genetic code works the same in organisms different levels complexity - from viruses to humans. (the methods are based on this genetic engineering)

3) transcription - the process of RNA synthesis using DNA as a template that occurs in all living cells. In other words, it is the transfer of genetic information from DNA to RNA.

Transcription is catalyzed by the enzyme DNA-dependent RNA polymerase. The process of RNA synthesis proceeds in the direction from the 5" to the 3" end, that is, along the DNA template strand, RNA polymerase moves in the direction 3"->5"

Transcription consists of the stages of initiation, elongation and termination.

Initiation of transcription- a complex process that depends on the DNA sequence near the transcribed sequence (and in eukaryotes also on more distant parts of the genome - enhancers and silencers) and on the presence or absence of various protein factors.

Elongation- further unwinding of DNA and synthesis of RNA along the coding chain continues. it, like DNA synthesis, occurs in the 5-3 direction

Termination- as soon as the polymerase reaches the terminator, it immediately splits off from the DNA, the local DNA-RNA hybrid is destroyed and the newly synthesized RNA is transported from the nucleus to the cytoplasm, and transcription is completed.

Processing- a set of reactions leading to the conversion of primary products of transcription and translation into functioning molecules. Functionally inactive precursor molecules are exposed to P. ribonucleic acids (tRNA, rRNA, mRNA) and many others. proteins.

In the process of synthesis of catabolic enzymes (breaking down substrates), inducible synthesis of enzymes occurs in prokaryotes. This gives the cell the opportunity to adapt to environmental conditions and save energy by stopping the synthesis of the corresponding enzyme if the need for it disappears.
To induce the synthesis of catabolic enzymes, the following conditions are required:

1. The enzyme is synthesized only when the breakdown of the corresponding substrate is necessary for the cell.
2. The concentration of the substrate in the medium must exceed a certain level before the corresponding enzyme can be formed.
The mechanism of regulation of gene expression in Escherichia coli is best studied using the example of the lac operon, which controls the synthesis of three catabolic enzymes that break down lactose. If there is a lot of glucose and little lactose in the cell, the promoter remains inactive, and the repressor protein is located on the operator - transcription of the lac operon is blocked. When the amount of glucose in the environment, and therefore in the cell, decreases, and lactose increases, the following events occur: the amount of cyclic adenosine monophosphate increases, it binds to the CAP protein - this complex activates the promoter to which RNA polymerase binds; at the same time, excess lactose binds to the repressor protein and releases the operator from it - the path is open for RNA polymerase, transcription of the structural genes of the lac operon begins. Lactose acts as an inducer of the synthesis of those enzymes that break it down.

5) Regulation of gene expression in eukaryotes is much more complicated. Various types cells of a multicellular eukaryotic organism synthesize a number of identical proteins and at the same time they differ from each other in a set of proteins specific to cells of a given type. The level of production depends on the cell type, as well as the stage of development of the organism. Regulation of gene expression is carried out at the cellular and organism levels. The genes of eukaryotic cells are divided into two main types: the first determines the universality of cellular functions, the second determines (determines) specialized cellular functions. Gene functions first group appear in all cells. To carry out differentiated functions, specialized cells must express a specific set of genes.
Chromosomes, genes and operons of eukaryotic cells have a number of structural and functional features, which explains the complexity of gene expression.
1. Operons of eukaryotic cells have several genes - regulators, which can be located in different chromosomes.
2. Structural genes that control the synthesis of enzymes of one biochemical process can be concentrated in several operons, located not only in one DNA molecule, but also in several.
3. Complex sequence of a DNA molecule. There are informative and non-informative sections, unique and repeatedly repeated informative nucleotide sequences.
4. Eukaryotic genes consist of exons and introns, and the maturation of mRNA is accompanied by excision of introns from the corresponding primary RNA transcripts (pro-RNA), i.e. splicing.
5. The process of gene transcription depends on the state of chromatin. Local DNA compaction completely blocks RNA synthesis.
6. Transcription in eukaryotic cells is not always associated with translation. The synthesized mRNA can long time stored in the form of informationosomes. Transcription and translation occur in different compartments.
7. Some eukaryotic genes have variable localization (labile genes or transposons).
8. Methods molecular biology revealed the inhibitory effect of histone proteins on mRNA synthesis.
9. During the development and differentiation of organs, gene activity depends on hormones circulating in the body and causing specific reactions in certain cells. In mammals, the action of sex hormones is important.
10. In eukaryotes, at each stage of ontogenesis, 5-10% of genes are expressed, the rest must be blocked.

6) reparation genetic material

Genetic reparation- the process of eliminating genetic damage and restoring the hereditary apparatus, occurring in the cells of living organisms under the influence of special enzymes. The ability of cells to repair genetic damage was first discovered in 1949 by the American geneticist A. Kellner. Repair- a special function of cells, which consists in the ability to correct chemical damage and breaks in DNA molecules damaged during normal DNA biosynthesis in the cell or as a result of exposure to physical or chemical agents. It is carried out by special enzyme systems of the cell. A number of hereditary diseases (eg, xeroderma pigmentosum) are associated with disorders of repair systems.

types of reparations:

Direct repair is the simplest way to eliminate damage in DNA, which usually involves specific enzymes that can quickly (usually in one stage) eliminate the corresponding damage, restoring the original structure of nucleotides. This is the case, for example, with O6-methylguanine DNA methyltransferase, which removes a methyl group from a nitrogenous base onto one of its own cysteine residues.

The genetic code, expressed in codons, is a system for encoding information about the structure of proteins, inherent in all living organisms on the planet. It took a decade to decipher it, but science understood that it existed for almost a century. Universality, specificity, unidirectionality, and especially the degeneracy of the genetic code are important biological significance.

History of discoveries

The problem of coding has always been key in biology. Science has moved rather slowly towards the matrix structure of the genetic code. Since the discovery of the double helical structure of DNA by J. Watson and F. Crick in 1953, the stage of unraveling the very structure of the code began, which prompted faith in the greatness of nature. The linear structure of proteins and the same structure of DNA implied the presence of a genetic code as a correspondence between two texts, but written using different alphabets. And if the alphabet of proteins was known, then the signs of DNA became the subject of study by biologists, physicists and mathematicians.

There is no point in describing all the steps in solving this riddle. A direct experiment that proved and confirmed that there is a clear and consistent correspondence between DNA codons and protein amino acids was carried out in 1964 by C. Janowski and S. Brenner. And then - the period of deciphering the genetic code in vitro (in a test tube) using protein synthesis techniques in cell-free structures.

The fully deciphered code of E. Coli was made public in 1966 at a symposium of biologists in Cold Spring Harbor (USA). Then the redundancy (degeneracy) of the genetic code was discovered. What this means is explained quite simply.

Decoding continues

Obtaining data on deciphering the hereditary code was one of the most significant events of the last century. Today, science continues to in-depth study the mechanisms of molecular encodings and its systemic features and excess of signs, which expresses the degeneracy property of the genetic code. A separate branch of study is the emergence and evolution of the system for coding hereditary material. Evidence of the connection between polynucleotides (DNA) and polypeptides (proteins) gave impetus to the development of molecular biology. And that, in turn, to biotechnology, bioengineering, discoveries in breeding and plant growing.

Dogmas and rules

The main dogma of molecular biology is that information is transferred from DNA to messenger RNA, and then from it to protein. In the opposite direction, transfer is possible from RNA to DNA and from RNA to another RNA.

But the matrix or basis always remains DNA. And all other fundamental features of information transmission are a reflection of this matrix nature of transmission. Namely, transmission through the synthesis of other molecules on the matrix, which will become the structure for the reproduction of hereditary information.

Genetic code

Linear coding of the structure of protein molecules is carried out using complementary codons (triplets) of nucleotides, of which there are only 4 (adeine, guanine, cytosine, thymine (uracil)), which spontaneously leads to the formation of another chain of nucleotides. The same number and chemical complementarity of nucleotides is the main condition for such a synthesis. But when a protein molecule is formed, there is no quality match between the quantity and quality of monomers (DNA nucleotides are protein amino acids). This is the natural hereditary code - a system for recording the sequence of amino acids in a protein in a sequence of nucleotides (codons).

The genetic code has several properties:

Tripletity.
Unambiguity.
Directionality.
Non-overlapping.
Redundancy (degeneracy) of the genetic code.
Versatility.

Let's give brief description, focusing on biological significance.

Triplety, continuity and the presence of stop signals

Each of the 61 amino acids corresponds to one sense triplet (triplet) of nucleotides. Three triplets do not carry amino acid information and are stop codons. Each nucleotide in the chain is part of a triplet and does not exist on its own. At the end and at the beginning of the chain of nucleotides responsible for one protein, there are stop codons. They start or stop translation (the synthesis of a protein molecule).

Specificity, non-overlap and unidirectionality

Each codon (triplet) codes for only one amino acid. Each triplet is independent of its neighbor and does not overlap. One nucleotide can be included in only one triplet in the chain. Protein synthesis always occurs in only one direction, which is regulated by stop codons.

Redundancy of the genetic code

Each triplet of nucleotides codes for one amino acid. There are 64 nucleotides in total, of which 61 encode amino acids (sense codons), and three are nonsense, that is, they do not encode an amino acid (stop codons). The redundancy (degeneracy) of the genetic code lies in the fact that in each triplet substitutions can be made - radical (lead to the replacement of an amino acid) and conservative (do not change the class of the amino acid). It is easy to calculate that if 9 substitutions can be made in a triplet (positions 1, 2 and 3), each nucleotide can be replaced by 4 - 1 = 3 other options, then total possible options nucleotide substitutions will be 61 by 9 = 549.

The degeneracy of the genetic code is manifested in the fact that 549 variants are much more than are needed to encode information about 21 amino acids. Moreover, out of 549 variants, 23 substitutions will lead to the formation of stop codons, 134 + 230 substitutions are conservative, and 162 substitutions are radical.

Rule of degeneracy and exclusion

If two codons have two identical first nucleotides, and the remaining ones are represented by nucleotides of the same class (purine or pyrimidine), then they carry information about the same amino acid. This is the rule of degeneracy or redundancy of the genetic code. Two exceptions are AUA and UGA - the first encodes methionine, although it should be isoleucine, and the second is a stop codon, although it should encode tryptophan.

The meaning of degeneracy and universality

It is these two properties of the genetic code that have the greatest biological significance. All the properties listed above are characteristic of the hereditary information of all forms of living organisms on our planet.

The degeneracy of the genetic code has adaptive significance, like multiple duplication of the code for one amino acid. In addition, this means a decrease in significance (degeneration) of the third nucleotide in the codon. This option minimizes mutational damage in DNA, which will lead to gross violations in the protein structure. This defense mechanism living organisms on the planet.

- one system records of hereditary information in molecules nucleic acids as a sequence of nucleotides. The genetic code is based on the use of an alphabet consisting of only four letters-nucleotides, distinguished by nitrogenous bases: A, T, G, C.

The main properties of the genetic code are as follows:

1. The genetic code is triplet. A triplet (codon) is a sequence of three nucleotides encoding one amino acid. Since proteins contain 20 amino acids, it is obvious that each of them cannot be encoded by one nucleotide (since there are only four types of nucleotides in DNA, in this case 16 amino acids remain unencoded). Two nucleotides are also not enough to encode amino acids, since in this case only 16 amino acids can be encoded. Means, smallest number number of nucleotides encoding one amino acid is equal to three. (In this case, the number of possible nucleotide triplets is 4 3 = 64).

2. Redundancy (degeneracy) of the code is a consequence of its triplet nature and means that one amino acid can be encoded by several triplets (since there are 20 amino acids and 64 triplets). The exceptions are methionine and tryptophan, which are encoded by only one triplet. In addition, some triplets perform specific functions. So, in the mRNA molecule, three of them UAA, UAG, UGA are stop codons, i.e. stop signals that stop the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), located at the beginning of the DNA chain, does not code for an amino acid, but performs the function of initiating (exciting) reading.

3. Along with redundancy, the code is characterized by the property of unambiguity, which means that each codon corresponds to only one specific amino acid.

4. The code is collinear, i.e. the sequence of nucleotides in a gene exactly matches the sequence of amino acids in a protein.

5. The genetic code is non-overlapping and compact, that is, it does not contain “punctuation marks.” This means that the reading process does not allow for the possibility of overlapping columns (triplets), and, starting at a certain codon, reading proceeds continuously, triplet after triplet, until the stop signals (termination codons). For example, in mRNA the following sequence of nitrogenous bases AUGGGUGTSUAUAUGUG will be read only by such triplets: AUG, GUG, TSUU, AAU, GUG, and not AUG, UGG, GGU, GUG, etc. or AUG, GGU, UGC, CUU, etc. etc. or in some other way (for example, codon AUG, punctuation mark G, codon UGC, punctuation mark U, etc.).

6. The genetic code is universal, i.e. the nuclear genes of all organisms encode information about proteins in the same way, regardless of the level of organization and systematic position these organisms.

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

Plan synthesis protein is stored in the cell nucleus, and direct synthesis occurs outside the nucleus, so it is necessary delivery service encoded plan from the nucleus to the site of synthesis. This delivery service is performed by RNA molecules.

The process starts at core cells: part of the DNA “ladder” unwinds and opens. Thanks to this, the RNA letters form bonds with the open DNA letters of one of the DNA strands. The enzyme transfers the RNA letters to join them into a strand. This is how the letters of DNA are “rewritten” into the letters of RNA. The newly formed RNA chain is separated, and the DNA “ladder” twists again. The process of reading information from DNA and synthesizing it using its RNA matrix is called transcription , and the synthesized RNA is called messenger or mRNA .

After further modifications, this type of encoded mRNA is ready. mRNA comes out of the core and goes to the site of protein synthesis, where the letters of the mRNA are deciphered. Each set of three i-RNA letters forms a “letter” that represents one specific amino acid.

Another type of RNA finds this amino acid, captures it with the help of an enzyme, and delivers it to the site of protein synthesis. This RNA is called transfer RNA, or t-RNA. As the mRNA message is read and translated, the chain of amino acids grows. This chain twists and folds into a unique shape, creating one type of protein. Even the protein folding process is remarkable: it takes a computer to calculate everything options folding an average-sized protein consisting of 100 amino acids would take 1027 (!) years. And it takes no more than one second to form a chain of 20 amino acids in the body, and this process occurs continuously in all cells of the body.

Genes, genetic code and its properties.

About 7 billion people live on Earth. Apart from the 25-30 million pairs of identical twins, genetically all people are different : everyone is unique, has unique hereditary characteristics, character traits, abilities, and temperament.

These differences are explained differences in genotypes- sets of genes of the organism; Each one is unique. The genetic characteristics of a particular organism are embodied in proteins - therefore, the structure of the protein of one person differs, although very slightly, from the protein of another person.

It does not mean that no two people have exactly the same proteins. Proteins that perform the same functions may be the same or differ only slightly by one or two amino acids from each other. But does not exist on Earth of people (with the exception of identical twins) who would have all their proteins are the same .

Protein Primary Structure Information encoded as a sequence of nucleotides in a section of a DNA molecule, gene – a unit of hereditary information of an organism. Each DNA molecule contains many genes. The totality of all the genes of an organism constitutes it genotype . Thus,

Gene is a unit of hereditary information of an organism, which corresponds to a separate section of DNA

Coding of hereditary information occurs using genetic code , which is universal for all organisms and differs only in the alternation of nucleotides that form genes and encode proteins of specific organisms.

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

Actually code counts sequence of nucleotides in an mRNA molecule , because it removes information from DNA (process transcriptions ) and translates it into a sequence of amino acids in the molecules of synthesized proteins (the process broadcasts ).
The composition of mRNA includes nucleotides A-C-G-U, the triplets of which are called codons : a triplet on DNA CGT on i-RNA will become a triplet GCA, and a triplet DNA AAG will become a triplet UUC. Exactly mRNA codons the genetic code is reflected in the record.

Thus, genetic code - a unified system for 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-nucleotides, distinguished by nitrogenous bases: A, T, G, C.

Basic properties of the genetic code:

1. Genetic code triplet. A triplet (codon) is a sequence of three nucleotides encoding one amino acid. Since proteins contain 20 amino acids, it is obvious that each of them cannot be encoded by one nucleotide ( Since there are only four types of nucleotides in DNA, in this case 16 amino acids remain uncoded). Two nucleotides are also not enough to encode amino acids, since in this case only 16 amino acids can be encoded. This 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 = 64.

2. Redundancy (degeneracy) The code is a consequence of its triplet nature and means that one amino acid can be encoded by several triplets (since there are 20 amino acids and 64 triplets), with the exception of methionine and tryptophan, which are encoded by only one triplet. In addition, some triplets perform specific functions: in an mRNA molecule, triplets UAA, UAG, UGA are stop codons, i.e. stop-signals that stop the synthesis of the polypeptide chain. The triplet corresponding to methionine (AUG), located at the beginning of the DNA chain, does not code for an amino acid, but performs the function of initiating (exciting) reading.

3. Unambiguity code - at the same time as redundancy, code has the property unambiguity : each codon matches only one a certain amino acid.

4. Collinearity code, i.e. nucleotide sequence in a gene exactly corresponds to the sequence of amino acids in a protein.

5. Genetic code non-overlapping and compact , i.e. does not contain “punctuation marks”. This means that the reading process does not allow the possibility of overlapping columns (triplets), and, starting at a certain codon, reading proceeds continuously, triplet after triplet, until stop-signals ( stop codons).

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

Exist genetic code tables for decryption codons mRNA and construction of chains of protein molecules.

Matrix synthesis reactions.

Reactions unknown in living systems occur in living systems. inanimate nature - matrix synthesis reactions.

The term "matrix" in technology they designate a mold used for casting coins, medals, and typographic fonts: the hardened metal exactly reproduces all the details of the mold used for casting. Matrix synthesis resembles casting on a matrix: new molecules are synthesized in exact accordance with the plan laid down in the structure of existing molecules.

The matrix principle lies at the core the most important synthetic reactions of the cell, such as the synthesis of nucleic acids and proteins. These reactions ensure the exact, strictly specific sequence of monomer units in the synthesized polymers.

There's directional going on here. contraction of monomers into specific place cells - into molecules that serve as a matrix where the reaction takes place. If such reactions occurred as a result of random collisions of molecules, they would proceed infinitely slowly. The synthesis of complex molecules based on the template principle is carried out quickly and accurately. The role of the matrix macromolecules of nucleic acids play in matrix reactions DNA or RNA .

Monomeric molecules from 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 order.

Then it happens "cross-linking" of monomer units into a polymer chain, and the finished polymer is discharged from the matrix.

After that matrix is ready to the assembly of a new polymer molecule. It is clear that just as on a given mold only one coin or one letter can be cast, so on a given matrix molecule only one polymer can be “assembled”.

Matrix reaction type- a specific feature of the chemistry of living systems. They are the basis of the fundamental property of all living things - its ability to reproduce its own kind.

Template synthesis reactions

1. DNA replication - replication (from Latin replicatio - renewal) - the process of synthesis of a daughter molecule of deoxyribonucleic acid on the matrix of the parent DNA molecule. During subsequent division of the mother cell, each daughter cell receives one copy of a DNA molecule, which is identical to the DNA of the original mother cell. This process ensures that genetic information is accurately passed on from generation to generation. DNA replication is carried out by a complex enzyme complex consisting of 15-20 different proteins, called replisome . The material for synthesis is free nucleotides present in the cytoplasm of cells. The biological meaning of replication lies in the accurate transfer of hereditary information from the mother molecule to the daughter molecules, which normally occurs during the division of somatic cells.

A DNA molecule consists of two complementary strands. These chains are held weak hydrogen bonds, capable of breaking under the action of enzymes. The DNA molecule is capable of self-duplication (replication), and on each old half of the molecule a new half is synthesized.
In addition, an mRNA molecule can be synthesized on a DNA molecule, which then transfers the information received from DNA to the site of protein synthesis.

Information transfer and protein synthesis proceed according to the matrix principle, comparable to the work printing press in the printing house. Information from DNA is copied many times. If errors occur during copying, they will be repeated in all subsequent copies.

True, some errors when copying information with a DNA molecule can be corrected - the process of error elimination is called reparation. The first of the reactions in the process of information transfer is the replication of the DNA molecule and the synthesis of new DNA chains.

2. Transcription (from Latin transcriptio - rewriting) - the process of RNA synthesis using DNA as a template, occurring in all living cells. In other words, it is the transfer of genetic information from DNA to RNA.

Transcription is catalyzed by the 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 unit of transcription is an operon, a fragment of a DNA molecule consisting of promoter, transcribed part and terminator . mRNA consists of a single chain and is synthesized on DNA in accordance with the rule of complementarity with the participation of an enzyme that activates the beginning and end of the synthesis of the mRNA molecule.

The finished mRNA molecule enters the cytoplasm onto ribosomes, where the synthesis of polypeptide chains occurs.

3. Broadcast (from lat. translation- transfer, movement) - the process of protein synthesis from amino acids on a matrix of information (messenger) RNA (mRNA, mRNA), carried out by the ribosome. In other words, this is the process of translating the information contained in the sequence of nucleotides of mRNA into the sequence of amino acids in the polypeptide.

4. Reverse transcription is the process of forming double-stranded DNA based on information from single-stranded RNA. This process is called reverse transcription, since the transfer of genetic information occurs in the “reverse” direction relative to transcription. The idea of reverse transcription was initially very unpopular because it contradicted the central dogma of molecular biology, which assumed that DNA is transcribed into RNA and then translated into proteins.

However, in 1970, Temin and Baltimore independently discovered an enzyme called reverse transcriptase (revertase) , and the possibility of reverse transcription was finally confirmed. In 1975, Temin and Baltimore were awarded Nobel Prize in the field of physiology and medicine. Some viruses (such as the human immunodeficiency virus, which causes HIV infection) have the ability to transcribe RNA into DNA. HIV has an RNA genome that is integrated into 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 reversease. One of the functions of reversease is to create complementary DNA (cDNA) from the viral genome. The associated enzyme ribonuclease cleaves RNA, and reversease synthesizes cDNA from the DNA double helix. The cDNA is integrated into the host cell genome by integrase. The result is synthesis of viral proteins by the host cell, which 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 distributor of viruses.

The sequence of matrix reactions during protein biosynthesis can be represented in the form of a diagram.

Thus, protein biosynthesis- this is one of the types plastic exchange, during which hereditary information, encoded in DNA genes, is implemented into a specific sequence of amino acids in protein molecules.

Protein molecules are essentially polypeptide chains made up of individual amino acids. But amino acids are not active enough to combine with each other on their own. Therefore, before they combine with each other and form a protein molecule, amino acids must activate . This activation occurs under the action of special enzymes.

As a result of activation, the amino acid becomes more labile and, under the action of the same enzyme, binds to t- RNA. Each amino acid corresponds to a strictly specific t- RNA, which finds “its” amino acid and transfers it into the ribosome.

Consequently, various activated amino acids combined with their own T- RNA. The ribosome is like conveyor to assemble a protein chain from various amino acids supplied to it.

Simultaneously with t-RNA, on which its own amino acid “sits”, “ signal"from the DNA that is contained in the nucleus. In accordance with this signal, one or another protein is synthesized in the ribosome.

The directing influence of DNA on protein synthesis is not carried out directly, but with the help of a special intermediary - matrix or messenger RNA (m-RNA or mRNA), which synthesized into the nucleus e under the influence of DNA, so its composition reflects the composition of DNA. The RNA molecule is like a cast of the DNA form. The synthesized mRNA enters the ribosome and, as it were, transfers it to this structure plan- in what order must the activated amino acids entering the ribosome be combined with each other in order for a specific protein to be synthesized? Otherwise, genetic information encoded in DNA is transferred to mRNA and then to protein.

The mRNA molecule enters the ribosome and stitches her. That segment of it that is in this moment in the ribosome, defined codon (triplet), interacts in a completely specific manner with those that are structurally similar to it triplet (anticodon) in transfer RNA, which brought the amino acid into the ribosome.

Transfer RNA with its amino acid matches a specific codon of the mRNA and connects with him; to the next, neighboring section of mRNA another tRNA with a different amino acid is added and so on until the entire chain of i-RNA is read, until all the amino acids are reduced in the appropriate order, forming a protein molecule. And tRNA, which delivered the amino acid to a specific part of the polypeptide chain, freed from its amino acid and exits the ribosome.

Then, again in the cytoplasm, the desired amino acid can join it and again transfer it to the ribosome. In the process of protein synthesis, not one, but several ribosomes - polyribosomes - are involved simultaneously.

The main stages of the transfer of genetic information:

1. Synthesis on DNA as a template for mRNA (transcription)
2. Synthesis of a polypeptide chain in ribosomes according to the program contained in mRNA (translation) .

The stages are universal for all living beings, but the temporal and spatial relationships of these processes differ in pro- and eukaryotes.

U prokaryote transcription and translation can occur simultaneously because DNA is located in the cytoplasm. U eukaryotes transcription and translation are strictly separated in space and time: the synthesis of various RNAs occurs in the nucleus, after which the RNA molecules must leave the nucleus by passing through the nuclear membrane. The RNAs are then transported in the cytoplasm to the site of protein synthesis.

In any cell and organism, all anatomical, morphological and functional features are determined by the structure of the proteins that comprise them. Hereditary property The body is able to synthesize certain proteins. Amino acids are located in the 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 the gene healthy person with information about the beta target of hemoglobin, the triplet of GAG and GAA encodes A in everyone with 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 performer additional functions and encoding valine and methionine, the genetic code. 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 environment the latter's reaction 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.