What is the genetic code: general information. What is a genetic code and what are its properties? The genetic code determines the principle of recording information about

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-language 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 its biological properties. The set of amino acids is also universal for almost all living organisms.

The implementation of genetic information in living cells (that is, the synthesis of a protein encoded by a gene) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on a DNA matrix) and translation of the genetic code into an amino acid sequence (synthesis of a polypeptide chain on an mRNA matrix). 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 of different levels of complexity - from viruses to humans. (genetic engineering methods are based on this)

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. Different types of 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 on 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. Synthesized mRNA can be stored for a long time in the form of informationosomes. Transcription and translation occur in different compartments.
7. Some eukaryotic genes have inconsistent localization (labile genes or transposons).
8. Molecular biology methods have revealed the inhibitory effect of histone proteins on the synthesis of mRNA.
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) repair of 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.

In the body's metabolism leading role belongs to proteins and nucleic acids.
Protein substances form the basis of all vital cell structures, have an unusually high reactivity, and are 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, body variability, and 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 place 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 nucleus 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 inanimate nature occur in living systems - 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 is directional action going on here. pulling monomers to a specific location 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 the subsequent division of the mother cell, each daughter cell receives one copy of a DNA molecule that 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 together by weak hydrogen bonds that can be broken by 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 a matrix principle, comparable to the operation of a printing press in a 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 the Nobel Prize in Physiology or 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 of 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 currently located in the ribosome is determined 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.

All morphological, anatomical and functional features of any living cell and organism as a whole are determined by the structure of specific proteins that make up the cells. The ability to synthesize only strictly defined proteins is a hereditary property of organisms. The sequence of amino acids in the polypeptide chain - the primary structure of the protein, on which its biological properties depend - is determined by the sequence of nucleotides in DNA molecules. The latter is the keeper of hereditary information in cells.

The sequence of nucleotides in the polynucleotide chain of DNA is very specific for each cell and represents genetic code, through which information about the synthesis of certain proteins is recorded. This means that in DNA, each message is encoded with a specific sequence of four characters - A, G, T, C, just as a written message is encoded with characters (letters) of the alphabet or Morse code. The genetic code is triplet, i.e., each amino acid is encoded by a known combination of three adjacent nucleotides, called codon. It is easy to calculate that the number of possible combinations of four nucleotides in threes will be 64.

It turned out that the code is multiple or “degenerate”, i.e. the same amino acid can be encoded by several triplet codons (from 2 to b), while each triplet encodes only one amino acid, for example, in the language of messenger RNA:

• phenylalanine - UUU, UUC;
• isoleucine - AUC, AUC, AUA;
• proline - CCU, CCC, CCA, CCG;
• serine - UCU, UCC, UCA, UCG, AGU, AGC.

Apart from this, the code is non-overlapping, t.s. the same nucleotide cannot simultaneously be part of two neighboring triplets. And finally, this code does not have commas, which means that if one nucleotide is missing, then when reading it, the nearest nucleotide from the neighboring codon will take its place, which will change the entire reading order. Therefore, correct reading of the code from messenger RNA is ensured by telco if it is read from a strictly defined point. The starting codons in the molecule and RNA are the triplets AUG and GU G.

The nucleotide code is universal for all living organisms and viruses: identical triplets code for identical amino acids. This discovery represents a serious step towards a deeper understanding of the essence of living matter, because the universality of the genetic code indicates the unity of origin of all living organisms. To date, triplets have been deciphered for all 20 amino acids that make up natural proteins. Therefore, knowing the order of triplets in a DNA molecule (genetic code), it is possible to establish the order of amino acids in a protein.

A single DNA molecule can encode the amino acid sequence for many proteins. A functional segment of a DNA molecule that carries information about the structure of one polypeptide or RNA molecule is called genome. There are structural genes, which encode information for the synthesis of structural and enzymatic proteins, and genes with information for the synthesis of tRNA, rRNA, etc.

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

A little history

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

What is genetic code

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

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

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

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

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

Properties of the genetic code

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

Table

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

Genetic information

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

• messenger RNA;
• ribosomal rRNA.

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

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

Decoding the human code

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

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

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

Genetic code– a system for recording genetic information in DNA (RNA) in the form of a certain sequence of nucleotides. A certain sequence of nucleotides in DNA and RNA corresponds to a certain sequence of amino acids in the polypeptide chains of proteins. It is customary to write the code using capital letters of the Russian or Latin alphabet. Each nucleotide is designated by the letter with which the name of the nitrogenous base included in its molecule begins: A (A) - adenine, G (G) - guanine, C (C) - cytosine, T (T) - thymine; in RNA instead of thyminuracil - U (U). The nucleotide sequence determines the sequence of incorporation of AK into the synthesized protein.

Properties of the genetic code:

1. Triplety- 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-overlapping- the same nucleotide cannot simultaneously be part of two or more triplets (not observed for some overlapping genes of viruses, mitochondria and bacteria that encode several frameshift proteins).
4. Unambiguity(specificity) - a specific codon corresponds to only one amino acid (however, the UGA codon in Euplotescrassus encodes two amino acids - cysteine ​​and selenocysteine)
5. Degeneracy(redundancy) - several codons can correspond to the same amino acid.
6. Versatility- the genetic code works the same in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section “Variations of the standard genetic code” below).

Biosynthesis conditions

Protein biosynthesis requires genetic information from the DNA molecule; messenger RNA - the carrier of this information from the nucleus to the place of synthesis; ribosomes - organelles where protein synthesis itself occurs; a set of amino acids in the cytoplasm; transfer RNAs that encode amino acids and transfer them to the site of synthesis on ribosomes; ATP is a substance that provides energy for the encoding and biosynthesis process.

Stages

Transcription- the process of biosynthesis of all types of RNA on a DNA matrix, which occurs in the nucleus.

A certain section of the DNA molecule despirals, the hydrogen bonds between the two chains are destroyed under the action of enzymes. On one DNA strand, as on a template, an RNA copy is synthesized from nucleotides according to the complementary principle. Depending on the DNA section, ribosomal, transport, and messenger RNAs are synthesized in this way.

After mRNA synthesis, it leaves the nucleus and is sent to the cytoplasm to the site of protein synthesis on ribosomes.

Broadcast- the process of synthesis of polypeptide chains carried out on ribosomes, where mRNA is an intermediary in transmitting information about the primary structure of the protein.

Protein biosynthesis consists of a series of reactions.

1. Activation and coding of amino acids. tRNA has the shape of a clover leaf, in the central loop of which there is a triplet anticodon, corresponding to the code for a specific amino acid and the codon on the mRNA. Each amino acid is connected to the corresponding tRNA using the energy of ATP. A tRNA-amino acid complex is formed, which enters the ribosomes.

2. Formation of the mRNA-ribosome complex. mRNA in the cytoplasm is connected by ribosomes on the granular ER.

3. Assembly of the polypeptide chain. tRNA with amino acids, according to the principle of anticodon-codon complementarity, combines with mRNA and enters the ribosome. In the peptide center of the ribosome, a peptide bond is formed between two amino acids, and the released tRNA leaves the ribosome. In this case, the mRNA advances one triplet each time, introducing a new tRNA - an amino acid and removing the released tRNA from the ribosome. The entire process is provided by ATP energy. One mRNA can combine with several ribosomes, forming a polysome, where many molecules of one protein are simultaneously synthesized. Synthesis ends when nonsense codons (stop codes) begin on the mRNA. Ribosomes are separated from mRNA, and polypeptide chains are removed from them. Since the entire synthesis process takes place on the granular endoplasmic reticulum, the resulting polypeptide chains enter the ER tubules, where they acquire their final structure and are converted into protein molecules.

All synthesis reactions are catalyzed by special enzymes with the expenditure of ATP energy. The rate of synthesis is very high and depends on the length of the polypeptide. For example, in the ribosome of Escherichia coli, a protein of 300 amino acids is synthesized in approximately 15-20 seconds.