What is the genetic code and what are its properties. What is a genetic code: general information What is meant by a genetic code

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.

GENETIC CODE, a method of recording hereditary information in nucleic acid molecules in the form of a sequence of nucleotides forming these acids. 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 thymine, uracil is U (U). Each is encoded by a combination of three nucleotides – a triplet, or codon. Briefly, the path of transfer of genetic information is summarized in the so-called. The central dogma of molecular biology: DNA ` RNA f protein.

In special cases, information can be transferred from RNA to DNA, but never from proteins to genes.

The implementation of genetic information is carried out in two stages. In the cell nucleus, informational, or matrix, RNA (transcription) is synthesized on DNA. In this case, the DNA nucleotide sequence is “rewritten” (recoded) into the mRNA nucleotide sequence. Then the mRNA passes into the cytoplasm, attaches to the ribosome, and on it, as on a matrix, the polypeptide chain of the protein is synthesized (translation). Amino acids are attached to the chain under construction using transfer RNA in a sequence determined by the order of nucleotides in the mRNA.

From four “letters” you can make 64 different three-letter “words” (codons). Of the 64 codons, 61 encode specific amino acids, and three are responsible for completing the synthesis of the polypeptide chain. Since there are 61 codons per 20 amino acids that make up proteins, some amino acids are coded by more than one codon (so-called code degeneracy). This redundancy increases the reliability of the code and the entire mechanism of protein biosynthesis. Another property of the code is its specificity (unambiguity): one codon encodes only one amino acid.

In addition, the code does not overlap - information is read in one direction sequentially, triplet by triplet. The most amazing property of the code is its universality: it is the same in all living beings - from bacteria to humans (with the exception of the genetic code of mitochondria). Scientists see this as confirmation of the concept that all organisms descend from one common ancestor.

Deciphering the genetic code, i.e. determining the “meaning” of each codon and the rules by which information is read, was carried out in 1961–1965. and is considered one of the most striking achievements of molecular biology.

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 hereditary information in the form of a sequence of nucleotide bases in DNA molecules (in some viruses - RNA), which determines the primary structure (location of amino acid residues) in protein (polypeptide) molecules. The problem of the genetic code was formulated after proving the genetic role of DNA (American microbiologists O. Avery, K. McLeod, M. McCarthy, 1944) and deciphering its structure (J. Watson, F. Crick, 1953), after establishing that genes determine the structure and functions of enzymes (the principle of “one gene - one enzyme” by J. Beadle and E. Tatem, 1941) and that there is a dependence of the spatial structure and activity of a protein on its primary structure (F. Sanger, 1955). The question of how combinations of 4 nucleic acid bases determine the alternation of 20 common amino acid residues in polypeptides was first posed by G. Gamow in 1954.

Based on an experiment in which they studied the interactions of insertions and deletions of a pair of nucleotides in one of the genes of the T4 bacteriophage, F. Crick and other scientists in 1961 determined the general properties of the genetic code: tripletity, i.e., each amino acid residue in the polypeptide chain corresponds to a set of three bases (triplet, or codon) in the DNA of a gene; codons within a gene are read from a fixed point, in one direction and “without commas”, that is, the codons are not separated by any signs from each other; degeneracy, or redundancy - the same amino acid residue can be encoded by several codons (synonymous codons). The authors assumed that the codons do not overlap (each base belongs to only one codon). Direct study of the coding capacity of triplets was continued using a cell-free protein synthesis system under the control of synthetic messenger RNA (mRNA). By 1965, the genetic code was completely deciphered in the works of S. Ochoa, M. Nirenberg and H. G. Korana. Unraveling the secrets of the genetic code was one of the outstanding achievements of biology in the 20th century.

The implementation of the genetic code in a cell occurs during two matrix processes - transcription and translation. The mediator between the gene and the protein is mRNA, which is formed during transcription on one of the DNA strands. In this case, the sequence of DNA bases, which carries information about the primary structure of the protein, is “rewritten” in the form of a sequence of mRNA bases. Then, during translation on ribosomes, the nucleotide sequence of the mRNA is read by transfer RNAs (tRNAs). The latter have an acceptor end, to which an amino acid residue is attached, and an adapter end, or anticodon triplet, which recognizes the corresponding mRNA codon. The interaction of a codon and an anti-codon occurs on the basis of complementary base pairing: Adenine (A) - Uracil (U), Guanine (G) - Cytosine (C); in this case, the base sequence of the mRNA is translated into the amino acid sequence of the synthesized protein. Different organisms use different synonymous codons with different frequencies for the same amino acid. Reading of the mRNA encoding the polypeptide chain begins (initiates) with the AUG codon corresponding to the amino acid methionine. Less commonly, in prokaryotes, the initiation codons are GUG (valine), UUG (leucine), AUU (isoleucine), and in eukaryotes - UUG (leucine), AUA (isoleucine), ACG (threonine), CUG (leucine). This sets the so-called frame, or phase, of reading during translation, that is, then the entire nucleotide sequence of the mRNA is read triplet by triplet of tRNA until any of the three terminator codons, often called stop codons, are encountered on the mRNA: UAA, UAG , UGA (table). Reading of these triplets leads to the completion of the synthesis of the polypeptide chain.

AUG and stop codons appear at the beginning and end of the regions of mRNA encoding polypeptides, respectively.

The genetic code is quasi-universal. This means that there are slight variations in the meaning of some codons between objects, and this applies primarily to terminator codons, which can be significant; for example, in the mitochondria of some eukaryotes and mycoplasmas, UGA encodes tryptophan. In addition, in some mRNAs of bacteria and eukaryotes, UGA encodes an unusual amino acid - selenocysteine, and UAG in one of the archaebacteria - pyrrolysine.

There is a point of view according to which the genetic code arose by chance (the “frozen chance” hypothesis). It's more likely that it evolved. This assumption is supported by the existence of a simpler and, apparently, more ancient version of the code, which is read in mitochondria according to the “two out of three” rule, when the amino acid is determined by only two of the three bases in the triplet.

Lit.: Crick F. N. a. O. General nature of the genetic code for proteins // Nature. 1961. Vol. 192; The genetic code. N.Y., 1966; Ichas M. Biological code. M., 1971; Inge-Vechtomov S.G. How the genetic code is read: rules and exceptions // Modern natural science. M., 2000. T. 8; Ratner V. A. Genetic code as a system // Soros educational journal. 2000. T. 6. No. 3.

S. G. Inge-Vechtomov.

The genetic code is usually understood as a system of signs indicating the sequential arrangement of nucleotide compounds in DNA and RNA, which corresponds to another sign system displaying the sequence of amino acid compounds in a protein molecule.

It is important!

When scientists managed to study the properties of the genetic code, universality was recognized as one of the main ones. Yes, strange as it may sound, everything is united by one, universal, common genetic code. It was formed over a long period of time, and the process ended about 3.5 billion years ago. Consequently, traces of its evolution can be traced in the structure of the code, from its inception to the present day.

When we talk about the sequence of arrangement of elements in the genetic code, we mean that it is far from chaotic, but has a strictly defined order. And this also largely determines the properties of the genetic code. This is equivalent to the arrangement of letters and syllables in words. Once we break the usual order, most of what we read on the pages of books or newspapers will turn into ridiculous gobbledygook.

Basic properties of the genetic code

Usually the code contains some information encrypted in a special way. In order to decipher the code, you need to know the distinctive features.

So, the main properties of the genetic code are:

• triplicity;
• degeneracy or redundancy;
• unambiguity;
• continuity;
• the versatility already mentioned above.

Let's take a closer look at each property.

1. Triplety

This is when three nucleotide compounds form a sequential chain within a molecule (i.e. DNA or RNA). As a result, a triplet compound is created or encodes one of the amino acids, its location in the peptide chain.

Codons (they are also code words!) are distinguished by their sequence of connections and by the type of those nitrogenous compounds (nucleotides) that are part of them.

In genetics, it is customary to distinguish 64 codon types. They can form combinations of four types of nucleotides, 3 in each. This is equivalent to raising the number 4 to the third power. Thus, the formation of 64 nucleotide combinations is possible.

2. Redundancy of the genetic code

This property is observed when several codons are required to encrypt one amino acid, usually in the range of 2-6. And only tryptophan can be encoded using one triplet.

3. Unambiguity

It is included in the properties of the genetic code as an indicator of healthy genetic inheritance. For example, the GAA triplet, which is in sixth place in the chain, can tell doctors about the good state of the blood, about normal hemoglobin. It is he who carries information about hemoglobin, and it is also encoded by it. And if a person has anemia, one of the nucleotides is replaced by another letter of the code - U, which is a signal of the disease.

4. Continuity

When recording this property of the genetic code, it should be remembered that codons, like links in a chain, are located not at a distance, but in direct proximity, one after another in the nucleic acid chain, and this chain is not interrupted - it has no beginning or end.

5. Versatility

We should never forget that everything on Earth is united by a common genetic code. And therefore, in primates and humans, in insects and birds, in a hundred-year-old baobab tree and a blade of grass that has barely emerged from the ground, similar triplets are encoded by similar amino acids.

It is in genes that the basic information about the properties of a particular organism is contained, a kind of program that the organism inherits from those who lived earlier and which exists as a genetic code.