In the body's metabolism the 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, variability of the body, and in protein synthesis.

Synthesis plan protein is stored in the cell nucleus, and direct synthesis occurs outside the nucleus, so it is necessary help to deliver the encoded plan from the core to the synthesis site. like this help rendered by RNA molecules.

The process begins in the cell nucleus: 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.

After further modifications, this type of encoded RNA is complete.

RNA comes out of the nucleus and goes to the site of protein synthesis, where the RNA letters are deciphered. Each set of three RNA letters forms a "word" representing 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. As the RNA 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 process of protein folding is remarkable: using a computer to calculate all the folding possibilities of an average-sized protein consisting of 100 amino acids would take 10 27 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 there are no people on Earth (with the exception of identical twins) who have all the same proteins.

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 .

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 comprises triplets of nucleotides DNA combining in different ways sequences(AAT, GCA, ACG, TGC, etc.), each of which encodes a specific amino acid(which will be integrated into the polypeptide chain).

Amino acids 20, A opportunities for combinations of four nucleotides in groups of three – 64 four nucleotides are enough to encode 20 amino acids

That's why one amino acid can be encoded several triplets.

Some triplets do not encode amino acids at all, but Launches or stops protein biosynthesis.

Actually the 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 ACGU nucleotides, the triplets of which are called codons: the triplet on DNA CGT on mRNA will become a triplet GCA, and the 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 nucleotide sequence. Genetic code based on the use of an alphabet consisting of only four letters-nucleotides, differing in nitrogenous bases: A, T, G, C.

Basic properties of the genetic code :

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. This means that the smallest number of nucleotides encoding one amino acid is three. (In this case, the number of possible nucleotide triplets is 4 3 = 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 the 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. Along with redundancy, the code has the property unambiguity: Each codon corresponds to only one specific amino acid.

4. The code is collinear, those. 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, 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 the stop signals ( stop codons).

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 of these organisms.

Exist genetic code tables for decoding mRNA codons and constructing chains of protein molecules.

Template synthesis reactions.

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

The term "matrix""in technology they denote 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 DNA or RNA play in matrix reactions.

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 one's own kind.

TO matrix synthesis reactions include:

1. DNA replication - the process of self-duplication of a DNA molecule, carried out under the control of enzymes. On each of the DNA strands formed after the rupture of hydrogen bonds, a daughter DNA strand is synthesized with the participation of the enzyme DNA polymerase. 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 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 – synthesis of i-RNA on DNA, the process of removing information from a DNA molecule, synthesized on it by an i-RNA molecule.

I-RNA 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 i-RNA molecule.

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

3. broadcast - protein synthesis using mRNA; the process of translating the information contained in the nucleotide sequence of mRNA into the sequence of amino acids in the polypeptide.

4 .synthesis of RNA or DNA from RNA viruses

The sequence of matrix reactions during protein biosynthesis can be represented as scheme:

non-transcribed strand of DNA		A T G	G G C	T A T
transcribed strand of DNA		T A C	Ts Ts G	A T A
DNA transcription
mRNA codons		A U G	G G C	U A U
mRNA translation
tRNA anticodons		U A C	Ts Ts G	A U A
protein amino acids		methionine	glycine	tyrosine

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 influence of the same enzyme binds to tRNA. Each amino acid corresponds strictly specific tRNA, which finds“its” amino acid and transfers it into the ribosome.

Consequently, various activated amino acids linked to their tRNAs. 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 i-RNA), which synthesized in the nucleus influenced by 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 way 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 fits to a specific mRNA codon and connects with him; to the next neighboring region of mRNA another tRNA is attached to another amino acid 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 it again will transfer it into 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:

synthesis on DNA as an mRNA template (transcription)

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 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 - ribosomes. Only after this comes the next stage - broadcasting.

In prokaryotes, transcription and translation occur simultaneously.

Thus,

the place of synthesis of proteins and all enzymes in the cell are ribosomes - it’s like "factories" protein, like an assembly shop, where all the materials necessary for assembling the polypeptide chain of protein from amino acids are supplied. Nature of the protein synthesized depends on the structure of i-RNA, on the order of arrangement of nucleoids in it, and the structure of i-RNA reflects the structure of DNA, so that ultimately the specific structure of a protein, i.e., the order of arrangement of various amino acids in it, depends on the order of arrangement of nucleoids in DNA , from the structure of DNA.

The stated theory of protein biosynthesis is called matrix theory. Matrix this theory called because that nucleic acids play the role of matrices in which all the information regarding the sequence of amino acid residues in a protein molecule is recorded.

Creation of a matrix theory of protein biosynthesis and decoding of the amino acid code is the largest scientific achievement of the 20th century, the most important step on the way to elucidating the molecular mechanism of heredity.

Thematic assignments

A1. Which statement is false?

1) the genetic code is universal

2) the genetic code is degenerate

3) the genetic code is individual

4) the genetic code is triplet

A2. One triplet of DNA encodes:

1) sequence of amino acids in a protein

2) one sign of an organism

3) one amino acid

4) several amino acids

A3. "Punctuation marks" of the genetic code

1) trigger protein synthesis

2) stop protein synthesis

3) encode certain proteins

4) encode a group of amino acids

A4. If in a frog the amino acid VALINE is encoded by the triplet GUU, then in a dog this amino acid can be encoded by triplets:

1) GUA and GUG

2) UTC and UCA

3) TsUTs and TsUA

4) UAG and UGA

A5. Protein synthesis is completed at the moment

1) codon recognition by anticodon

2) entry of mRNA to ribosomes

3) the appearance of a “punctuation mark” on the ribosome

4) joining of an amino acid to t-RNA

A6. Indicate a pair of cells in which one person contains different genetic information?

1) liver and stomach cells

2) neuron and leukocyte

3) muscle and bone cells

4) tongue cell and egg

A7. Function of mRNA in the process of biosynthesis

1) storage of hereditary information

2) transport of amino acids to ribosomes

3) transfer of information to ribosomes

4) acceleration of the biosynthesis process

A8. The tRNA anticodon consists of UCG nucleotides. Which DNA triplet is complementary to it?

correlate the substances and structures involved in protein synthesis with their functions by placing the necessary letters next to the numbers 1) a section of DNA

3) RNA POLYMERASE

4) Ribosome

5) polysome

7) AMINO ACID

8)DNA triplet

A) TRANSFERS INFORMATION TO RIBOSOMES

B) site of protein synthesis

c) an enzyme that provides mRNA synthesis

d) source of energy for the reaction

e) protein monomer

e) a group of nucleotides encoding one amino acid

g) a gene encoding information about a protein

h) group of ribosomes, site of protein assembly

the vasopressin protein consists of 9 amino acid residues and is encoded by the following nucleotides with nitrate base residues: ...

A-C-A-A-T-A-A-A-A-G-T-T-T-T-A-A-C-A-G-G-A-G-C-A-C- C-A-... determine how many nucleotides and triplets are in DNA and what is the length of the gene encoding the synthesis of vasopressin.

A section of one of the two chains of the DNA molecule contains 360 nucleotides with thymine (T), 120 nucleotides with adenine (A), 450 nucleotides with cytosine (C) and 150

nucleotides with guanine (G). How many nucleotides with thymine, adenine, cytosine and guanine are contained in 2 strands of a DNA molecule? How many amino acids does this section of the DNA molecule code for?

How many nucleotides does the gene (both strands of DNA) contain that encodes a protein consisting of 330 amino acids? What is its length (distance between

nucleotides in DNA is 0.34 nm)? How long will it take to synthesize this protein if the speed of movement of the ribosome along the mRNA is 6 triplets per second?

Task No. 1.

A fragment of an mRNA chain has the nucleotide sequence: CCCCCCGCAGUA. Determine the sequence of nucleotides in DNA, anticodons in tRNA, and the sequence of amino acids in a fragment of a protein molecule using the genetic code table.

Task No. 2. A fragment of a DNA chain has the following nucleotide sequence: TACCCTCTCTTG. Determine the nucleotide sequence of the mRNA, the anticodons of the corresponding tRNAs, and the amino acid sequence of the corresponding fragment of the protein molecule using the genetic code table.

Problem No. 3
The nucleotide sequence of the DNA chain fragment is AATGCAGGTCATCA. Determine the sequence of nucleotides in mRNA and amino acids in a polypeptide chain. What will happen in a polypeptide if, as a result of a mutation in a gene fragment, the second triplet of nucleotides is lost? Use the gent.code table
Workshop-solving problems on the topic “Protein biosynthesis” (grade 10)

Problem No. 4
The gene region has the following structure: CGG-AGC-TCA-AAT. Indicate the structure of the corresponding section of the protein, information about which is contained in this gene. How will the removal of the fourth nucleotide from the gene affect the structure of the protein?
Problem No. 5
The protein consists of 158 amino acids. How long is the gene encoding it?
Molecular weight of protein X=50000. Determine the length of the corresponding gene. The molecular weight of one amino acid is on average 100.
Problem No. 6
How many nucleotides does the gene (both strands of DNA) contain in which the 51 amino acid protein insulin is programmed?
Problem No. 7
One of the DNA strands has a molecular weight of 34155. Determine the number of monomers of the protein programmed in this DNA. The average molecular weight of one nucleotide is 345.
Problem No. 8
Under the influence of nitrous acid, cytosine is converted to guanine. How will the structure of the synthesized tobacco mosaic virus protein with the amino acid sequence: serine-glycine-serine-isoleucine-threonine-proline change if all cytosine nucleotides are exposed to acid?
Problem No. 9
What is the molecular weight of a gene (two strands of DNA) if a protein with a molecular weight of 1500 is programmed in one strand? The molecular weight of one amino acid is on average 100.
Problem No. 10
A fragment of a polypeptide chain is given: val-gli-phen-arg. Determine the structure of the corresponding t-RNA, i-RNA, DNA.
Problem No. 11
Given a DNA gene fragment: TCT-TCT-TCA-A... Determine: a) the primary structure of the protein encoded in this region; b) the length of this gene;
c) the primary structure of the protein synthesized after the loss of the 4th nucleotide
in this DNA.
Problem No. 12
How many codons will there be in mRNA, nucleotides and triplets in a DNA gene, and amino acids in a protein if 30 tRNA molecules are given?
Problem No. 13

It is known that all types of RNA are synthesized on a DNA template. The fragment of the DNA molecule on which the region of the central loop of tRNA is synthesized has the following nucleotide sequence: ATAGCTGAACGGACT. Establish the nucleotide sequence of the tRNA region that is synthesized on this fragment and the amino acid that this tRNA will carry during protein biosynthesis if the third triplet corresponds to the tRNA anticodon. Explain your answer. To solve the task, use the genetic code table.

13.Semi-conservative

The synthesis of a new chain occurs intermittently with the formation of fragments 700-800-2000 nucleotide residues long. There is a start and end point for replication. The replicon moves along the DNA molecule and its new sections unwind. Each of the mother chains is a template for the daughter chain, which is synthesized according to the principle of complementarity. As a result of successive connections of nucleotides, the DNA chain is lengthened (elongation stage) with the help of the enzyme DNA ligase. When the required length of the molecule is reached, the synthesis stops - termination. In eukaryotes, thousands of replication forks operate at once. In prokaryotes, initiation occurs at one point in the DNA ring, with two replication forks moving in 2 directions. At the point where they meet, the two-stranded DNA molecules are separated.

14. Genetic code -

DNA uses four nucleotides - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian literature are designated by the letters A, G, C and T. 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.

Transcription

Transcription stages:

3). Termination

Broadcast

Processing

15.

13.Semi-conservative– DNA synthesis begins with the attachment of the helicase enzyme to the origin of replication, which unwinds sections of DNA. DNA binding protein (DBP) is attached to each of the chains, preventing their connection. The unit of replication is the replicon - this is the region between two points at which the synthesis of daughter chains begins. The interaction of enzymes with the origin of replication is called initiation. This point moves along the chain (3'OH → 5'P) and a replication fork is formed.

The synthesis of a new chain occurs intermittently with the formation of fragments 700-800-2000 nucleotide residues long. There is a start and end point for replication. The replicon moves along the DNA molecule and its new sections unwind. Each of the mother chains is a template for the daughter chain, which is synthesized according to the principle of complementarity. As a result of successive connections of nucleotides, the DNA chain is lengthened (elongation stage) with the help of the enzyme DNA ligase.

When the required length of the molecule is reached, the synthesis stops - termination. In eukaryotes, thousands of replication forks operate at once. In prokaryotes, initiation occurs at one point in the DNA ring, with two replication forks moving in 2 directions. At the point where they meet, the two-stranded DNA molecules are separated.

14. Genetic code - 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, C and T.

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.

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.

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

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

Non-overlap - the same nucleotide cannot simultaneously be part of two or more triplets. (Not true for some overlapping genes in viruses, mitochondria, and bacteria that encode multiple frameshift proteins.)

Uniqueness - a certain codon corresponds to only one amino acid. (The property is not universal. The UGA codon in Euplotes crassus encodes two amino acids - cysteine ​​and selenocysteine)

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

Universality - the genetic code works the same in organisms of different levels of complexity - from viruses to humans.

Gene expression is the implementation of information recorded in genes, carried out in two stages: transcription, translation.

Transcription- RNA synthesis using DNA as a template. As a result, 3 types of RNA arise: matrix (mRNA), ribosomal (rRNA), transport (tRNA).

Transcription stages:

1). Initiation is the formation of several initial units of RNA.

2). Elongation - further unwinding of DNA and synthesis of RNA along the coding chain continues.

3). Termination- when the polymerase reaches the terminator (transcription starting point), it is immediately cleaved from the DNA, the local DNA-RNA hybrid is destroyed and the newly synthesized RNA is transported from the nucleus to the cytoplasm. Transcription ends.

Broadcast- synthesis of a polypeptide chain using mRNA as a template. All three main types of RNA are involved in translation: m-, p-, tRNA. mRNA is an information matrix; tRNAs “supply” amino acids and recognize mRNA codons; rRNA together with proteins form ribosomes, which hold mRNA, tRNA and protein and carry out the synthesis of the polypeptide chain.

Processing- a set of biochemical reactions in which pre-RNAs are shortened and undergo chemical modifications, as a result of which mature RNAs are formed. A fourth type of RNA, small nuclear RNA (snRNA), is involved in this process.

15. The genomic level of organization of hereditary material, which unites the entire set of chromosomal genes, is an evolutionarily established structure, characterized by relatively greater stability than the gene and chromosomal levels. At the genomic level, a system of genes balanced in doses and united by highly complex functional relationships is something more than a simple collection of individual units. Therefore, the result of the functioning of the genome is the formation of the phenotype of the entire organism. In this regard, the phenotype of an organism cannot be represented as a simple set of characteristics and properties; it is an organism in all the diversity of its characteristics throughout the entire course of individual development. Thus, maintaining the constancy of the organization of hereditary material at the genomic level is of paramount importance to ensure the normal development of the organism and the reproduction of primarily species characteristics in an individual.

At the same time, the admissibility of recombination of units of heredity in the genotypes of individuals determines their genetic diversity, which has important evolutionary significance. Mutational changes that occur at the genomic level of organization of hereditary material - mutations of regulatory genes that have a broad pleiotropic effect, quantitative changes in gene doses, translocations and transpositions of genetic units that affect the nature of gene expression, and finally, the possibility of including foreign information in the genome during horizontal transfer of nucleotides sequences between organisms of different species - sometimes turning out to be evolutionarily promising, are probably the main reason for accelerating the pace of the evolutionary process at certain stages historical development living forms on Earth.

Protein biosynthesis, DNA code, transcription

Each cell synthesizes several thousand different protein molecules. Proteins are short-lived, their existence is limited, after which they are destroyed. The ability to synthesize strictly defined proteins is hereditary; information about the sequence of amino acids in a protein molecule is encoded as a sequence of nucleotides in DNA.

IN genome Humans have less than 100,000 genes, which are located on 23 chromosomes. One chromosome contains several thousand genes, which are arranged in a linear order in certain regions of the chromosome - loci.

A gene is a section of a DNA molecule that encodes the primary sequence of amino acids in a polypeptide or the sequence of nucleotides in transport and ribosomal RNA molecules.

So, a sequence of nucleotides somehow codes for a sequence of amino acids. The entire variety of proteins is formed from 20 different amino acids, and there are 4 types of nucleotides in DNA. If we assume that one nucleotide encodes one amino acid, then 4 nucleotides can encode 4 amino acids; if 2 nucleotides encode one amino acid, then the number of encoded acids increases to 42 - 16. This means that the DNA code must be triplet. It has been proven that exactly three nucleotides encode one amino acid; in this case, 43 - 64 amino acids can be encoded. And since there are only 20 amino acids, some amino acids must be encoded by several triplets.

The following properties of the genetic code are currently known:

1. Triplety: Each amino acid is encoded by a triplet of nucleotides.

2. Unambiguity: A code triplet, a codon, that corresponds to only one amino acid.

3. Degeneracy(redundancy): one amino acid can be encoded by several (up to six) codons.

4. Versatility: the genetic code is the same, the same amino acids are encoded by the same triplets of nucleotides in all organisms on Earth.

5. Non-overlapping: a nucleotide sequence has a reading frame of 3 nucleotides; the same nucleotide cannot be part of two triplets. (Once upon a time there was a quiet cat, that cat was dear to me);

6. Of the 64 code triplets, 61 codons are coding, code for amino acids, and 3 are nonsense, do not code for amino acids, terminating polypeptide synthesis during the work of the ribosome (UAA, UGA, UAG). In addition, there is a codon - initiator(methionine), from which the synthesis of any polypeptide begins.

Table 7.

Genetic code

The first nucleotide in the triplet is one of the four left vertical rows, the second is one of the top horizontal rows, and the third is one of the right vertical rows.

At the beginning of the 50s. F. Crick formulated the central dogma molecular biology:

DNA®RNA®protein.

Information about the protein is located on DNA; mRNA is synthesized on the DNA matrix, which is the matrix for the synthesis of the protein molecule. Template synthesis makes it possible to very accurately and quickly synthesize polymer macromolecules consisting of a huge number of monomers. We encountered matrix synthesis reactions during the doubling of a DNA molecule, the synthesis of mRNA ( transcription) and synthesis of a protein molecule using mRNA ( broadcast) - also matrix synthesis reactions.

Transcription.

Genetic code. Properties of the genetic code.

In accordance with accepted conventions, the beginning of the gene in diagrams is depicted on the left (Fig. 292). The non-coding strand of a DNA molecule has a left end of 5′ and a right end of 3′; the coding, matrix, with which transcription occurs, has the opposite direction. The enzyme responsible for the synthesis of mRNA RNA polymerase, joins promoter, which is located at the 3′ end of the DNA template strand and always moves from the 3′ to the 5′ end. A promoter is a specific sequence of nucleotides to which the enzyme RNA polymerase can attach. It is necessary for mRNA synthesis to begin strictly at the beginning of the gene. From free ribonucleoside triphosphates(ATP, UTP, GTP, CTP), complementary to DNA nucleotides, RNA polymerase forms mRNA.

Rice. 292. Transcription, scheme for the formation of mRNA on a DNA template.

The energy for mRNA synthesis is contained in the high-energy bonds of ribonucleoside triphosphates. The half-life of mRNA is calculated in hours and even days, i.e. they are stable.

Transcription and translation are separated in space and time, transcription occurs in the nucleus and at one time, translation occurs in the cytoplasm and at a completely different time. Transcription requires: 1 - DNA coding strand, matrix; 2 - enzymes, one of them is RNA polymerase; 3 - ribonucleoside triphosphates.

Broadcast

Broadcast- the process of formation of a polypeptide chain on an mRNA matrix, or the conversion of information encoded as a sequence of nucleotides of mRNA into a sequence of amino acids in a polypeptide. The synthesis of protein molecules occurs in the cytoplasm or on the rough endoplasmic reticulum. Proteins for the cell’s own needs are synthesized in the cytoplasm; proteins synthesized in the ER are transported through its channels to the Golgi complex and removed from the cell.

They are used to transport amino acids to ribosomes. transfer RNAs, tRNA. There are more than 30 types of them in a cell, the length of tRNA is from 76 to 85 nucleotide residues, they have tertiary structure due to the pairing of complementary nucleotides and is shaped like a clover leaf. In tRNA there are anticodon loop And acceptor site. At the top of the anticodon loop, each tRNA has anticodon, complementary to the code triplet of a particular amino acid, and the acceptor site at the 3′ end is capable of aminoacyl-tRNA synthetases attach exactly this amino acid (with the consumption of ATP). Thus, each amino acid has their tRNAs And your enzymes, attaching an amino acid to tRNA.

Twenty types of amino acids are encoded by 61 code triplets; theoretically, there can be 61 types of tRNA with corresponding anticodons, that is, one amino acid can have several tRNAs. The existence of several tRNAs capable of binding to the same codon has been established (the last nucleotide in the anticodon is not always important). In total, more than 30 different tRNAs were discovered (Fig. 293).

Organelles responsible for the synthesis of proteins in the cell - ribosomes. In eukaryotes, ribosomes are found in some organelles - mitochondria and plastids (70-S ribosomes) and in the cytoplasm: in free form and on the membranes of the endoplasmic reticulum (80-S ribosomes). The small ribosomal subunit is responsible for genetic, decoding functions; big - for biochemical, enzymatic.

In the small subunit of the ribosome there is a functional center (FC) with two sections - peptidyl(P-plot) and aminoacyl(A-section). The FCR may contain six nucleotides of mRNA, three in the peptidyl and three in the aminoacyl regions.

Protein synthesis begins from the moment when a small ribosomal subunit is attached to the 5′ end of the mRNA, the P site of which enters methionine tRNA with the amino acid methionine (Fig. 294). Any polypeptide chain at the N-terminus first has methionine, which later most often splits off. Polypeptide synthesis proceeds from the N-terminus to the C-terminus, that is, a peptide bond is formed between the carboxyl group of the first and the amino group of the second amino acid.

Then the large ribosomal subunit attaches and a second tRNA enters the A-site, whose anticodon complementarily pairs with the mRNA codon located in the A-site.

Peptidyltransferase center the large subunit catalyzes the formation of a peptide bond between methionine and a second amino acid. There is no separate enzyme that catalyzes the formation of peptide bonds. The energy for the formation of a peptide bond is supplied by the hydrolysis of GTP (Fig. 295).

As soon as a peptide bond is formed, the methionine tRNA is detached from the methionine, and the ribosome moves to the next mRNA code triplet, which ends up in the A site of the ribosome, and the methionine tRNA is pushed into the cytoplasm. 2 GTP molecules are consumed per cycle. Then everything is repeated, a peptide bond is formed between the second and third amino acids.

The broadcast continues until it reaches the A-section stop codon(UAA, UAG or UGA), to which a special protein release factor binds, the protein chain is separated from the tRNA and leaves the ribosome. Dissociation occurs, separation of ribosomal subparticles.

Many proteins are synthesized as precursors containing LP - leader sequence(15 - 25 amino acid residues at the N-terminus, “protein passport”). LPs determine the destination of proteins, the “direction” of the protein (to the nucleus, to the mitochondrion, to the plastids, to the Golgi complex). Proteolytic enzymes then cleave off the drug.

The speed of ribosome movement along mRNA is 5–6 triplets per second; it takes a cell several minutes to synthesize a protein molecule consisting of hundreds of amino acid residues. The first protein synthesized artificially was insulin, consisting of 51 amino acid residues. It took 5,000 operations, involving 10 people over three years.

Thus, translation requires: 1 - mRNA, encoding the sequence of amino acids in the polypeptide; 2 - ribosomes that decode mRNA and form a polypeptide; 3 - tRNAs that transport amino acids to ribosomes; 4 - energy in the form of ATP and GTP for the attachment of amino acids to the ribosome and for the operation of the ribosome; 5 - amino acids, construction material; 6 - enzymes (aminoacyl-tRNA synthetases, etc.).

This article is a repetition of very important information from previously published with some cosmetic improvements: what is the GENETIC CODE. Without a clear understanding of this issue, it is difficult to read some of the other genetics posts, so I HIGHLY advise understanding this topic. It's actually not difficult at all.

So we know that genes somehow contain instructions for making proteins and RNA. With RNA, everything is clear: DNA consists of nucleotides, and RNA consists of them. Therefore, RNA is built very simply: opposite one nucleotide of DNA, one [complementary] nucleotide of the future RNA is attached, and this is how a chain of nucleotides is created that make up RNA - one nucleotide after another. After this, the RNA is detached, undergoes final processing and starts working. Everything is clear here.

What about the construction of proteins? Proteins do not consist of nucleotides, but of amino acid residues. Nucleotides and amino acids are very different from each other; they are simply fundamentally different molecules. And besides, there are only four types of nucleotides in each DNA or RNA molecule, and as many as twenty amino acid residues (and even a little more, as we already know). This means that one nucleotide cannot be assigned to one amino acid. What is needed here is precisely a certain GENETIC CODE, that is, some very specific rules according to which “words” are somehow composed from four “letters”-nucleotides, which must somehow be read and then translated into a sequence of amino acid residues. It looks very difficult, but there can be no other option.

The train of thought of the geneticists who tried to understand this issue was quite simple and predictable - well, at least it seems so now :) Let's go through the chain of their reasoning.

1. DNA, in which our hereditary information is encrypted in the form of genes, consists of a long, very long set of nucleotides, of which there are four types - adenine, guanine, cytosine and thymine (A, G, C, T or, in Russian letters, A, G, C, T). You can try to remember these names all at once; after all, four names is not so much. And if you feel that they are getting confused, well, start memorizing one, for example, choose GUANINE, which owes its euphonious name to guano (sea bird droppings), from which scientists first isolated it. Previously, we had an article about how to easily remember the adenine formula.

2. Proteins are built from amino acid residues, of which there are slightly more than 20 types in terrestrial organisms (more precisely: 20+2+1). We’ll find out later from Elon Musk or Jeff Bezos how things are going for the organisms living on Enceladus :).

3. We know that there is a binary computer code designed in such a way that a certain set of zeros and ones represents a specific number of our decimal system Reckoning. So maybe it's the same pattern here? That is, does a specific sequence of nucleotides designate a specific amino acid?
And if this is so, then there must be some unknown cellular mechanism that somehow understands where to start reading the sequence of nucleotides to build the desired protein? Yes, this must be so, because DNA is incredibly long, you can’t read it all if you only need to find a specific place where the gene begins.

Then there must be cellular mechanisms that will unwind the DNA helix in the right place, otherwise how to read information from the gene?
Then you still need to divide the double helix of DNA in this place into two separate strands and read the information.
And then you will need to stitch the DNA strands back together into one double helix.
And only then it is necessary to somehow transfer the received information to where a certain protein will be created in some incomprehensible way.
It turns out that the cell must have a whole set of molecular mechanisms, served by whole crowds of highly specialized helper proteins?...

So, there is a set of nucleotides. There is a set of amino acids. There must certainly be some kind of logical connection between them. Yes, there are so many “it’s not clear how” here, but there’s simply no other option in sight. Therefore, geneticists followed the precepts of Sherlock Holmes, who discarded impossible versions until one remained, possible, and therefore true. They decided that, most likely, everything is so complicated, and they just need to start carefully studying DNA and looking for answers to all these questions. And their efforts were crowned with success; everything really turned out that way. However, not entirely. Everything turned out to be arranged not just complicated, but extremely complicated, tens of times more complicated than one could initially imagine. And until now we understand all these processes only in the most general terms.

So, knowing that DNA consists of only four types of nucleotides, and proteins are built from twenty amino acids, it is easy to guess that it cannot be that one type of amino acid corresponds to one nucleotide. This means that one DNA “letter” cannot encode one amino acid. How about two? Let’s say if adenine and cytosine (AC) are in a row, then this means one amino acid. Could this be?
We need to count how many combinations we can make from 4 nucleotide letters: AA, AG, AC, AT, GG, GC, GT, CC, CT, TT. All. Ten pieces. Not 20. What if cellular mechanisms are able to distinguish between AG and GA? Will not help. Still only 16 and not 20.
Okay... What if you combine them in groups of three? Well, then there are as many as 64 combinations. Has nature really created such a redundancy of options, why? However, there is no other option, so that’s it?

It turned out that way. One CODON turned out to be exactly three-letter - a group of nucleotides encoding a specific amino acid. And the redundancy of the number of different codons turned out to be a very useful invention of nature (we will write about this later).

So: each amino acid corresponds to at least one combination of three nucleotides located in sequence.
Let's capture this clarity and move on.

For example, if a gene contains a CCC section (cytosine-cytosine-cytosine), then the amino acid proline and no other will be placed in the corresponding place in the protein that is built according to this gene.

After proving the three-letter codon, the question arose: how can as many as 64 possible combinations of three nucleotides code for only 20 amino acids? This time everything turned out to be simple - several codons can indicate the same amino acid.

Remember, we wrote above that cellular mechanisms must somehow understand where to start reading the gene and where to stop. It turned out that one of the codons is a START CODON, and three more are STOP CODONS. Such codons appear at the beginning and, accordingly, at the end of each gene. If, for example, you remove the start codon from the DNA chain before a gene, then this gene will never be read.

The table attached to this post contains almost all of our genetic code. A simple thing, four by four cells, but obtaining this information gave a gigantic impetus to the development of genetics and related sciences.
(In this table, uracil (U) is indicated instead of thymine (T), since in RNA, which is a mirror copy of a gene, uracil is used instead of thymine - this makes it easier for us and cellular mechanisms to distinguish DNA from RNA - this is very important so as not to accidentally start spoil DNA instead of processing RNA).

Now let's walk around this table a little.

Some amino acids are encoded by two, others by four or even six codons, and only one amino acid, tryptophan, is encoded by just one codon. This distribution of codons is not accidental, otherwise natural selection would have destroyed it long ago. In general, every time some property of a living being seems incomprehensibly absurd to you, it is worth remembering that evolution does not tolerate imperfections and excesses: what does not in some way benefit the organism or the species as a whole does not last long.

Often codons designating the same amino acid differ only in the last letter. This is a print ancient history: The very first living creatures were much more primitive than the simplest ones existing at the moment, and made do with much less amino acids in their cells. So a two-letter code made up of the same four nucleotides was quite enough for them. But then it turned out that in the broth surrounding these creatures there were some other useful things that would be nice to use in the household. In order to use all the available and useful amino acids, the two-letter code was no longer enough, and our distant ancestors had to sacrifice bonds and expand their alphabet.

The fact that some codons differ only in the last amino acid gives us special stability. If an error is made when copying DNA, and if our correction tools miss it, then, for example, instead of CCT there will be CCT or CCA - but we don’t care! Because all these codons correspond to the same amino acid - proline, and the protein will be built correctly in this place.

Due to the fact that all living creatures on Earth use this particular genetic code (there are some exceptions in the world of microorganisms), it becomes possible to exchange genes between different types. You can put the DNA of one creature into the cell of another, and it will be successfully read, and the production of completely specific proteins or RNA will begin. This is what bacteria do when they exchange genes with each other in the process of horizontal transfer. This is what viruses do when they inject their DNA into the cell of another organism. The unity of the genetic language leads to the fact that life on Earth is in a state of amazing physiological harmony (those who have a stomach ache today may miss this phrase).

Now you have the most basic knowledge of the genetic code, and our other articles about the work of genes, proteins, RNA, etc. will be much easier to understand.

The mark of the creator Filatov Felix Petrovich

Chapter 496. Why are there twenty coded amino acids? (XII)

Why are there twenty coded amino acids? (XII)

It may seem to an inexperienced reader that the elements of the genetic coding machine were described in such detail in the previous chapter that by the end of reading he even began to get tired somehow, feeling that the beginning of the book, which somewhat intrigued him, turns into pages from a high school textbook that can dishearten anyone who remembers his native school. The experienced Reader, on the contrary, knows everything that has been told well, and he, sinfully, is thinking about whether to write a more recent textbook himself - for the same senior classes. Without thinking of amusing the proud world– in other words, without intending to bore either one, the Author would like to emphasize that he understands: the devil is in the details. But there are so many of them in molecular biology that any formalization seems like an outrageous simplification. However, it often happens that the temptation to formalize is irresistible, and here the Author cannot deny himself the pleasure of once again quoting the Spanish philosopher José Ortega y Gasset:

« Gray color is ascetic. This is its symbolism in everyday language, and Goethe hints at this symbol: “Theory, my friend, is dry, but the tree of life turns green.” The most that a color that does not want to be a color can do is become gray; but life seems like a green tree - what an extravagance!.. The elegant desire to prefer the color gray to the wonderful and contradictory color extravagance of life leads us to theorizing. In theory, we exchange reality for that aspect of it, which are concepts. Instead of living in it, we think about it. But who knows if behind this obvious asceticism and withdrawal from life, which is pure thinking, the most complete form of vitality, its highest luxury?

- Bravo, Jose! That’s exactly what I think – I’m even convinced of it.

The main, although smaller in volume, remainder of the book, to which the Author now turns, is devoted to formalization, theorizing, schemes, and design of the genetic code. The first formal hypothesis of the structure of the genetic code provides a possible answer to the question why there are exactly twenty encoded amino acids .

In 1954, Gamow was the first to show that " when 4 nucleotides are combined in triplets, 64 combinations are obtained, which is quite enough to record hereditary information" He was the first to propose that amino acids are encoded by triplets of nucleotides and expressed the hope that “Some of the younger scientists will live to see it [the genetic code] deciphered”. In 1968, Americans Robert Holley, Har Korana and Marshall Nirenberg received Nobel Prize for deciphering the genetic code. The prize was awarded after the death of George Gamow in the same year four months earlier.

The numbers 64 (theoretical code capacity) and 20 (actual coding capacity, that is, the number of encoded amino acids) form the ratio of combinatorics rules for placements and combinations with repeats: number A of placements (ordered sets) with repeats from r (r = 3; codon size) elements of a set M containing k (k = 4; number of bases) elements is equal to

A k r= k r= A 4 3= 64,

and the number C of combinations with repetitions of k elements in r, i.e., any subset of 3 elements of a set containing 4 elements, is equal to:

With k r= [(k+r-1)!] : = C 4 3= 20.

This immediately leads to the idea that the evolution of the genetic code could begin with the stage of “set” coding, when the product was encoded not by the sequence of triplet bases, but by their set, that is, two groups of codons, such as, for example, SAA, ASA, AAS or TGC, TCG, GCT, GTC, CTG, CGT were functionally equivalent (within the group) and each directed the synthesis of the same amino acid. Similar considerations come to mind when reading the work of Ishigami and Nagano (1975), with their idea that each primary amino acid could correspond to a wide range of codons, and of Folsom (1977) and Trainor (1984), with their idea of ​​base permutation within triplet. Obviously, a smaller number of codons did not provide the required diversity of products, and b O The rest was redundant and, at least, did not correspond to the number of amino acids known today. At one time we also made a (very) modest contribution to these ideas, noting that the number of combinations of 4 By 3 with repetitions illustrated by number quantum states A three-particle Bose gas with four probable quantum eigenstates54.

Later, Gamow proposed a scheme for implementing the genetic code, which involved the assembly of a polypeptide directly on a DNA molecule. According to this model, each amino acid is placed in a rhombic indentation between four nucleotides, two from each of the complementary chains. Although such a diamond consists of four nucleotides and, therefore, the number of combinations is 256, due to restrictions associated with hydrogen bonds of nucleotide residues, just 20 variants of such diamonds are possible. This scheme, called diamond code, suggests a correlation between successive amino acid residues, since two nucleotides always appear in two adjacent diamonds (overlapping code). Further research showed, however, that this Gamow model also does not agree with experimental data.

If the capacity of the genetic code were used without reserve, that is, only one amino acid corresponded to each triplet, its security would be very doubtful: any nucleotide mutation could be catastrophic. In the case of the current version, a third of random point mutations occur in the last letters of the codons, half of which (codons of the octet I) is not sensitive to mutations at all: the third letter of the codon can be any of the four - T, C, A or G. Resistance to point mutations of octet codons II is largely determined by two factors - (1) the possibility of arbitrary replacement of the third base (albeit when choosing only from two - either purines or pyrimidines), which does not change the encoded amino acid at all, and (2) the possibility of replacing purines with pyrimidines and vice versa, which preserves similar hydrophilicity/hydrophobicity of products, although it does not preserve their mass. Thus, Nature uses an extremely successful “backlash” called degeneracy code, when the encoded character corresponds to more than one encoding character.

Evolution successively refined the functions of each of the three bases of the codon, which ultimately led to strict tripletity of only two codons: ATG- For M(methionine) and TTG- For W(tryptophan). Based on the triplet’s ability to encode only one amino acid, we classify these two as the degeneracy group I. When the product is encoded by a fixed doublet of bases, and the third can be any of four possible and actually serves as a separator between functional doublets, they speak of amino acids of the degeneracy group IV; There are eight such amino acids: alanine, A, arginine, R, valine, V, glycine, G, leucine, L, proline, P, serine, S, threonine, T. The generalized codon for each amino acid in this group, for example, leucine, is written as follows: STN (N -arbitrary basis).

Twelve encoded products belong to the degeneracy group II; in this group the third base is one of two (not from four, as in the previous case): this is purine ( R), that is, either adenine, A, or guanine, G, – or pyrimidine ( Y), that is, either cytosine, WITH, or thymidine, T. This group includes three amino acids familiar to us from the fourth degeneracy group - arginine, leucine and serine, but encoded here by other doublets, two pairs - asparagine / aspartic acid ( N/D), and glutamine/glutamic acid ( Q/E), as well as histidine H, lysine K, and tyrosine Y. The universal genetic code also includes cysteine ​​in this group. WITH, with its two coding triplets – TGC And TGT, that is, with a third pyrimidine, as well as three stop codons, TAG, TAA And TGA, which only work as punctuation marks, fixing the end of the gene, but not encoding any amino acid. The generalized codon for amino acids of this group, for example, asparagine, is written as follows: AAY, and aspartic acid – G.A.R..

Finally, the degeneracy group III contains isoleucine, encoded three triplets ATA, ATC And A.T.T.. Grounds A, WITH And T, third in codons for I, have a common symbol N, so the generalized isoleucine codon is written as follows: ATN. All these features of the code are well illustrated by the table above.

It is curious that the molecular weight of the encoded amino acid is inversely dependent on the number of the degeneracy group to which it belongs (V. Shcherbak). This is the first evidence of apparent involvement noted here molecular weight components of the genetic code to its rational organization.

In the table above, the ordering by increasing molecular weight refers to the amino acids in the composition ordered by numbers of degeneracy groups (Roman numerals), grouped into two octets (Arabic numerals). In this case, the position of cysteine WITH corrected, which will be discussed in the next chapter; We will also talk about octets there.

Returning to the choice twenty amino acids for coding, it is worth noting another interesting circumstance: this choice could also be determined by quantum information theory, which proposes an optimal algorithm (Grover's algorithm) for packaging and reading the information content of DNA (Apoorva Patel, 2001). This algorithm determines the number of objects N, distinguished by the number of responses Not really to questions Q, in the following way:

(2Q +1) sin -1 (1 / ?N ) = ? /2 .

Solutions of this equation for small values Q very characteristic:

Q= 1ln N= 04.0

Q= 2ln N= 10.5

Q= 3ln N= 20.2.

In theory, these values ​​do not have to be integers. Interestingly, to a first approximation, they correspond to the sequence of tetrahedral numbers, as well as the evolution of the functional codon size from singlet to triplet. In other words, a tetrahedron can also be built from ten and from four monomers; These numbers are marked in the solutions of the above equation. Later we will show that the combination of dimensional parameters of amino acids and nucleotides, based on the rules we propose, leads to the spatial equilibrium of a tetrahedron of twenty monomers corresponding to these amino acids. Here it is perhaps worth recalling the still relevant words of V?se (1973): “ It seems almost a cruel joke that Nature should choose such a number[coded] amino acids, which is easily obtained as a result of many

mathematical operations" But, one way or another, twenty alpha amino acids (out of hundreds found in nature) turned out to be enough to provide the necessary diversity of proteins.

…………………

Number 496 , which marks this chapter, is interesting in that it belongs to the class of so-called perfect numbers and that's the only thing three-digit perfect number. A perfect number is a natural number equal to the sum of all its own divisors (that is, all positive divisors other than the number itself). Sum of all divisors of a number 496 , that is, 1+2+4+8+16+31+62+124+248, is equal to itself. We remembered perfect numbers and note the uniqueness of this particular number, because, firstly, it is three-digit - like the three-digit coding elements we are talking about, and secondly, like all the previous numbers mentioned here, it is random or not – characterizes one of the formal parameters of the genetic code, which we will discuss further. The reader’s patience is not unlimited, and the Author recalls in this regard an excerpt from a letter from one of the readers to the famous popularizer of mathematics Martin Gardner: Stop looking for interesting numbers! Leave at least one uninteresting number for interest! But the temptation is great, and it is difficult to resist.

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