The genetic code is a specific sequence. Genetic code as a way to record hereditary information
Lecture 5. Genetic code
Definition of the concept
The genetic code is a system for recording information about the sequence of amino acids in proteins using the sequence of nucleotides in DNA.
Since DNA is not directly involved in protein synthesis, the code is written in RNA language. RNA contains uracil instead of thymine.
Properties of the genetic code
1. Triplety
Each amino acid is encoded by a sequence of 3 nucleotides.
Definition: a triplet or codon is a sequence of three nucleotides encoding one amino acid.
The code cannot be monoplet, since 4 (the number of different nucleotides in DNA) is less than 20. The code cannot be doublet, because 16 (the number of combinations and permutations of 4 nucleotides of 2) is less than 20. The code can be triplet, because 64 (the number of combinations and permutations from 4 to 3) is more than 20.
2. Degeneracy.
All amino acids, with the exception of methionine and tryptophan, are encoded by more than one triplet:
2 AK for 1 triplet = 2.
9 AK, 2 triplets each = 18.
1 AK 3 triplets = 3.
5 AK of 4 triplets = 20.
3 AK of 6 triplets = 18.
A total of 61 triplets encode 20 amino acids.
3. Presence of intergenic punctuation marks.
Definition:
Gene - a section of DNA that encodes one polypeptide chain or one molecule tRNA, rRNA orsRNA.
GenestRNA, rRNA, sRNAproteins are not coded.
At the end of each gene encoding a polypeptide there is at least one of 3 triplets encoding RNA stop codons, or stop signals. In mRNA they have the following form: UAA, UAG, UGA . They terminate (end) the broadcast.
Conventionally, the codon also belongs to punctuation marks AUG - the first after the leader sequence. (See Lecture 8) It functions as a capital letter. In this position it encodes formylmethionine (in prokaryotes).
4. Unambiguity.
Each triplet encodes only one amino acid or is a translation terminator.
The exception is the codon AUG . In prokaryotes, in the first position (capital letter) it encodes formylmethionine, and in any other position it encodes methionine.
5. Compactness, or absence of intragenic punctuation marks.
Within a gene, each nucleotide is part of a significant codon.
In 1961, Seymour Benzer and Francis Crick experimentally proved the triplet nature of the code and its compactness.
The essence of the experiment: “+” mutation - insertion of one nucleotide. "-" mutation - loss of one nucleotide. A single "+" or "-" mutation at the beginning of a gene spoils the entire gene. A double "+" or "-" mutation also spoils the entire gene.
A triple “+” or “-” mutation at the beginning of a gene spoils only part of it. A quadruple “+” or “-” mutation again spoils the entire gene.
The experiment proves that The code is transcribed and there is no punctuation marks inside the gene. The experiment was carried out on two adjacent phage genes and showed, in addition, presence of punctuation marks between genes.
6. Versatility.
The genetic code is the same for all creatures living on Earth.
In 1979, Burrell opened ideal human mitochondria code.
Definition:
It's called "ideal" genetic code, in which the rule of degeneracy of the quasi-doublet code is satisfied: If in two triplets the first two nucleotides coincide, and the third nucleotides belong to the same class (both are purines or both are pyrimidines), then these triplets code for the same amino acid.
There are two exceptions to this rule in the universal code. Both deviations from the ideal code in the universal relate to fundamental points: the beginning and end of protein synthesis:
Codon | Universal code | Mitochondrial codes |
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Vertebrates | Invertebrates | Yeast | Plants |
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STOP | STOP |
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With UA | |||||
A G A | STOP | ||||
STOP | 230 substitutions do not change the class of the encoded amino acid. to tearability. In 1956, Georgiy Gamow proposed a variant of the overlapping code. According to the Gamow code, each nucleotide, starting from the third in the gene, is part of 3 codons. When the genetic code was deciphered, it turned out that it was non-overlapping, i.e. Each nucleotide is part of only one codon. Advantages of an overlapping genetic code: compactness, less dependence of the protein structure on the insertion or deletion of a nucleotide. Disadvantage: the protein structure is highly dependent on nucleotide replacement and restrictions on neighbors. In 1976, the DNA of phage φX174 was sequenced. It has single-stranded circular DNA consisting of 5375 nucleotides. The phage was known to encode 9 proteins. For 6 of them, genes located one after another were identified. It turned out that there is an overlap. Gene E is located entirely within the gene D . Its start codon results from a frame shift of one nucleotide. Gene J starts where the gene ends D . Start codon of the gene J overlaps with the stop codon of the gene D as a result of a shift of two nucleotides. The construction is called a “reading frame shift” by a number of nucleotides not a multiple of three. To date, overlap has only been shown for a few phages. Information capacity of DNA There are 6 billion people living on Earth. Hereditary information about them 4x10 13 book pages. These pages would take up the space of 6 NSU buildings. 6x10 9 sperm take up half a thimble. Their DNA takes up less than a quarter of a thimble. | ||||
The genetic code, expressed in codons, is a system for encoding information about the structure of proteins, inherent in all living organisms on the planet. It took a decade to decipher it, but science understood that it existed for almost a century. Universality, specificity, unidirectionality, and especially the degeneracy of the genetic code are important biological significance.
History of discoveries
The problem of coding has always been key in biology. Science has moved rather slowly towards the matrix structure of the genetic code. Since the discovery of the double helical structure of DNA by J. Watson and F. Crick in 1953, the stage of unraveling the very structure of the code began, which prompted faith in the greatness of nature. Linear structure proteins and the same DNA structure implied the presence of a genetic code as a correspondence between two texts, but written using different alphabets. And if the alphabet of proteins was known, then the signs of DNA became the subject of study by biologists, physicists and mathematicians.
There is no point in describing all the steps in solving this riddle. A direct experiment that proved and confirmed that there is a clear and consistent correspondence between DNA codons and protein amino acids was carried out in 1964 by C. Janowski and S. Brenner. And then - the period of deciphering the genetic code in vitro (in a test tube) using protein synthesis techniques in cell-free structures.
The fully deciphered code of E. Coli was made public in 1966 at a symposium of biologists in Cold Spring Harbor (USA). Then the redundancy (degeneracy) of the genetic code was discovered. What this means is explained quite simply.
Decoding continues
Obtaining data on deciphering the hereditary code was one of the most significant events of the last century. Today, science continues to in-depth study the mechanisms of molecular encodings and its systemic features and excess of signs, which expresses the degeneracy property of the genetic code. A separate branch of study is the emergence and evolution of the system for coding hereditary material. Evidence of the connection between polynucleotides (DNA) and polypeptides (proteins) gave impetus to the development of molecular biology. And that, in turn, to biotechnology, bioengineering, discoveries in breeding and plant growing.
Dogmas and rules
The main dogma of molecular biology is that information is transferred from DNA to messenger RNA, and then from it to protein. In the opposite direction, transfer is possible from RNA to DNA and from RNA to another RNA.
But the matrix or basis always remains DNA. And all other fundamental features of information transmission are a reflection of this matrix nature of transmission. Namely, transmission through the synthesis of other molecules on the matrix, which will become the structure for the reproduction of hereditary information.
Genetic code
Linear coding of the structure of protein molecules is carried out using complementary codons (triplets) of nucleotides, of which there are only 4 (adeine, guanine, cytosine, thymine (uracil)), which spontaneously leads to the formation of another chain of nucleotides. Same number and the chemical complementarity of nucleotides is the main condition for such synthesis. But when a protein molecule is formed, there is no quality match between the quantity and quality of monomers (DNA nucleotides are protein amino acids). This is natural hereditary code- a system for recording in a sequence of nucleotides (codons) the sequence of amino acids in a protein.
The genetic code has several properties:
- Tripletity.
- Unambiguity.
- Directionality.
- Non-overlapping.
- Redundancy (degeneracy) of the genetic code.
- Versatility.
Let's give brief description, focusing on biological significance.
Triplety, continuity and the presence of stop signals
Each of the 61 amino acids corresponds to one sense triplet (triplet) of nucleotides. Three triplets do not carry amino acid information and are stop codons. Each nucleotide in the chain is part of a triplet and does not exist on its own. At the end and at the beginning of the chain of nucleotides responsible for one protein, there are stop codons. They start or stop translation (the synthesis of a protein molecule).
Specificity, non-overlap and unidirectionality
Each codon (triplet) codes for only one amino acid. Each triplet is independent of its neighbor and does not overlap. One nucleotide can be included in only one triplet in the chain. Protein synthesis always proceeds in only one direction, which is regulated by stop codons.
Redundancy of the genetic code
Each triplet of nucleotides codes for one amino acid. There are 64 nucleotides in total, of which 61 encode amino acids (sense codons), and three are nonsense, that is, they do not encode an amino acid (stop codons). The redundancy (degeneracy) of the genetic code lies in the fact that in each triplet substitutions can be made - radical (lead to the replacement of an amino acid) and conservative (do not change the class of the amino acid). It is easy to calculate that if 9 substitutions can be made in a triplet (positions 1, 2 and 3), each nucleotide can be replaced by 4 - 1 = 3 other options, then total quantity possible options nucleotide substitutions will be 61 by 9 = 549.
The degeneracy of the genetic code is manifested in the fact that 549 variants are much more than are needed to encode information about 21 amino acids. Moreover, out of 549 variants, 23 substitutions will lead to the formation of stop codons, 134 + 230 substitutions are conservative, and 162 substitutions are radical.
Rule of degeneracy and exclusion
If two codons have two identical first nucleotides, and the remaining ones are represented by nucleotides of the same class (purine or pyrimidine), then they carry information about the same amino acid. This is the rule of degeneracy or redundancy of the genetic code. Two exceptions are AUA and UGA - the first encodes methionine, although it should be isoleucine, and the second is a stop codon, although it should encode tryptophan.
The meaning of degeneracy and universality
It is these two properties of the genetic code that have the greatest biological significance. All the properties listed above are characteristic of the hereditary information of all forms of living organisms on our planet.
The degeneracy of the genetic code has adaptive significance, like multiple duplication of the code for one amino acid. In addition, this means a decrease in significance (degeneration) of the third nucleotide in the codon. This option minimizes mutational damage in DNA, which will lead to gross disturbances in the structure of the protein. This defense mechanism living organisms on the planet.
Gene- structural and functional unit of heredity that controls development a certain sign or properties. Parents pass on a set of genes to their offspring during reproduction. Russian scientists made a great contribution to the study of the gene: Simashkevich E.A., Gavrilova Yu.A., Bogomazova O.V. (2011)
Currently, in molecular biology it has been established that genes are sections of DNA that carry some kind of integral information - about the structure of one protein molecule or one RNA molecule. These and other functional molecules determine the development, growth and functioning of the body.
At the same time, each gene is characterized by a number of specific regulatory DNA sequences, such as promoters, which are directly involved in regulating the expression of the gene. Regulatory sequences can be located either in close proximity to the open reading frame encoding a protein, or to the beginning of an RNA sequence, as is the case with promoters (the so-called cis cis-regulatory elements), and over distances of many millions of base pairs (nucleotides), as in the case of enhancers, insulators and suppressors (sometimes classified as trans-regulatory elements, English. trans-regulatory elements). Thus, the concept of a gene is not limited only to the coding region of DNA, but is a broader concept that also includes regulatory sequences.
Originally the term gene appeared as a theoretical unit for the transmission of discrete hereditary information. The history of biology remembers disputes about which molecules can be carriers of hereditary information. Most researchers believed that only proteins could be such carriers, since their structure (20 amino acids) allows for the creation of more variants than the structure of DNA, which is composed of only four types nucleotides. Later it was experimentally proven that it is DNA that includes hereditary information, which was expressed as the central dogma of molecular biology.
Genes can undergo mutations - random or targeted changes in the sequence of nucleotides in the DNA chain. Mutations can lead to a change in sequence, and therefore a change biological characteristics protein or RNA, which in turn may result in general or local altered or abnormal functioning of the body. Such mutations in some cases are pathogenic, since they result in disease, or lethal at the embryonic level. However, not all changes in the nucleotide sequence lead to changes in protein structure (due to the effect of degeneracy of the genetic code) or to significant change sequences and are not pathogenic. In particular, the human genome is characterized by single nucleotide polymorphisms and copy number variations. copy number variations), such as deletions and duplications, which account for about 1% of the entire human nucleotide sequence. Single nucleotide polymorphisms, in particular, define different alleles of a single gene.
The monomers that make up each DNA strand are complex organic compounds, including nitrogenous bases: adenine (A) or thymine (T) or cytosine (C) or guanine (G), pentaatomic sugar-pentose-deoxyribose, after which DNA itself was named, as well as a phosphoric acid residue. These compounds are called nucleotides.
Gene properties
- discreteness - immiscibility of genes;
- stability - the ability to maintain structure;
- lability - the ability to mutate repeatedly;
- multiple allelism - many genes exist in a population in multiple molecular forms;
- allelicity - in the genotype of diploid organisms there are only two forms of the gene;
- specificity - each gene encodes its own trait;
- pleiotropy - multiple effect of a gene;
- expressivity - the degree of expression of a gene in a trait;
- penetrance - the frequency of manifestation of a gene in a phenotype;
- amplification - increasing the number of copies of a gene.
Classification
- Structural genes are unique components of the genome, representing a single sequence that encodes a specific protein or certain types of RNA. (See also the article genes household).
- Functional genes - regulate the functioning of structural genes.
Genetic code- 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 literature). In DNA and RNA molecules, nucleotides are arranged in chains and, thus, sequences of genetic letters are obtained.
Genetic code
To build proteins in nature, 20 different amino acids are used. Each protein is a chain or several chains of amino acids in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all of its biological properties. The set of amino acids is also universal for almost all living organisms.
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 mRNA). 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
- Triplety- a meaningful unit of code is a combination of three nucleotides (triplet, or codon).
- Continuity- there are no punctuation marks between triplets, that is, the information is read continuously.
- 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, which encode several frameshift proteins).
- Uniqueness (specificity)- a specific codon corresponds to only one amino acid (however, the UGA codon has Euplotes crassus encodes two amino acids - cysteine and selenocysteine)
- Degeneracy (redundancy)- several codons can correspond to the same amino acid.
- Versatility- the genetic code works the same in organisms different levels complexity - from viruses to humans (methods are based on this genetic engineering; There are a number of exceptions, shown in the table in the Variations in the Standard Genetic Code section below).
- Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical.
Protein biosynthesis and its stages
Protein biosynthesis- a complex multi-stage process of synthesis of a polypeptide chain from amino acid residues, occurring on the ribosomes of the cells of living organisms with the participation of mRNA and tRNA molecules.
Protein biosynthesis can be divided into the stages of transcription, processing and translation. During transcription, genetic information encrypted in DNA molecules is read and this information is written into mRNA molecules. During a series of successive processing stages, some fragments that are unnecessary in subsequent stages are removed from the mRNA, and nucleotide sequences are edited. After transporting the code from the nucleus to the ribosomes, the actual synthesis of protein molecules occurs by attaching individual amino acid residues to the growing polypeptide chain.
Between transcription and translation, the mRNA molecule undergoes a series of sequential changes that ensure the maturation of the functioning matrix for the synthesis of the polypeptide chain. A cap is attached to the 5΄-end, and a poly-A tail is attached to the 3΄-end, which increases the lifespan of the mRNA. With the advent of processing in the eukaryotic cell, it became possible to combine gene exons to obtain more variety proteins encoded by a single sequence of DNA nucleotides - alternative splicing.
Translation consists of the synthesis of a polypeptide chain in accordance with the information encoded in messenger RNA. The amino acid sequence is arranged using transport RNA (tRNA), which forms complexes with amino acids - aminoacyl-tRNA. Each amino acid has its own tRNA, which has a corresponding anticodon that “matches” the mRNA codon. During translation, the ribosome moves along the mRNA, and as it does so, the polypeptide chain grows. Energy for protein biosynthesis is provided by ATP.
The finished protein molecule is then cleaved from the ribosome and transported to the desired location in the cell. To achieve their active state, some proteins require additional post-translational modification.
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- This certain combinations nucleotides and the sequence of their location in the DNA molecule. This is a method characteristic of all living organisms of encoding the amino acid sequence of proteins using a sequence of nucleotides.
DNA uses four nucleotides - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian literature are designated by the letters A, G, T and C. These letters make up the alphabet of the genetic code. RNA uses the same nucleotides, with the exception of thymine, which is replaced by a similar nucleotide - uracil, which is designated by the letter U (U in Russian literature). In DNA and RNA molecules, nucleotides are arranged in chains and, thus, sequences of genetic letters are obtained.
Genetic code
To build proteins in nature, 20 different amino acids are used. Each protein is a chain or several chains of amino acids in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all 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 simultaneously be part of two or more triplets.
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 - complex process, depending 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 transformation of primary products of transcription and translation into functioning molecules. Functionally inactive precursor molecules are exposed to P. ribonucleic acid(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 ability to adapt to conditions environment 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 coli 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 medium, and therefore in the cell, decreases, and lactose increases, the following events occur: the amount of cyclic adenosine monophosphate increases, it binds to the CAP protein - this complex activates the promoter to which RNA polymerase binds; at the same time, excess lactose binds to the repressor protein and releases the operator from it - the path is open for RNA polymerase, transcription of the structural genes of the lac operon begins. Lactose acts as an inducer of the synthesis of those enzymes that break it down.
5) Regulation of gene expression in eukaryotes is much more complicated. Various types cells of a multicellular eukaryotic organism synthesize a number of identical proteins and at the same time they differ from each other in a set of cell-specific proteins of this type. The level of production depends on the cell type, as well as the stage of development of the organism. Regulation of gene expression occurs 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 not always associated with broadcasting. The synthesized mRNA can long time stored 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 important has the effect of sex hormones.
10. In eukaryotes, at each stage of ontogenesis, 5-10% of genes are expressed, the rest must be blocked.
6) reparation genetic material
Genetic reparation- the process of eliminating genetic damage and restoring the hereditary apparatus, occurring in the cells of living organisms under the influence of special enzymes. The ability of cells to repair genetic damage was first discovered in 1949 by the American geneticist A. Kellner. Repair - special function cells, which consists in the ability to correct chemical damage and breaks in DNA molecules damaged during normal DNA biosynthesis in the cell or as a result of exposure to physical or chemical agents. It is carried out by special enzyme systems of the cell. A number of hereditary diseases (eg, xeroderma pigmentosum) are associated with disorders of repair systems.
types of reparations:
Direct repair is the simplest way to eliminate damage in DNA, which usually involves specific enzymes that can quickly (usually in one stage) eliminate the corresponding damage, restoring the original structure of nucleotides. This is the case, for example, with O6-methylguanine DNA methyltransferase, which removes a methyl group from a nitrogenous base onto one of its own cysteine residues.
The genetic code 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.
This 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, in the structure of the code one can trace traces of its evolution, from the moment of its inception to today.
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 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 3 nucleotides 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, about good condition blood, oh normal hemoglobin The GAA triplet, who is in sixth place in the chain, can tell the doctors. 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.
