DNA and protein coding system. Coding and implementation of biological information in a cell, genetic code and its properties. Need help learning a topic
Genetic code is a system for recording genetic information in DNA molecules about the structure of a protein molecule. Protein consists of amino acids, which are only 20. AAs in a protein molecule are arranged in a linear order, like nucleotides in a DNA molecule. The sequence of AK in a protein is defined by a sequence of nucleotides in a DNA molecule, its gene code. Properties of the code 1) Triplet - Each amino acid is encoded by three nucleotides. A triplet of nucleotides is called a codon. 2) Non-overlapping - triplets follow one after another. Each nucleotide is included in only one codon. Triplets do not overlap. 2) Unidirectionality - Genetic information is read in 3 nucleotides in one direction, without any insertions between nucleotides. 4) Expressiveness (redundancy) - 1 the presence of excess triplets necessary for coding amino acids. 2 The presence of "nonsense" codons UAA UAG UGA-termination codons, AUG and GUG initiation codons. 5) Universality - in all living organisms, the same amino acids are encoded by the same triplets. 6) specificity. There are no cases when one and the same de codon would correspond to several AKs.
16. Protein biosynthesis is a complex multistage process of synthesis of a polypeptide chain from amino acids that occurs on ribosomes with the participation of mRNA and tRNA molecules. The process of protein biosynthesis requires significant energy consumption.
Protein synthesis includes several stages:
1. Pretranscriptional. This is the starting stage of synthesis, during which the DNA molecule is activated with the help of special proteins.
2. Transcriptional-synthesis of i-RNA occurs in the nucleus, during which the information contained in the DNA gene is rewritten into i-RNA with a sequence of nucleotides complementary to the DNA molecule.
3. Transport covers the period between transcription and broadcast. Above this stage, processing takes place, i.e. maturation of I-RNA. Its essence is the removal of introns (non-informal areas). Exaons (triplets carrying information about AK) are preserved and connected into a single chain with the help of ligase enzymes. This phenomenon is called splicing. The spliced m-RNA is transferred from the nucleus to the cytoplasm using carrier proteins.
4. Translation is the synthesis of the polypeptide chain from AK according to the coding m-RNA. In the course of translation, the translation of genetic information into the amino acid sequence occurs: DNA, i-RNA, protein. The following stages stand out here: initiation, elongation, termination.
initiation - recognition of the start codon by the ribosome and the beginning of synthesis.
elongation is actually protein synthesis.
termination - recognition of a termination codon (stop codon) and product separation.
Thus, in the process of protein biosynthesis, new protein molecules are formed in accordance with the exact information stored in the DNA. This process ensures the renewal of proteins, metabolic processes, the growth and development of cells, that is, all the processes of cell life.
17. Translation is the synthesis of a polypeptide chain from AK according to the coding i-RNA. In the course of translation, the translation of genetic information into the amino acid sequence occurs: DNA, i-RNA, protein. Translational is a very important part of the overall metabolism of the cell. At least 20 enzymes (aminoacyl synthetases), up to 60 different t-RNAs, 3-5 r-RNA molecules and i-RNA macromolecules are involved in it. The following stages stand out here: initiation, elongation, termination.
Initiation - the beginning of the broadcast. A whole ribosome is formed, mRNA is attached, and the first amino acid is established. In the process of translation, ribosomes are in a “assembled” state. In a whole ribosome, a tRNA attachment site is isolated, "loaded" with an amino acid (i.e., aminoacyl-tRNA) - an acceptor (A-site) and a tRNA retention site with a growing polypeptide chain - peptidyl (P-site) (in molecular biology, the expression “site chains "are often replaced by the term" site "). During initiation (with the participation of three auxiliary protein factors), mRNA binds to the small subunit of the ribosome, then the “loaded” (carrying the amino acid) tRNA is attached to the first codon with its anticodon, and then the large ribosome subunit is attached to the formed complex.
2. Elongation. Another aminoacyl-tRNA is attached to the second codon (in the A-site of the ribosome). A peptide bond is formed between the carboxyl group (-COOH) of the first amino acid and the amino group (-NH,) of the second. After that, the first amino acid is detached from its tRNA and "hangs" on the second tRNA amino acid connected to it. The empty first tRNA is released from the complex with the ribosome, and the P-site becomes unoccupied. The ribosome “makes a step” along the mRNA. In this case, tRNA with amino acids moves from the A site to the P site. The “step” of the ribosome is always strictly defined and is equal to three nucleotides (codon). The movement of the ribosome along the mRNA is called a translocation. Like replication and transcription, translocation always occurs in the 5 "- 3" direction of the mRNA.
3. Termination. The synthesis of the polypeptide chain continues until the ribosome reaches one of the three stop codons. At this point, the protein chain is detached and the ribosome dissociates into subunits. Almost all proteins at the end of their synthesis undergo maturation or processing - reactions of post-translational modifications. After that, they (mainly through the "pipeline" of the endoplasmic reticulum) are transported to their destination.
Post-broadcast. The formation of the secondary and tertiary structure of the protein occurs, that is, the formation of the final structure of the protein.
18. Each organism has its own set of proteins that perform the necessary functions and ensure the formation of all the characteristics of the organism. Protein synthesis or the implementation of genetic information occurs in every living cell in accordance with its genetic program, recorded using the genetic code in nucleic acid molecules. Protein synthesis is a complex, multistep process of the formation of a protein molecule (polymer) from amino acids (monomers), which is impossible without the participation of nucleic acids, a large number of enzymes, energy (ATP), ribosomes, amino acids and Mg2 + ions. The gene has a discontinuous structure. The coding regions are exons and the non-coding regions are introns. The gene in eukaryoic organisms has an exon-intron structure. The intron is longer than the exon. In the process of processing, introns are "cut" - splicing. After the formation of a mature m-RNA, after interaction with a special protein, it passes into the system - the informosome, which carries information to the cytoplasm. Now exon-intron systems are well studied (for example, the oncogene - P-53). Sometimes the introns of one gene are exons of another, then splicing is impossible.
Processing. The molecular mechanisms involved in the "maturation" of different types of RNA are called processing. They are carried out in the nucleus before the release of RNA from the nucleus into the cytoplasm.
In the process of "maturation" of mRNA, special enzymes cut out introns and stitch together the active sites that remain (exons). This process is called splicing. Therefore, the nucleotide sequence in the matured IRNA is not entirely complementary to the DNA nucleotides. In IRNA, such nucleotides can stand side by side, complementary to which nucleotides in DNA are located at a considerable distance from one another.
Splicing is a very precise process. Its violation changes the reading frame during translation, which leads to the synthesis of another peptide. The accuracy of intron excision is ensured by the recognition of enzymes of certain signal sequences of nucleotides in the pro-mRNA molecule.
19 . At every moment, 20% of the genes are working in the cell, not all. In the first, the mechanism of turning on and off genes was studied on the bacteria E. coli Jacob and Monod. In 1966, they formulated a hypothesis of automatic regulation of protein synthesis based on the principle of feedback. In an experiment, they proved that in a prokaryotic cell there is an automatic regulation of the work of genes and protein synthesis. Jacob's scheme - Monod. According to their hypothesis, the reading of information from structural genes occurs in blocks, that is, the unit of transcription is the block operon. It includes several structural genes that are involved in the first cascade of reactions. At their head is an operator DNA segment that separates the promoter from the structural genes, and attaches to the cat in the process of polymerase transcription. The cell still has regulatory genes outside the operon that control the synthesis of the repressor protein. It has the role of turning genes on and off by binding to the operator of the operon. A free repressor protein blocks the operator, preventing the passage of polymerase to structural genes. Repression from the operator is removed by the inductor, which is the metabolite that entered the cell (not any, but the one for the cleavage of which enzymes encoded by this operon are needed). The metabolite attracts the repressor protein, forming an inactive complex with it. As a result, the blockade is removed from the operator and the pathway for polymerase is opened.
Georgiev 1972 - regulation of transcription in eukaryotes. Unit
transcription - transcripton, consisting of uninformative (acceptor)
and informative (structural) zones.
Non-informative zone: promoter, initiator, operator genes.
Informative zone: a structural gene with a mosaic exon
intronic structure. Exons are DNA sequences containing information about the structure of the polypeptide, and introns are inserts from uninformative DNA regions. The transcripton ends with a terminator.
The regulation of transcription in eukaryotes is fundamentally the same as in
prokaryote, but it is combinational and is more complex.
20. Genetic engineering, genetic modification technology is a combination of biotechnological methods that make it possible to create synthetic systems at the molecular biological level.
Genetic engineering makes it possible to design functionally active structures in the form of recombinant nucleic acids: recDNA (recDNA) or recRNA (recRNA) - outside biological systems (in vitro), and then introduce them into cells.
The possibility of direct (horizontal) transfer of genetic information from one biological species to another was proved in the experiments of F. Griffith with pneumococci (1928).
However, genetic engineering as a technology of recDNA arose in 1972, when the first recombinant (hybrid) DNA (recDNA) was obtained in the laboratory of P. Berg (Stanford University, USA), in which DNA fragments of the lambda phage and E. coli were combined with circular DNA of the simian virus SV40.
Since the early 1980s. the achievements of genetic engineering are beginning to be used in practice.
Since 1996, genetic modified plants have been used in agriculture.
Genetic Engineering Challenges
The main directions of genetic modification of organisms:
– imparting resistance to pesticides (for example, to certain herbicides);
– imparting resistance to pests and diseases (for example, Bt modification);
– increased productivity (eg rapid growth of transgenic salmon);
– imparting special qualities (for example, changing the chemical composition).
Biotechnology is a discipline that studies the possibilities of using living organisms, their systems or products of their vital activity to solve technological problems, as well as the possibility of creating living organisms with the necessary properties by the method of genetic engineering.
Biotechnology is often referred to as the application of genetic engineering in the XX-XXI centuries, but the term also refers to a wider range of processes for modifying biological organisms to meet human needs, starting with the modification of plants and domesticated animals through artificial selection and hybridization. With the help of modern methods, traditional biotechnological industries have been able to improve the quality of food products and increase the productivity of living organisms.
21. The lifetime of a cell from its formation to the next division or death is called the cell life cycle (LCC). In the GCC of eukaryotic cells of a multicellular organism, several periods (phases) can be distinguished, each of which is characterized by certain morphological and functional features:
- the phase of reproduction and growth
- phase of differentiation
- phase of normal activity
- the phase of aging and cell death.
In the life cycle of a cell, a mitotic cycle can also be distinguished, which includes the preparation of the cell for division and division itself.
The cell cycle is a set of processes including the period of cell preparation for division and division itself. Consists of two stages - the resting stage (interphase) and the division stage (mitosis)
Interphase precedes mitosis and DNA synthesis takes place in it. Cell preparation for division consists of 3 periods 1) Presynthetic 2) Synthetic 3) Postsynthetic
The genetic code is a system for recording hereditary information in nucleic acid molecules, based on a certain alternation of nucleotide sequences in DNA or RNA, forming codons corresponding to amino acids in a protein.
Properties of the genetic code.
The genetic code has several properties.
Tripletness.
Degeneracy or redundancy.
Unambiguity.
Polarity.
Non-overlap.
Compactness.
Versatility.
It should be noted that some authors also propose other properties of the code associated with the chemical characteristics of the nucleotides included in the code or with the frequency of occurrence of individual amino acids in the proteins of the body, etc. However, these properties follow from the above, so we will consider them there.
a. Tripletness. The genetic code, like many complexly organized systems, has the smallest structural and smallest functional unit. A triplet is the smallest structural unit of the genetic code. It consists of three nucleotides. The codon is the smallest functional unit of the genetic code. As a rule, mRNA triplets are called codons. In the genetic code, a codon has several functions. First, its main function is that it encodes one amino acid. Secondly, the codon may not encode an amino acid, but, in this case, it performs a different function (see below). As can be seen from the definition, a triplet is a concept that characterizes elementary structural unit genetic code (three nucleotides). Codon - characterizes elementary semantic unit genome - three nucleotides determine the attachment of one amino acid to the polypeptide chain.
The elementary structural unit was first deciphered theoretically, and then its existence was confirmed experimentally. Indeed, 20 amino acids cannot be encoded with one or two nucleotides. the latter are only 4. Three out of four nucleotides give 4 3 = 64 variants, which more than exceeds the number of amino acids available in living organisms (see Table 1).
The nucleotide combinations shown in Table 64 have two features. First, out of 64 variants of triplets, only 61 are codons and encode any amino acid, they are called sense codons... Three triplets do not encode
amino acids a are stop signals indicating the end of translation. There are three such triplets - UAA, UAG, UGA, they are also called "meaningless" (nonsense codons). As a result of a mutation, which is associated with the replacement of one nucleotide in a triplet with another, a meaningless codon can arise from a sense codon. This type of mutation is called nonsense mutation... If such a stop signal is formed inside the gene (in its informational part), then during protein synthesis in this place the process will be constantly interrupted - only the first (before the stop signal) part of the protein will be synthesized. A person with this pathology will have a lack of protein and symptoms associated with this lack. For example, this kind of mutation was found in the gene encoding the beta-chain of hemoglobin. A shortened inactive hemoglobin chain is synthesized, which is rapidly destroyed. As a result, a hemoglobin molecule devoid of the beta chain is formed. It is clear that such a molecule is unlikely to fully fulfill its duties. A serious illness occurs, developing as a hemolytic anemia (beta-zero thalassemia, from the Greek word "Talas" - the Mediterranean Sea, where this disease was first discovered).
The mechanism of action of stop codons is different from that of sense codons. This follows from the fact that the corresponding tRNAs have been found for all codons encoding amino acids. No tRNAs were found for nonsense codons. Consequently, tRNA is not involved in the process of stopping protein synthesis.
CodonAUG (in bacteria, sometimes GUG) not only encode the amino acid methionine and valine, but alsobroadcast initiator .
b. Degeneracy or redundancy.
61 out of 64 triplets encode 20 amino acids. Such a three-time excess of the number of triplets over the number of amino acids suggests that two coding options can be used in information transfer. Firstly, not all 64 codons can be involved in coding 20 amino acids, but only 20, and, secondly, amino acids can be encoded by several codons. Research has shown that nature has used the latter option.
His preference is obvious. If only 20 out of 64 variants of triplets participated in the coding of amino acids, then 44 triplets (out of 64) would remain non-coding, i.e. meaningless (nonsense codons). Earlier, we pointed out how dangerous the transformation of the coding triplet as a result of mutation into a nonsense codon is for the life of the cell - this significantly disrupts the normal operation of RNA polymerase, ultimately leading to the development of diseases. Currently, in our genome, three codons are meaningless, but now imagine what it would be like if the number of nonsense codons increased by about 15 times. It is clear that in such a situation the transition from normal codons to nonsense codons will be immeasurably higher.
A code in which one amino acid is encoded by several triplets is called degenerate or redundant. Several codons correspond to almost every amino acid. So, the amino acid leucine can be encoded by six triplets - UUA, UUG, CUU, CUTS, CUA, CUG. Valine is encoded by four triplets, phenylalanine by two and only tryptophan and methionine are coded by one codon. The property that is associated with the recording of the same information with different symbols is called degeneracy.
The number of codons assigned to one amino acid correlates well with the frequency of occurrence of the amino acid in proteins.
And this is most likely not accidental. The higher the frequency of occurrence of an amino acid in a protein, the more often the codon of this amino acid is presented in the genome, the higher the probability of its damage by mutagenic factors. Therefore, it is clear that a mutated codon has more chances to encode the same amino acid with its high degeneracy. From these positions, the degeneracy of the genetic code is a mechanism that protects the human genome from damage.
It should be noted that the term degeneracy is used in molecular genetics and in a different sense. So the main part of the information in the codon falls on the first two nucleotides, the base in the third position of the codon turns out to be insignificant. This phenomenon is called “degeneracy of the third base”. The latter feature minimizes the effect of mutations. For example, it is known that the main function of red blood cells is to carry oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. This function is performed by the respiratory pigment - hemoglobin, which fills the entire cytoplasm of the erythrocyte. It consists of a protein part - globin, which is encoded by the corresponding gene. In addition to protein, heme containing iron is included in the hemoglobin molecule. Mutations in globin genes lead to the appearance of various hemoglobin variants. Most often, mutations are associated with replacement of one nucleotide with another and the appearance of a new codon in the gene, which can encode a new amino acid in the hemoglobin polypeptide chain. In a triplet, as a result of mutation, any nucleotide can be replaced - the first, second or third. Several hundred mutations are known to affect the integrity of the globin genes. About 400 of these are associated with the substitution of single nucleotides in the gene and the corresponding amino acid substitution in the polypeptide. Of these, only 100 substitutions lead to instability of hemoglobin and various kinds of diseases from mild to very severe. 300 (approximately 64%) substitution mutations do not affect hemoglobin function and do not lead to pathology. One of the reasons for this is the above-mentioned “degeneracy of the third base”, when the replacement of the third nucleotide in the triplet encoding serine, leucine, proline, arginine and some other amino acids leads to the appearance of a synonym codon encoding the same amino acid. Phenotypically, this mutation will not appear. In contrast, any substitution of the first or second nucleotide in a triplet in 100% of cases leads to the appearance of a new variant of hemoglobin. But even in this case, there may not be severe phenotypic disorders. The reason for this is the replacement of an amino acid in hemoglobin with another one that is similar to the first in its physicochemical properties. For example, if an amino acid with hydrophilic properties is replaced by another amino acid with the same properties.
Hemoglobin consists of the iron porphyrin group of heme (oxygen and carbon dioxide molecules attach to it) and a protein - globin. Adult hemoglobin (HbA) contains two identical -chains and two -chains. Molecule -chain contains 141 amino acid residues, -chain - 146, - and β-chains differ in many amino acid residues. The amino acid sequence of each globin chain is encoded by its own gene. Gene encoding - the chain is located in the short arm of chromosome 16, -gene - in the short arm of chromosome 11. Substitution in the gene encoding - the hemoglobin chain of the first or second nucleotide almost always leads to the appearance of new amino acids in the protein, dysfunction of hemoglobin and severe consequences for the patient. For example, the replacement of “C” in one of the triplets of the CAU (histidine) by “Y” will lead to the appearance of a new triplet of the CAU, which encodes another amino acid - tyrosine. β-chain of histidine polypeptide to tyrosine will destabilize hemoglobin. The disease develops methemoglobinemia. Replacement, as a result of mutation, of glutamic acid for valine in the 6th position -chains are the cause of the most serious disease - sickle cell anemia. Let's not continue the sad list. We only note that when the first two nucleotides are replaced, an amino acid may appear similar in physicochemical properties to the previous one. So, the replacement of the 2nd nucleotide in one of the triplets encoding glutamic acid (GAA) in -chain with "Y" leads to the appearance of a new triplet (GUA) encoding valine, and the replacement of the first nucleotide with "A" forms the AAA triplet encoding the amino acid lysine. Glutamic acid and lysine are similar in physicochemical properties - they are both hydrophilic. Valine is a hydrophobic amino acid. Therefore, replacing hydrophilic glutamic acid with hydrophobic valine significantly changes the properties of hemoglobin, which ultimately leads to the development of sickle cell anemia, while replacing hydrophilic glutamic acid with hydrophilic lysine changes the function of hemoglobin to a lesser extent - patients have a mild form of anemia. As a result of the substitution of the third base, the new triplet can encode the same amino acids as the previous one. For example, if uracil was replaced by cytosine in the CAC triplet and the CAC triplet appeared, then practically no phenotypic changes in humans will be detected. This is understandable, since both triplets encode the same amino acid, histidine.
In conclusion, it is appropriate to emphasize that the degeneracy of the genetic code and the degeneracy of the third base from a general biological point of view are defense mechanisms that are embedded in evolution in the unique structure of DNA and RNA.
v. Unambiguity.
Each triplet (except for the meaningless ones) encodes only one amino acid. Thus, in the direction of the codon - amino acid, the genetic code is unambiguous, in the direction of the amino acid - codon, it is ambiguous (degenerate).
Unambiguous
Amino acid codon
Degenerate
And in this case, the need for unambiguity in the genetic code is obvious. In another variant, during the translation of the same codon, different amino acids would be inserted into the protein chain and, as a result, proteins with different primary structures and different functions would be formed. Cell metabolism would switch to the "one gene - several poipeptides" mode of operation. It is clear that in such a situation the regulatory function of genes would be completely lost.
Polarity
Reading information from DNA and from mRNA occurs only in one direction. Polarity is essential for identifying higher order structures (secondary, tertiary, etc.). We discussed earlier that lower-order structures define higher-order structures. The tertiary structure and structures of a higher order in proteins are formed immediately as soon as the synthesized RNA strand departs from the DNA molecule or the polypeptide strand departs from the ribosome. While the free end of an RNA or polypeptide acquires a tertiary structure, the other end of the chain is still being synthesized on DNA (if RNA is transcribed) or ribosome (if a polypeptide is transcribed).
Therefore, the unidirectional process of reading information (in the synthesis of RNA and protein) is essential not only for determining the sequence of nucleotides or amino acids in the synthesized substance, but for the rigid determination of secondary, tertiary, etc. structures.
e. Non-overlap.
The code can be overlapping and non-overlapping. Most organisms do not have overlapping code. Overlapping code is found in some phages.
The essence of the non-overlapping code is that the nucleotide of one codon cannot be simultaneously the nucleotide of another codon. If the code were overlapping, then a sequence of seven nucleotides (GCCHCUG) could encode not two amino acids (alanine-alanine) (Fig. 33, A), as in the case of a non-overlapping code, but three (if one nucleotide is common) (Fig. . 33, B) or five (if two nucleotides are common) (see Fig. 33, C). In the last two cases, mutation of any nucleotide would lead to a disruption in the sequence of two, three, etc. amino acids.
However, it has been found that a single nucleotide mutation always disrupts the inclusion of one amino acid in the polypeptide. This is a significant argument for the non-overlapping code.
Let us explain this in Figure 34. The bold lines show the triplets encoding amino acids in the case of non-overlapping and overlapping code. Experiments have shown unequivocally that the genetic code is not overlapping. Without going into the details of the experiment, we note that if we replace the third nucleotide in the nucleotide sequence (see Fig. 34)Have (marked with an asterisk) to something else:
1. With a non-overlapping code, the protein controlled by this sequence would have a substitution of one (first) amino acid (marked with asterisks).
2. With an overlapping code in option A, there would be a change in two (first and second) amino acids (marked with asterisks). In option B, the replacement would have affected three amino acids (marked with asterisks).
However, numerous experiments have shown that when one nucleotide in DNA is disturbed, the disturbances in the protein always concern only one amino acid, which is characteristic of a non-overlapping code.
ГЦУГЦУГ ГЦУГЦУГ ГЦУГЦУГ
ГЦУ ГЦУ ГЦУ УГЦ ЦУГ ГЦУ ЦУГ УГЦ ГЦУ ЦУГ
*** *** *** *** *** ***
Alanine - Alanin Ala - Cis - Lei Ala - Lei - Lei - Ala - Lei
A B C
Non-overlapping code Overlapping code
Rice. 34. Scheme explaining the presence of non-overlapping code in the genome (explanation in the text).
The non-overlapping of the genetic code is associated with another property - the reading of information begins from a certain point - the initiation signal. Such an initiation signal in mRNA is the codon encoding the methionine AUG.
It should be noted that humans still have a small number of genes that deviate from the general rule and overlap.
e. Compactness.
There are no punctuation marks between codons. In other words, triplets are not separated from each other, for example, by one meaningless nucleotide. The absence of "punctuation marks" in the genetic code has been proven in experiments.
f. Versatility.
The code is the same for all organisms living on Earth. Direct evidence of the universality of the genetic code was obtained by comparing DNA sequences with the corresponding protein sequences. It turned out that the same sets of code values are used in all bacterial and eukaryotic genomes. There are exceptions, but not many.
The first exceptions to the universality of the genetic code were found in the mitochondria of some animal species. This concerned the UGA terminator codon, which was read in the same way as the UGG codon encoding the amino acid tryptophan. Other more rare deviations from universality have been found.
DNA code system.
The genetic code of DNA consists of 64 triplets of nucleotides. These triplets are called codons. Each codon encodes one of the 20 amino acids used in protein synthesis. This gives some redundancy in the code: most amino acids are encoded by more than one codon.
One codon performs two interrelated functions: it signals the start of translation and encodes the inclusion of the amino acid methionine (Met) into the growing polypeptide chain. The DNA coding system is designed so that the genetic code can be expressed either as RNA codons or DNA codons. RNA codons are found in RNA (mRNA) and these codons are able to read information during the synthesis of polypeptides (a process called translation). But each mRNA molecule acquires a sequence of nucleotides in transcription from the corresponding gene.
All but two amino acids (Met and Trp) can be encoded with 2 to 6 different codons. However, the genome of most organisms shows that certain codons are preferred over others. In humans, for example, alanine is encoded by GCC four times more often than GCG. This probably indicates the greater efficiency of translation of the translation apparatus (for example, the ribosome) for some codons.
The genetic code is almost universal. The same codons are assigned to the same amino acid site and the same start and stop signals overwhelmingly coincide in animals, plants, and microorganisms. However, some exceptions were found. Most of these involve assigning one or two of the three stop codons to the amino acid.
Russian scientists have found that DNA hides encoded information, the presence of which makes a person to be considered a biological computer, which consists of complex programs.
Experts from the Institute of Quantum Genetics are trying to decipher the mysterious text in DNA molecules. And their discoveries are more and more convincing that at first there was the Word, and we are a product of the vacuum Superbrain. This was told by the President of the ICG Petr Petrovich Gariaev.
More recently, scientists have come to an unexpected discovery: the DNA molecule consists not only of genes responsible for the synthesis of certain proteins and genes responsible for the shape of the face, ear, eye color, etc., but mostly of encoded texts.
Moreover, these texts occupy 95-99 percent of the total chromosome content! ( NOTE: Western scholars consider this an unnecessary part ... as they say it is rubbish). And only 1-5 percent is occupied by the notorious genes that synthesize proteins.
Most of the information contained in chromosomes remains unknown to us. According to our scientists, DNA is the same text as the text of a book. But it has the ability to be readable not only letter by letter and line by line, but also from any letter, because there is no break between words. Reading this text with each subsequent letter, they get more and more new texts. You can also read in the opposite direction if the row is flat. And if a chain of text is deployed in three-dimensional space, as in a cube, then the text is readable in all directions.
The text is not stationary, it is constantly moving, changing, because our chromosomes breathe, sway, generating a huge amount of texts. Working with linguists and mathematicians of Moscow State University showed that the structure of human speech, book text and the structure of the DNA sequence are mathematically close, that is, these are really texts in languages that are still unknown to us. Cells talk to each other like you and me: the genetic apparatus has an infinite number of languages.
A person is a self-readable textual structure, cells talk to each other in the same way as people to each other - concludes Peter Petrovich Gariaev. Our chromosomes implement the program of building an organism from an egg through biological fields - photonic and acoustic. An electromagnetic image of the future organism is created inside the egg, its socioprogram is recorded, if you like - Fate.
This is another unexplored feature of the genetic apparatus, which is realized, in particular, with the help of one of the types of biofield - laser fields that can not only emit light, but also sound... Thus, the genetic apparatus manifests its potency through topographic memory.
Depending on what kind of light the holograms are illuminated with - and there are many of them, because many holograms can be recorded on one hologram - this or that image is obtained. Moreover, it can be read only in the same color with which it is written.
And our chromosomes emit a wide spectrum, from ultraviolet to infrared, and therefore can read multiple holograms from each other. As a result, a light and acoustic image of the future new organism appears, and in progression - all subsequent generations.
The program, which is written on DNA, could not have arisen as a result of Darwinian evolution: it takes time to write down such a huge amount of information, which is many times longer than the lifetime of the universe.
It's like trying to build a building for Moscow State University by throwing bricks. Genetic information can be transmitted at a distance; a DNA molecule can exist in the form of a field. A simple example of the transfer of genetic material is the penetration of viruses into our body, such as the Ebola virus.
This principle of "immaculate conception" can be used to create a kind of device that allows you to penetrate into the human body and influence it from the inside.
« We have developed, - says Petr Petrovich, - laser on DNA molecules. This thing is potentially formidable, like a scalpel: it can be healed, or it can be killed. Without exaggeration, I will say that it is basis for the creation of psychotropic weapons... The principle of operation is as follows.
The laser is based on simple atomic structures, and the DNA molecules are based on texts. You enter a certain text into a section of the chromosome, and these DNA molecules are converted into a laser state, that is, you act on them in such a way that the DNA molecules begin to glow and make a sound - to talk!
And at this moment, light and sound can penetrate into another person and introduce someone else's genetic program into him. And a person changes, he acquires other characteristics, begins to think and act in a different way. "
*****
The genetic code appears to have been invented outside the solar system several billion years ago.
This statement supports the idea of panspermia, the hypothesis that life was brought to Earth from outer space. This is, of course, a new and bold approach to the conquest of galaxies, if we imagine that this was a deliberate step of extraterrestrial super-beings who know how to operate with genetic material.
Researchers speculate that at some stage our DNA was encoded with an alien signal from an ancient extraterrestrial civilization. Scientists believe that the mathematical code in human DNA cannot be explained by evolution alone.
Galactic signature of humanity.
Surprisingly, it turns out that once the code has been installed, it will remain unchanged over cosmic time scales. As the researchers explain, our DNA is the most durable "material" and that is why the code is an extremely reliable and intelligent "signature" for those aliens who read it, says the Icarus magazine.
Experts say: “The written code can remain unchanged during cosmic time scales, in fact, this is the most reliable design. Therefore, it provides an extremely strong repository for smart signatures.... The genome, when appropriately rewritten with a new code with a signature, will be frozen in the cell and its offspring, which can then be carried through space and time. "
Researchers believe that human DNA is arranged in such a precise way that it reveals "a set of arithmetic and ideographic structures of a symbolic language." Scientists' work leads them to believe that we were literally “created outside the Earth” several billion years ago.
Universal language of the Universe - living cosmic codes
These ideas and beliefs are not accepted in the scientific community. However, these studies proved what some researchers have been saying for decades, that evolution could not have happened on its own, and that there is something extraterrestrial for our entire species.
However, these studies and statements do not reveal the main secret. A secret that remains as it is now; if extraterrestrial beings did create humanity and life on planet earth, then "who" or "what" created these extraterrestrial beings?
So we are a MESSAGE?
Humanity has been assigned the role of SMS with a view of the future ...
Source - http://oleg-bubnov.livejournal.com/233208.html
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The genetic code contains a reasonable signal
Scientists have discovered in the genetic code a number of purely mathematical and ideographic linguistic constructions that cannot be attributed to chance. This can only be interpreted as a reasonable signal.
In 2013, the results of a study were published, the authors of which tried to apply the method of searching for a signal from an extraterrestrial intelligent source (the SETI project) not to the vast expanses of the Universe ... but to the genetic code of terrestrial organisms.
“... We show that the terrestrial code exhibits high-precision ordering that satisfies the criteria for an information signal. Simple code structures reveal a harmonious whole of arithmetic and ideographic constructions of the same symbolic language. Accurate and systematic, these hidden constructs are presented as products of precise logic and non-trivial computations, and not the result of stochastic processes (the null hypothesis that this is the result of chance, together with supposed evolutionary mechanisms, is rejected with the meaning< 10-13). Конструкции настолько чётки, что кодовое отображение уникально выводится из своего алгебраического представления. Сигнал демонстрирует легко распознаваемые печати искусственности, среди которых символ нуля, привилегированный десятичный синтаксис и семантические симметрии. Кроме того, экстракция сигнала включает в себя логически прямолинейные, но вместе с тем абстрактные операции, что делает эти конструкции принципиально несводимыми к естественному происхождению. ...»
Thus, the genetic code is not only a code used to record information necessary for the construction and functioning of living organisms, but also a kind of "signature", the probability of accidental origin of which is less than 10-13. genetic code.
FSBEI HPE "Penza State University"
Pedagogical Institute named after V.G. Belinsky
Department of General Biology and Biochemistry
Course work
in the discipline "Biology"
on the topic "Coding and implementation of biological information in a cell, genetic code and its properties"
Penza 2014
Introduction
General properties of genetic material and levels of organization of the genetic apparatus
3. Properties of the gene
4.2 Ribonucleic acid
6. A method of recording genetic information in a DNA molecule. Biological code and its properties
6.2 Replication of a DNA molecule
6.4 Biosynthesis of protein in the cell
Conclusion
genetic deoxyribonucleic biosynthesis protein
Introduction
Primarily, all the diversity of life is determined by a variety of protein molecules that perform various biological functions in cells. The uniqueness of each cell lies in the uniqueness of its proteins. Cells that perform various functions, capable of synthesizing their own proteins using the information that is recorded in the DNA molecule.
Experiments on the transformation of bacteria were one of the proofs of the role of DNA in the transmission of hereditary information. F. Griffith (1928).
The second proof of the role of DNA in the transmission of hereditary information was obtained by N. Tsinder and J. Lederberg. In 1952, they described the phenomenon of transduction.
The evidence that nucleic acids, and not proteins, are carriers of genetic information, were the experiments of H. Frenkel-Konrath (1950). So with the discovery of the phenomena of transformation, transduction and the experiments of Frenkel-Konrath, rolnucleic acids were proved in the transmission of hereditary information.
In 1941 G. Beadle and E. Tatum established that genes are responsible for the formation of enzymes that, through cellular metabolism, affect the development of morphological and physiological characteristics.
In 1951, E. Chargaff discovered the phenomenon of complementary nitrogenous bases in the DNA molecule (Chargaff's rules), showing that the amount of adenine is always equal to the amount of thymine, and the amount of guanine is equal to the amount of cytosine.
In 1953, J. Watson, F. Crick and M. Wilkins proposed a model of the structure of the DNA molecule, which is a double helix.
Thus, in the early 50s it was proved that the material unit of heredity and variability is a gene that has a certain structural and functional organization. The primary functions of genes are storage and transmission of genetic information. The transfer of genetic information occurs from DNA to DNA during DNA replication. This way of transferring information from DNA to mRNA and protein F. Crick (1958) called - the central dogma of molecular biology.
In the 60s. by the works of M. Nirenberg, S. Ochoa, H. Korana and others, a complete deciphering of the genetic code was made, the correspondence of triplets of nucleotides in molecules of nucleic acids to certain amino acids was established.
In the 70s. methods of genetic engineering began to be actively developed, allowing purposefully change the hereditary properties of living organisms.
By the end of the 20th century, thanks to new molecular genetic technologies, it became possible to determine the nucleotide sequences in the DNA molecules of the genomes of various organisms (reading DNA texts). The DNA texts of the human genome, represented by a total of 3 billion base pairs, were mostly read by 2001. The scientific and practical direction of molecular biology, aimed at determining the nucleotide sequences of DNA molecules, is called genomics.
1. General properties of genetic material and levels of organization of the genetic apparatus
The elementary functional unit of the genetic apparatus, which determines the possibility of the development of an individual trait of a cell or an organism of a given species, is the -gene (hereditary deposit, according to G. Mendel). The transfer of genes in a series of generations of cells or organisms is achieved by material continuity - inheritance of parental traits by descendants. A trait is understood as a unit of morphological, physiological, biochemical, immunological, clinical and any other discreteness of organisms (cells), i.e. a separate quality or property by which they differ from each other.
Most of the above features of organisms or cells belong to the category of complex traits, the formation of which requires the synthesis of many substances, primarily proteins with specific properties of enzymes, immunoproteins, structural, contractile, transport and other proteins. The properties of a protein molecule are determined by the amino acid sequence of its polypeptide chain, which is directly specified by the sequence of nucleotides in the DNA of the corresponding gene and is an elementary, or simple, feature.
The main properties of a gene as a functional unit of the genetic apparatus are determined by its chemical organization.
2. Chemical organization of the gene
Studies aimed at elucidating the chemical nature of the hereditary material have irrefutably proved that the material substrate of heredity and variability are nucleic acids, which were discovered by F. Misher (1868) in the nuclei of pus cells. Nucleic acids are macromolecules, i.e. have a large molecular weight. These are polymers consisting of monomers-nucleotides, including the tricomponent: sugar (pentose), phosphate and nitrogenous base (purine or pyrimidine). A nitrogenous base (adenine, guanine, cytosine, thymine or uracil) is attached to the first carbon atom in the pentose C-1 molecule ", and phosphate is attached to the fifth carbon atom C-5" with the help of an ether bond; the third carbon atom C-3 "always has a hydroxyl group-OH. The connection of nucleotides into a nucleic acid macromolecule occurs by the interaction of the phosphate of one nucleotide with the hydroxyl of another so that a phosphodiester bond is established between them. As a result, a polynucleotide chain is formed. The backbone of the chain consists of alternating molecules of phosphate and sugar. One of the above nitrogenous bases is attached to the pentose molecules at position C-1 ". Assembly of the polynucleotide chain is carried out with the participation of the polymerase enzyme, which provides the attachment of the phosphate group of the next nucleotide to the hydroxyl group at position 3" of the previous nucleotide. chain occurs only at one end: where there is a free hydroxyl in position 3 ". The beginning of the chain always carries a phosphate group at the 5 "position. This allows the 5" and 3 "ends to be distinguished in it.
Among nucleic acids, two types of compounds are distinguished: deoxyribonucleic (DNA) and ribonucleic (RNA) acids. The study of the composition of the main carriers of hereditary material, chromosomes, revealed that their most chemically stable component is DNA, which is a substrate of heredity and variability.
3. Properties of the gene
Genes are characterized by certain properties: specificity, integrity and discreteness, stability and lability, pleiotropy, expressiveness and penetrance. The specificity of a gene is that each structural gene has only its own inherent order of nucleotide arrangement and determines the synthesis of a certain polypeptide, rRNA or tRNA. the fact that when programming the synthesis of a polypeptide, it acts as an indivisible unit, a change in which leads to a change in the polypeptide molecule. The gene as a functional unit is indivisible. The discreteness of a gene is determined by the presence of subunits in it. Currently, a pair of complementary nucleotides is considered the minimum structural subunit of a gene, and a codon is considered the minimum functional unit. Genes are relatively stable and rarely change (mutate). The frequency of spontaneous mutation of one gene is approximately 1 -10 -5 per generation.
The ability of a gene to change (mutate) is called lability. Genes, as a rule, have pleiotropic (multiple) effects, when one gene is responsible for the manifestation of several traits. This phenomenon, in particular, is observed in some enzymopathies, multiple congenital malformations, for example, in Marfan's syndrome.
4. Structure and function of DNA and RNA
The term nucleic acids was proposed by the German chemist R. Altmann in 1889 after these compounds were discovered in 1868. by the Swiss physician F. Mischer. He extracted the cells of purulent pneumococcus with dilute hydrochloric acid for several weeks and obtained an almost pure nuclear material in the remainder, calling it nuclein (from Latin nucleus - nucleus). Nucleic acids - DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
1 Deoxyribonucleic acid
DNA (deoxyribonucleic acid) molecules are the largest biopolymers; their monomer is a nucleotide. It consists of the remains of three substances: nitrogenous base, deoxyribose carbohydrate and phosphoric acid. There are four known nucleotides involved in the formation of the DNA molecule; they differ from each other in nitrogenous bases. Two nitrogenous bases, cytosine and thymine, are pyrimidine derivatives. Adenine and guanine are classified as purine derivatives. The name of each nucleotide reflects the name of the nitrogenous base. There are nucleotides: cytidyl (C), thymidyl (T), adenyl (A), guanyl (G). The connection of nucleotides in a DNA strand occurs through the carbohydrate of one nucleotide and the phosphoric acid residue of the neighboring one. According to the DNA model, both strands are twisted together around a common axis. The two strands of a molecule are held together by hydrogen bonds that arise between their complementary nitrogenous bases. Adenine is complementary to thymine, and guanine is complementary to cytosine. Between adenine and thymine there are two hydrogen bonds, between guanine and cytosine there are three.
DNA is located in the nucleus, where it, together with proteins, forms linear structures - chromosomes. Chromosomes are clearly visible during microscopy during the period of nuclear division; in the interphase they are despiralized.
DNA is found in mitochondria and plastids (chloroplasts and leukoplasts), where their molecules form circular structures. Circular DNA is also present in the cells of prenuclear organisms.
DNA is capable of self-duplication (reduplication). This takes place at a certain period of the cell's life cycle, called synthetic. Reduplication allows maintaining the constancy of the DNA structure. If, under the influence of various factors in the process of replication in the DNA molecule, changes occur in the number, in the sequence of nucleotides, then mutations occur.
The main function of DNA is the storage of hereditary information contained in the sequence of nucleotides that form its molecule, and the transfer of this information to daughter cells. The ability to transfer hereditary information from cell to cell is ensured by the ability of chromosomes to divide into chromatids with subsequent reduplication of the DNA molecule. DNA contains all the information about the structure and activity of cells, the characteristics of each cell and the organism as a whole. This information is called genetic. The DNA molecule encodes the genetic information of the sequence of amino acids in a protein molecule. The transfer and implementation of information is carried out in the cell with the participation of ribonucleic acids.
2 Ribonucleic acid
Ribonucleic acids are of several types. There is ribosomal, transport and messenger RNA. The RNA nucleotide consists of one of the nitrogenous bases (adenine, guanine, cytosine and uracil), a carbohydrate - ribose, and a phosphoric acid residue. RNA molecules are single-stranded.
Ribosomal RNA (r-RNA) in conjunction with a protein is part of ribosomes. R-RNA makes up 80% of all RNA in the cell. Protein is synthesized on ribosomes. Informational RNA (i-RNA) makes up from 1 to 10% of the total RNA in the cell. In structure, i-RNA is complementary to the part of the DNA molecule that carries information about the synthesis of a certain protein. The length of i-RNA depends on the length of the DNA segment from which the information was read. I-RNA transfers information about protein synthesis from the nucleus to the cytoplasm.
Transport RNA (t-RNA) makes up about 10% of all RNA. It has a short chain of nucleotides and is found in the cytoplasm. T-RNA attaches certain amino acids and brings them to the site of protein synthesis to the ribosomes. T-RNA has a trefoil shape. At one end there is a nucleotide triplet (anticodon) that encodes a specific amino acid. At the other end there is a triplet of nucleotides, to which an amino acid is attached. When the t-RNA triplet (anticodon) and the i-RNA triplet (codon) are complementary, the amino acid occupies a certain place in the protein molecule.
RNA is found in the nucleolus, in the cytoplasm, in the ribosomes, in the mitochondria and in the plastids.
There is another type of RNA in nature. This is viral RNA. For some viruses, it performs the function of storing and transmitting hereditary information. In other viruses, viral DNA performs this function.
5. Evidence for a genetic role for nucleic acids
The experiments of Frederick Griffith 1928 The bacterium Pneutnococcus pneumoniae is known to have several forms. The virulence of bacteria is determined by the presence of a mucopolysaccharide capsule located on the cell surface. This capsule protects the bacterium from the effects of the host organism. As a result, the multiplied bacteria kill the infected animal. The bacteria of this strain (S-strain) form smooth colonies. Avirulent forms of bacteria do not have a protective capsule and form rough colonies (R-strain). Microbiologist Frederick Griffiths injected live pneumococcal R-strain together with S-strain killed by high temperature (65 ° C) in 1928 in mice. After some time, he managed to isolate live pneumococci with a capsule from infected mice. Thus, it turned out that the property of the killed pneumococcus - the ability to form a capsule - passed to a living bacterium, i.e. there was a transformation. Since the sign of the presence of a capsule is hereditary, it should have been assumed that some part of the hereditary substance from the bacteria of the S strain passed to the cells of the R.
In 1944, O.T. Avery, K.M. McLeod and M. McCarthy showed that the same transformation of pneumococcal types can occur in a test tube, i.e. invitro. These researchers established the existence of a special substance - the "transforming principle" - an extract from the cells of the S strain, enriched with DNA. As it turned out further, DNA isolated from the S-strain cells and added to the R-strain culture transformed part of the cells into the S-form. The cells steadily passed on this property during further reproduction. Treatment of the "transforming factor" with DNase, an enzyme that degrades DNA, blocked transformation. These data showed for the first time that it was DNA, and not protein, as it was believed until then, to be hereditary material.
d. An experiment by Alfred Hershey and Martha Chase. As you know, the T2 phage is a virus that infects the bacterium E. coli. phage particles are absorbed on the outer surface of the cell, their material penetrates inside and after about 20 minutes the bacterium is lysed, releasing a large number of phage particles - offspring. In 1952, Alfred Hershey and Martha Chase infected bacteria with T2 phages, which were labeled with radioactive compounds: DNA with 32P. The protein part of the phage is 35S. After infection of bacteria with phages, using centrifugation it was possible to isolate two fractions: empty protein membranes of the phage and bacteria infected with phage DNA. It turned out that 80% of the 35S label remained in empty phage membranes, and 70% of the 32P label remained in infected bacteria. The progeny phages received only about 1% of the original protein labeled with 35S, but they also found about 30% of the 32P label. The results of this experiment directly showed that the DNA of the parental phages penetrates the bacteria and then becomes a component of the developed new phage particles.
d. Experiments of Frenkel - Konrat Frenkel-Konrat worked with the tobacco mosaic virus (TMV). This virus contains RNA, not DNA. It was known that different strains of the virus cause different patterns of damage to tobacco leaves. After changing the protein coat, the "disguised" viruses caused a lesion pattern characteristic of the strain whose RNA was coated with a foreign protein.
Consequently, not only DNA, but also RNA can serve as a carrier of genetic information. Today, there are hundreds of thousands of proofs of the genetic role of nucleic acids. These three are classic.
6. A method of recording genetic information in a DNA molecule. Biological code and its properties
1 Packaging levels of genetic material
The double helix of the DNA molecule combines with histone and histone proteins, forming nucleoprotein fibrils. The length of these fibrils in the diploid set of human chromosomes is about 2 m, and the total length of all chromosomes in the metaphase is about 150 μm. It is generally accepted that each chromatid of a chromosome contains one continuous DNA molecule. Packing of genetic material is achieved by spiraling (condensation) of fibrils.
The first level of packaging is DNA-nucleosomal. The nucleosome is a cylinder (octamer) 11 nm in diameter and 6 nm in height, containing two molecules of each of the four histones (H2A, H2B, H3, H4), around which the DNA double helix forms about two turns and passes to the next cylinder. The length of the wound DNA fragment is about 60 nm (about 200 base pairs). The nucleosome strand thus formed has a diameter of about 13 nm. The length of the DNA molecule decreases by 5-7 times. The nucleosomal level of packaging is detected in an electron microscope at interphase and during mitosis.
The second level of packing is solenoid (supernucleosomal). The nucleosomal strand condenses, its nucleosomes are stitched together. histone HI and is formed by a helix with a diameter of about 25 nm. One turn of the helix contains 6-10 nucleosomes. This achieves a 6-fold shortening of the thread. The supernucleosomal level of packing is found in an electron microscope in both interphase and mitotic chromosomes.
The third level of packing is chromatid (loop). The supernucleosomal filament coils with the formation of loops and bends. It forms the basis of the chromatid and provides the chromatid level of packing. It shows up in prophase. The diameter of the loops is about 50 nm. The DNP (DNA + protein) strand is shortened 10-20 times.
The fourth level of packing is the level of the metaphase chromosome. Chromatids in metaphase are still capable of spiralizing with the formation of euchromatin (weakly spiralized) and heterochromatin (strongly spiralized) regions; there is a 20-fold shortening. Metaphase chromosomes have a length of 0.2 to 150 µm and a diameter of 0.2 to 5.0 µm. The overall result of condensation is a 10,000-fold shortening of the DNA strand.
Chromosomes of prokaryotic cells are circular DNA molecules containing about 5-106 base pairs and forming complexes with non-histone proteins. Using special methods of destruction of prokaryotes, it is possible to find that their DNA is assembled into beads that are close in size to the nucleosomes of eukaryotes. These beads are very labile, indicating little interaction between DNA and proteins.
The nature of the condensation of the chromosome of prokaryotes is not fully elucidated, but in general it can be isolated in the form of a compact structure called a nucleoid. Prokaryotic cells (bacteria) also contain circular double-stranded DNA molecules, consisting of several thousand base pairs, which they can exchange with other bacteria. These autonomous genetic plasmid elements are capable of replicating independently of nucleoid replication. Most plasmids contain genes for resistance to antibacterial factors. Ring-shaped DNA molecules are also found in eukaryotic cells in self-replicating organelles (mitochondria, plastids). These molecules are small and encode a small number of proteins required for the autonomous functions of organelles. Organoid DNA is not associated with histones.
6.2 Replication of a DNA molecule
Replication of DNA molecules occurs during the synthetic period of the interphase. Each of the two chains of the parent molecule serves as a template for the synthesis of a new chain according to the principle of complementarity. After replication, the DNA molecule contains one maternal chain and one daughter, newly synthesized (DNA synthesis is semi-conserved). Since two complementary strands in the DNA molecule are directed in opposite directions, and DNA polymerase can move along the matrix chains only from the 5 "end to the 3" end, the synthesis of new strands is antiparallel (antiparallel principle). so that the old molecule is uncoiled and stretched. But the simultaneous unwinding of spirals consisting of a huge number of nucleotide pairs (several million) is impossible. Therefore, replication begins at several places in the DNA molecule. The section of a DNA molecule from the point of origin of one replication to the point of origin of another is called a replicon. The bacterial chromosome contains one replicon. The eukaryotic chromosome contains many replicons, in which the duplication of the DNA molecule occurs simultaneously. The replicon necessarily has controlling elements: the start point at which replication is initiated, and the end point at which replication stops. The place where replication takes place is called the replication fork. The replication fork moves along the DNA molecule from its starting point (starting point) to its ending point. Since DNA polymerase can only move in one direction (5 "-3"), in each replication fork it can gradually and continuously build only one new strand of the DNA molecule. Another daughter DNA molecule is synthesized in separate short sections of 150-200 nucleotides (Okazaki fragments) under the action of DNA polymerase moving in the opposite direction. These short sections of the newly synthesized polynucleotide chain of one replicon are linked together by an enzyme ligase. This principle of synthesis of new DNA strands is called intermittent. Plots of subsidiaries. DNA molecules synthesized in neighboring replicons are also ligated by the enzyme ligase. The entire genome of a cell is replicated only once during a period of time corresponding to one mitotic cycle.
6.3 Genetic code and its properties
The structure of proteins is determined by the set and order of arrangement of amino acids in their peptide chains. It is this sequence of amino acids in peptides that is encoded in DNA molecules using a biological (genetic) code. The relative primitiveness of the DNA structure, representing the alternation of only four different nucleotides, for a long time prevented researchers from considering this compound as a material substrate of heredity and variability, in which extremely diverse information must be encrypted.
Complete deciphering of the genetic code was carried out in the 60s. our century. Of the 64 possible DNA triplets, 61 code for various amino acids; the remaining 3 are called meaningless, or nonsense triplets. They do not encrypt amino acids and serve as punctuation marks when reading investigative information. These include ATT, ATTs, ATTs. Attention is drawn to the obvious redundancy of the code, which manifests itself in the fact that many amino acids are encrypted with several triplets. This property of the triplet code, called degeneracy, is very important, since the appearance in the structure of the DNA molecule of changes by the type of replacement of one nucleotide in the polynucleotide chain may not change the meaning of the triplet. The resulting new combination of three nucleotides encodes the same amino acid.
In the process of studying the properties of the genetic code, its specificity was discovered. Each triplet is able to encode only one specific amino acid. An interesting fact is the complete correspondence of the code in various types of living organisms. This universality of the genetic code testifies to the unity of the origin of the entire variety of living forms on Earth in the process of biological evolution. Minor differences in the genetic code are found in the DNA of mitochondria of some species. This does not contradict the general statement about the universality of the code, but testifies in favor of a certain divergence of its evolution in the early stages of life.
Deciphering the code in the DNA mitochondria of various species showed that in all cases, a common feature is noted in mitochondrial DNA: the ACT triplet is read as ACC, and therefore from a nonsense triplet it turns into a tryptophan amino acid code. are its continuity and non-overlapping codons during reading. This means that the sequence of nucleotides is read triplet by triplet without gaps, while adjacent triplets do not overlap, i.e. each individual nucleotide is included in only one triplet at a given reading frame. The proof of the non-overlapping of the genetic code is the replacement of only one amino acid in the peptide while replacing one nucleotide in the DNA. If a nucleotide is included in several overlapping triplets, its replacement would entail the replacement of 2–3 amino acids in the peptide chain.
Thus, the genetic code is not a random conglomerate of correspondences between codons and amino acids, but a highly organized system of correspondences supported by complex molecular mechanisms.
4 Biosynthesis of protein in the cell
The mediator in the transfer of genetic information (nucleotide order) from DNA to protein is mRNA (informational RNA). It is synthesized in the nucleus by one of the DNA strands according to the principle of complementarity after the rupture of hydrogen bonds between the two strands (RNA polymerase enzyme). The process of rewriting information from DNA to mRNA is called transcription. The mRNA synthesized in this way (matrix synthesis) is released through the pores of the nucleus into the cytoplasm and interacts with a small subunit of one or more ribosomes. Ribosomes united by one mRNA molecule are called polysomes. The same protein molecules are synthesized on each ribosome of the polysome.
The next step in protein biosynthesis is translation, translation of the nucleotide sequence in the mRNA molecule into the amino acid sequence in the polypeptide chain. Transport RNAs (tRNAs) bring amino acids to the ribosome. The tRNA molecule is similar in configuration to a clover leaf and has two active centers. At one end of the molecule there is a triplet of free nucleotides, which is called an anticodon and corresponds to a specific amino acid. Since many amino acids are encoded by several triplets, the number of different tRNAs is much more than 20 (60 identified). The second active site is the site opposite to the anticodon, to which the amino acid is attached. At the 5 "end of the tRNA molecule there is always guanine, and at the 3" end of the CCA molecule. Each amino acid binds to one of its specific tRNAs with the participation of a special form of the enzyme aminoacyl-tRNA synthetase and ATP. As a result, a complex of the amino acid stRNA-aminoacyl-tRNA is formed, in which the binding energy between the terminal nucleotide A (in the CCA triplet) and the amino acid is sufficient for the formation of a peptide bond in the future. Amino acids are transported to the large ribosome subunit. At any given moment, there are two codons and RNA inside the ribosome: one is on the antitaminoacyl center, the second is opposite the peptidyl center. If the anticodon of tRNA and the codonaminoacyl center are complementary, then the tRNAi amino acid is transferred to the peptidyl center (the ribosome moves one triplet), the amino acid is detached from the tRNA and attaches to the previous amino acid, and the tRNA leaves the ribosome for the next amino acid. The same happens with the second tRNA and its amino acid. Thus, the polypeptide molecule is assembled in full accordance with the information recorded on the mRNA. In the process of translation, there are three stages: initiation, elongation and termination. Initiation (beginning of translation) consists in binding of the ribosome of sRNA, for which there is a special initiation codon (AUG) at the beginning of the mRNA molecule and a specific sequence of nucleotides that is responsible for binding to the ribosome. Elongation (translation process) includes reactions from the formation of the first peptide bond to the attachment of the last amino acid to the polypeptide molecule. At this time, the ribosome moves from the first to the last codon to the mRNA. Termination (end of translation) is due to the presence of termination codons (UAA, UAH, U GA), which stop protein synthesis; there is a separation of the ribosome from the mRNA. The regulation of protein synthesis in eukaryotes can be carried out at the level of transcription and translation. The regulatory function is performed by chromosomal proteins (histones). Their molecules are positively charged and easily bind to negatively charged phosphates, influencing the transcription of certain genes using DNA-dependent RNA polymerase. Modifications of histones (phosphorylation, acetylation, methylation) weaken their bond with DNA and facilitate transcription. Acid non-histone proteins, by binding to certain regions of DNA, also facilitate transcription. They also regulate transcription and low molecular weight nuclear RNAs, which are in a complex with proteins and can selectively turn on genes. Various anabolic steroids, insulin, precursors of nucleotides and nucleic acids (inosine, potassium orotate) enhance protein synthesis. Protein synthesis inhibitors are antibiotics (rifamycins, olivomycin), some antineoplastic drugs (vinblastine, vincristine, 5-fluorouracil), modified nitrogenous bases and nucleosides.
In the laboratory, protein synthesis takes a lot of time, effort and money. In the cell, the synthesis of protein molecules consisting of hundreds or more amino acids is carried out within a few seconds. This is primarily due to the matrix principle of the synthesis of nucleic acids and proteins, which ensures the exact sequence of monomer units in the synthesized polymers. If such reactions occurred as a result of a random collision of molecules, they would proceed infinitely slowly. Enzymes have a significant effect on the speed and accuracy of all protein synthesis reactions. With the participation of special enzymes, the synthesis of DNA, i-RNA, the combination of amino acids with tRNA, etc. takes place. The process of protein synthesis also requires a lot of energy. Thus, the combination of each amino acid with t-RNA consumes the energy of one ATP molecule. You can imagine how many ATP molecules are cleaved during the synthesis of a medium-sized protein consisting of several hundred amino acids.
Conclusion
The biological properties of living matter are determined by the combined properties of its constituent bioorganic matter, chemical energy and molecular information. In this regard, living matter obeys not only all known physical and chemical laws, but also informational laws. It is clear that bioorganic matter is the material basis for the construction of any living system. In addition, biological macromolecules and structures also act as a carrier of molecular information; therefore, information in the structure of a living thing has a chemical recording form. Thanks to the processing and circulation of hereditary information in the process of life, the control and regulation of biochemical and molecular processes is carried out, the entropy (disorganization) of the living system is reduced. Only information resources and regularities allow matter, energy and information in a living system to circulate, renew, reproduce and create new biological realities. Self-government and information exchange are the most essential characteristics of the functioning of living systems. Therefore, in any living cells, the phenomena of coding, storage, recoding, transmission, processing and use of genetic information are key for all biological processes.
Based on the achievements of molecular biology, biochemistry and genetics, a new direction in genetics, genetic engineering, has been intensively developing in recent decades, the purpose of which is to construct genetic structures according to a predetermined plan, to create organisms with a new genetic program by transferring genetic information from one organism to another.
Genetic engineering dates back to 1973, when geneticists Stanley Cohen and Herbert Boyer introduced a new gene into E. coli bacteria.
Since 1982, firms in the USA, Japan, Great Britain and other countries have been producing genetically engineered insulin. The cloned human insulin genes were introduced into the bacterial cell, where the synthesis of a hormone began, which natural microbial strains never synthesized.
About 200 new diagnostic drugs have already been introduced into medical practice, and more than 100 genetically engineered drugs are at the stage of clinical study. Among them are drugs that cure arthrosis, cardiovascular diseases, some tumor processes and, possibly, even AIDS. Among several hundreds of genetic engineering firms, 60% work on the production of pharmaceuticals and diagnostic products.
In 1990, the Human Genome Project was launched in the United States, the goal of which was to determine the entire genetic year of a person. The project, in which Russian geneticists also played an important role, was completed in 2003. As a result of the project, 99% of the genome was determined with an accuracy of 99.99% (1 error per 10,000 nucleotides). The completion of the project has already yielded practical results, such as easy-to-use tests that can determine genetic predisposition to many hereditary diseases.
Since the 1990s, hundreds of laboratories have been researching the use of gene therapy to treat disease. We now know that gene therapy can treat diabetes, anemia, certain cancers, Huntington's disease, and even cleanse arteries. More than 500 clinical trials of various types of gene therapy are underway.
The unfavorable environmental situation and a number of other similar reasons lead to the fact that more and more children are born with serious hereditary defects. Currently, 4000 hereditary diseases are known, for most of which no effective treatment has been found.
Today it is possible to diagnose many genetic diseases at the stage of the embryo or embryo. So far, it is only possible to terminate pregnancy at a very early stage in the event of serious genetic defects, but it will soon become possible to correct the genetic code by correcting and optimizing the genotype of the unborn child. This will completely avoid genetic diseases and improve the physical, mental and mental characteristics of children.
Based on the foregoing, there are convincing grounds to believe that the general laws and principles of information coding have become not only the fundamental foundations of Life, but, subsequently, have been rediscovered by man and found widespread in many areas of human activity.
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In any cell and organism, all the features of the anatomical, morphological and functional nature are determined by the structure of the proteins that are included in them. The hereditary property of the body is the ability to synthesize certain proteins. The amino acids are located in the polypeptide chain, on which biological traits depend.
Each cell is characterized by its own sequence of nucleotides in the polynucleotide DNA chain. This is the genetic code of DNA. Through it, information about the synthesis of certain proteins is recorded. This article describes what the genetic code is, its properties and genetic information.
A bit of history
The idea that the genetic code may exist was formulated by J. Gamow and A. Down in the middle of the twentieth century. They described that the nucleotide sequence responsible for the synthesis of a particular amino acid contains at least three units. Later, they proved the exact number of three nucleotides (this is a unit of the genetic code), which was called a triplet or codon. There are sixty-four nucleotides in total, because the acid molecule, where RNA occurs, consists of residues of four different nucleotides.
What is the genetic code
The way of coding the protein amino acid sequence due to the nucleotide sequence is characteristic of all living cells and organisms. This is what the genetic code is.
There are four nucleotides in DNA:
- adenine - A;
- guanine - G;
- cytosine - C;
- thymine - T.
They are designated by capital letters in Latin or (in Russian-language literature) Russian.
There are also four nucleotides in RNA, but one of them differs from DNA:
- adenine - A;
- guanine - G;
- cytosine - C;
- uracil - U.
All nucleotides line up in chains, and a double helix is obtained in DNA, and a single helix in RNA.
Proteins are built on where they are located in a certain sequence, determine its biological properties.
Properties of the genetic code
Tripletness. The unit of the genetic code consists of three letters, it is triplet. This means that the twenty existing amino acids are encoded in three specific nucleotides called codons or trilpets. There are sixty-four combinations that can be made from four nucleotides. This amount is more than enough to encode twenty amino acids.
Degeneracy. Each amino acid corresponds to more than one codon, with the exception of methionine and tryptophan.
Unambiguity. One codon encrypts one amino acid. For example, in the gene of a healthy person with information about the beta target of hemoglobin, the triplet GAG and GAA encodes A in everyone with sickle cell anemia, one nucleotide is replaced.
Collinearity. The amino acid sequence always matches the nucleotide sequence that the gene contains.
The genetic code is continuous and compact, which means that it does not have "punctuation marks". That is, starting at a certain codon, there is a continuous reading. For example, AUGGUGTSUUAAUGUG will be read as: AUG, GUG, TSUU, AAU, GUG. But not AUG, UGG and so on or in any other way.
Versatility. It is the same for absolutely all terrestrial organisms, from humans to fish, fungi and bacteria.
table
Not all available amino acids are present in the table shown. Hydroxyproline, hydroxylysine, phosphoserine, iodine derivatives of tyrosine, cystine and some others are absent, since they are derivatives of other amino acids encoded by mRNA and formed after protein modification as a result of translation.
It is known from the properties of the genetic code that one codon is capable of encoding one amino acid. The exception is the genetic code, which performs additional functions and encodes valine and methionine. IRNA, being at the beginning with a codon, attaches t-RNA, which carries formylmethion. Upon completion of the synthesis, it is cleaved off by itself and captures the formyl residue, being converted into the methionine residue. Thus, the aforementioned codons are initiators of the synthesis of the polypeptide chain. If they are not at the beginning, then they are no different from others.
Genetic information
This concept refers to a property program that is passed down from ancestors. It is embedded in heredity as a genetic code.
The genetic code is implemented during protein synthesis:
- informational i-RNA;
- ribosomal r-RNA.
Information is transmitted by direct communication (DNA-RNA-protein) and reverse (environment-protein-DNA).
Organisms can receive, store, transmit it and use it in the most efficient way.
Passed by inheritance, information determines the development of an organism. But due to interaction with the environment, the reaction of the latter is distorted, due to which evolution and development occurs. Thus, new information is put into the body.
The calculation of the laws of molecular biology and the discovery of the genetic code illustrated that it is necessary to combine genetics with Darwin's theory, on the basis of which a synthetic theory of evolution - non-classical biology - appeared.
Darwin's heredity, variability, and natural selection are complemented by genetically determined selection. Evolution is realized at the genetic level through random mutations and the inheritance of the most valuable traits that are most adapted to the environment.
Decoding the code in a person
In the nineties, the Human Genome project was launched, as a result of which fragments of the genome containing 99.99% of human genes were discovered in the 2000s. Fragments that are not involved in protein synthesis and are not encoded remain unknown. Their role is still unknown.
The last chromosome 1 discovered in 2006 is the longest in the genome. More than three hundred and fifty diseases, including cancer, appear as a result of disorders and mutations in it.
The role of such studies can hardly be overestimated. When they discovered what the genetic code is, it became known by what patterns the development takes place, how the morphological structure, psyche, predisposition to certain diseases, metabolism and vices of individuals are formed.