Transcription- the process of RNA synthesis using DNA as a template, occurring in all living cells. In other words, it is the transfer of genetic information from DNA to RNA.
During gene transcription, the biosynthesis of RNA molecules complementary to one of the template DNA strands occurs, accompanied by the polymerization of four ribonucleoside triphosphates (ATP, GTP, CTP and UTP) with the formation of 3"–5" phosphodiester bonds and the release of inorganic pyrophosphate.
Transcription is catalyzed by an 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"
RNA polymerases can consist of one or more subunits. In mitochondria and some bacteriophages, for example SP6, T7, with a small number of genes in simple genomes, where there is no complex regulation, the RNA polymerase consists of a single subunit. For bacteria and eukaryotes, with a large number of genes and complex regulatory systems, RNA polymerases are composed of several subunits. It has been shown that phage RNA polymerases consisting of one subunit can interact with bacterial proteins, which change their properties [Patrushev, 2000].
In prokaryotes, the synthesis of all types of RNA is carried out by the same enzyme.
Eukaryotes have 3 nuclear RNA polymerases, mitochondrial RNA polymerases, and chloroplast RNA polymerases.
Ribonucleoside triphosphates (activated nucleotides) serve as substrates for RNA polymerases. The entire transcription process is carried out due to the energy of high-energy bonds of activated nucleotides.

The first nucleotide in RNA is always purine in the form of triphosphate.
Transcription factors- proteins that interact with each other, regulatory regions of DNA and RNA polymerase to form a transcription complex and regulate transcription. Thanks to transcription factors and gene regulatory sequences, specific RNA synthesis becomes possible.
Principles of Transcription
complementarity - mRNA is complementary to the DNA template strand and is similar to the DNA coding strand
antiparallelism
unipolarity
primerless - RNA polymerase does not require a primer
asymmetry
Transcription stages

1. promoter recognition and tying- RNA polymerase binds to the TATA box of the 3’ promoter with the help of basic transcription factors, additional factors inhibit or stimulate attachment
2. initiation- formation of the first phosphodiester bond between Pu and the first nucleotide. A nucleotide complementary to the second DNA nucleotide is added to purine triphosphate with the cleavage of pyrophosphate from the nucleoside triphosphate forming a diester bond
3. elongation(3’→5’) - mRNA homologous to non-template (coding, sense) DNA, synthesized on template DNA; which of the two DNA strands will be the template is determined by the direction of the promoter
4. termination

Transcription factories

There is a number of experimental data indicating that transcription occurs in the so-called transcription factories: huge, according to some estimates, up to 10 MDa complexes that contain about 8 RNA polymerases II and components for subsequent processing and splicing, as well as proof-reading of newly synthesized transcript. In the cell nucleus, there is a constant exchange between pools of soluble and activated RNA polymerase. Active RNA polymerase is involved in such a complex, which in turn is a structural unit that organizes chromatin compaction. Latest data. indicate that transcription factories exist even in the absence of transcription, they are fixed in the cell (it is not yet clear whether they interact with the cell matrix or not) and represent an independent nuclear subcompartment. Attempts to isolate the protein functional complex of the transcription factory have not yet led to success due to its huge size and low solubility.

Transcription in biology is a multi-stage process of reading information from DNA, which is a component of Nucleic acid is the carrier of genetic information in the body, so it is important to correctly decipher it and transfer it to other cellular structures for further assembly of peptides.

Definition of "transcription in biology"

Protein synthesis is the main vital process in any cell of the body. Without the creation of peptide molecules, it is impossible to maintain normal life functions, since these organic compounds are involved in all metabolic processes, are structural components of many tissues and organs, and play signaling, regulatory and protective roles in the body.

The process that begins protein biosynthesis is transcription. Biology briefly divides it into three stages:

1. Initiation.
2. Elongation (growth of RNA chain).
3. Termination.

Transcription in biology is a whole cascade of step-by-step reactions, as a result of which RNA molecules are synthesized on a DNA matrix. Moreover, in this way not only informational ribonucleic acids are formed, but also transport, ribosomal, small nuclear and others.

Like any biochemical process, transcription depends on many factors. First of all, these are enzymes that differ between prokaryotes and eukaryotes. These specialized proteins help initiate and carry out transcription reactions accurately, which is important for high-quality protein output.

Transcription of prokaryotes

Since transcription in biology is the synthesis of RNA on a DNA template, the main enzyme in this process is DNA-dependent RNA polymerase. In bacteria there is only one type of such polymerases for all molecules

RNA polymerase, according to the principle of complementarity, completes the RNA chain using the DNA template strand. This enzyme contains two β-subunits, one α-subunit and one σ-subunit. The first two components perform the function of forming the enzyme body, and the remaining two are responsible for retaining the enzyme on the DNA molecule and recognizing the promoter part of deoxyribonucleic acid, respectively.

By the way, the sigma factor is one of the signs by which a particular gene is recognized. For example, the Latin letter σ with the subscript N means that this RNA polymerase recognizes genes that are turned on when there is a lack of nitrogen in the environment.

Transcription in eukaryotes

Unlike bacteria, transcription in animals and plants is somewhat more complex. Firstly, each cell contains not one, but three types of different RNA polymerases. Among them:

1. RNA polymerase I. It is responsible for the transcription of ribosomal RNA genes (with the exception of 5S RNA ribosomal subunits).
2. RNA polymerase II. Its task is to synthesize normal information (template) ribonucleic acids, which subsequently participate in translation.
3. RNA polymerase III. The function of this type of polymerase is to synthesize 5S-ribosomal RNA.

Secondly, for promoter recognition in eukaryotic cells it is not enough to have only a polymerase. Special peptides called TF proteins also participate in the initiation of transcription. Only with their help can RNA polymerase land on DNA and begin the synthesis of a ribonucleic acid molecule.

Transcription meaning

The RNA molecule, which is formed on the DNA template, subsequently attaches to ribosomes, where information is read from it and protein is synthesized. The process of peptide formation is very important for the cell, because Without these organic compounds, normal life activity is impossible: they are primarily the basis for the most important enzymes of all biochemical reactions.

Transcription in biology is also a source of rRNA, which as well as tRNA, which are involved in the transfer of amino acids during translation to these non-membrane structures. SnRNAs (small nuclear ones) can also be synthesized, the function of which is to splice all RNA molecules.

Conclusion

Translation and transcription in biology play an extremely important role in the synthesis of protein molecules. These processes are the main component of the central dogma of molecular biology, which states that RNA is synthesized on the DNA matrix, and RNA, in turn, is the basis for the beginning of the formation of protein molecules.

Without transcription, it would be impossible to read the information that is encoded in deoxyribonucleic acid triplets. This once again proves the importance of the process at the biological level. Any cell, be it prokaryotic or eukaryotic, must constantly synthesize new and new protein molecules that are currently needed to maintain life. Therefore, transcription in biology is the main stage in the work of each individual cell of the body.

Life in carbon form exists due to the presence of protein molecules. And protein biosynthesis in the cell is the only possibility for gene expression. But to implement this process, it is necessary to launch a number of processes associated with the “unpacking” of genetic information, searching for the desired gene, reading it and reproducing it. The term “transcription” in biology specifically refers to the process of transferring information from a gene to messenger RNA. This is the start of biosynthesis, that is, the direct implementation of genetic information.

Storage of genetic information

In the cells of living organisms, genetic information is localized in the nucleus, mitochondria, chloroplasts and plasmids. Mitochondria and chloroplasts contain a small amount of animal and plant DNA, while bacterial plasmids are the storage site for genes responsible for rapid adaptation to environmental conditions.

In viral bodies, hereditary information is also stored in the form of RNA or DNA polymers. But the process of its implementation is also associated with the need for transcription. In biology, this process is of exceptional importance, since it is it that leads to the implementation of hereditary information, triggering protein biosynthesis.

In animal cells, hereditary information is represented by a polymer of DNA, which is compactly packaged inside the nucleus. Therefore, before protein synthesis or reading of any gene, certain stages must pass: unwinding of condensed chromatin and “release” of the desired gene, its recognition by enzyme molecules, transcription.

In biology and biological chemistry, these stages have already been studied. They lead to the synthesis of a protein, the primary structure of which was encoded in a single gene.

Transcription pattern in eukaryotic cells

Although transcription in biology has not been sufficiently studied, its sequence is traditionally presented in the form of a diagram. It consists of initiation, elongation and termination. This means that the entire process is divided into three component phenomena.

Initiation is a set of biological and biochemical processes that lead to the beginning of transcription. The essence of elongation is the continued growth of the molecular chain. Termination is a set of processes that lead to the cessation of RNA synthesis. By the way, in the context of protein biosynthesis, the process of transcription in biology is usually identified with the synthesis of messenger RNA. Based on it, a polypeptide chain will later be synthesized.

Initiation

Initiation is the least understood transcription mechanism in biology. What it is from a biochemical point of view is unknown. That is, the specific enzymes responsible for triggering transcription are not recognized at all. Also unknown are the intracellular signals and the methods of their transmission, which indicate the need for the synthesis of a new protein. This is a fundamental task for cytology and biochemistry.

Elongation

It is not yet possible to separate the process of initiation and elongation in time due to the impossibility of conducting laboratory studies designed to confirm the presence of specific enzymes and trigger factors. Therefore, this border is very conditional. The essence of the elongation process comes down to lengthening the growing chain, synthesized on the basis of the DNA template section.

It is believed that elongation begins after the first translocation of RNA polymerase and the beginning of the attachment of the first kadon to the starting site of RNA. During elongation, cadons are read in the direction of the 3"-5" strand on a despiralized DNA section divided into two strands. At the same time, the growing RNA chain is added with new nucleotides complementary to the template DNA region. In this case, the DNA is “expanded” to a width of 12 nucleotides, that is, 4 kadons.

The enzyme RNA polymerase moves along the growing chain, and “behind” it the DNA is reversely “cross-linked” into a double-stranded structure with the restoration of hydrogen bonds between nucleotides. This partly answers the question of what process is called transcription in biology. It is elongation that is the main phase of transcription, because during its course the so-called intermediary between the gene and protein synthesis is assembled.

Termination

The process of transcription termination in eukaryotic cells is poorly understood. So far, scientists have reduced its essence to stopping DNA reading at the 5" end and attaching a group of adenine bases to the 3" end of RNA. The latter process allows the chemical structure of the resulting RNA to be stabilized. There are two types of termination in bacterial cells. It is a Rho-dependent and Rho-independent process.

The first occurs in the presence of the Rho protein and is reduced to a simple breaking of hydrogen bonds between the template region of DNA and the synthesized RNA. The second, Rho-independent, occurs after the appearance of the stem-loop if there is a set of uracil bases behind it. This combination causes the RNA to detach from the DNA template. It is obvious that transcription termination is an enzymatic process, but specific biocatalysts for it have not yet been found.

Viral transcription

Viral bodies do not have their own protein biosynthesis system, and therefore cannot reproduce without exploiting cells. But viruses have their own genetic material, which needs to be realized and also integrated into the genes of infected cells. To do this, they have a number of enzymes (or exploit cell enzyme systems) that transcribe their nucleic acid. That is, this enzyme, based on the genetic information of the virus, synthesizes an analogue of messenger RNA. But it is not RNA at all, but a DNA polymer, complementary to, for example, human genes.

This completely violates the traditional principles of transcription in biology, as can be seen in the example of the HIV virus. Its reverse enzyme enzyme is capable of synthesizing DNA complementary to human nucleic acid from viral RNA. The process of synthesizing complementary DNA from RNA is called reverse transcription. This is the definition in biology of the process responsible for the integration of the hereditary information of the virus into the human genome.

In biology, the processes of transcription and translation are considered within the framework of protein biosynthesis. Although no protein synthesis occurs during the transcription process. But without it, translation (i.e., direct protein synthesis) is impossible. Transcription precedes translation.

Transcription and translation occurring in cells are consistent with the so-called dogma of molecular biology (put forward by F. Crick in the middle of the 20th century): the flow of information in cells goes in the direction from nucleic acids (DNA and RNA) to proteins, but never vice versa (that is, from proteins to nucleic acids). This means that nucleic acid can serve as an information matrix for protein synthesis, but protein cannot act as such for nucleic acid synthesis.

Transcription

Transcription is the synthesis of an RNA molecule on a DNA molecule. That is, DNA serves as a template for RNA synthesis.

Transcription is catalyzed by a number of enzymes, the most important being RNA polymerase. It should be remembered that enzymes are mainly proteins (this also applies to RNA polymerase).

RNA polymerase moves along the double strand of DNA, separates the strands, and on one of them, according to the principle of complementarity, builds an RNA molecule from nucleotides floating in the nucleus. Thus, RNA is essentially identical to a section of another DNA chain (on which synthesis does not occur), since the chains of the DNA molecule are also complementary to each other. Only in RNA thymine is replaced by uracil.

The synthesis of nucleic acids occurs in the direction from the 5" end of the molecules to their 3" end. In this case, the complementary chains are always antiparallel (directed in different directions). Therefore, RNA itself is synthesized in the 5"→3" direction, but along the DNA chain it moves in its 3"→5" direction.

The section of DNA where transcription occurs (transcripton, operon) consists of three parts: a promoter, a gene (in the case of mRNA, in general, the transcribed part) and a terminator.

To initiate (begin) transcription, various protein factors are needed that are attached to the promoter, after which RNA polymerase can be attached to the DNA.

Termination (end) of transcription occurs after RNA polymerase encounters one of the stop codons.

In eukaryotic cells, transcription occurs in the nucleus. After synthesis, RNA molecules undergo maturation here (unnecessary sections are cut out of them, the molecules take on the corresponding secondary and tertiary structure). Next, various types of RNA enter the cytoplasm, where they participate in the next process after transcription - translation.

Broadcast

Translation is the synthesis of a polypeptide (protein) chain on a messenger RNA molecule. In another way, translation can be described as the translation of information encoded using nucleotides (codon triplets) into information represented as a sequence of amino acids. This process occurs with the participation of ribosomes (which include ribosomal RNA) and transfer RNA. Thus, all three main types of RNA take part in direct protein synthesis.

During translation, ribosomes are attached to the beginning of the mRNA chain and then move along it towards its end. In this case, protein synthesis occurs.

Inside the ribosome there are two "spots" where two tRNAs can fit. Transfer RNAs entering the ribosome carry one amino acid. Inside the ribosome, the synthesized polypeptide chain is attached to a newly arrived amino acid bound to tRNA. After which this tRNA moves to another “place”, and the “old” one, already free from the growing polypeptide chain of tRNA, is removed from it. Another tRNA with an amino acid comes into the vacated space. And the process repeats.

The active center of the ribosome catalyzes the formation of a peptide bond between the newly arrived amino acid and the previously synthesized portion of the protein.

Two codons (6 nucleotides in total) of mRNA are placed in the ribosome. The anticodons of tRNA entering the ribosome must be complementary to the codons on which the ribosome “sits”. Different amino acids correspond to different tRNAs (differing in their anticodons).

Thus, each tRNA carries its own amino acid. It should be borne in mind that there are only about 20 amino acids involved in protein biosynthesis, and there are about 60 sense (denoting amino acid) codons. Therefore, different tRNAs can carry the same amino acid, but their anticodons correspond to the same amino acid.

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Transcription. Begin - beginning of transcription, End - end of transcription, DNA - DNA.

Transcription is the process of RNA synthesis using DNA as a template and 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

Transcription initiation is a complex process that depends on the DNA sequence in the vicinity of the transcribed sequence and on the presence or absence of various protein factors.

Transcription elongation

The moment at which RNA polymerase transitions from transcription initiation to elongation is not precisely determined. Three major biochemical events characterize this transition in the case of Escherichia coli RNA polymerase: the release of the sigma factor, the first translocation of the enzyme molecule along the template, and the strong stabilization of the transcription complex, which, in addition to the RNA polymerase, includes the growing RNA chain and the transcribed DNA. The same phenomena are also characteristic of eukaryotic RNA polymerases. The transition from initiation to elongation is accompanied by the rupture of bonds between the enzyme, promoter, transcription initiation factors, and in some cases, by the transition of RNA polymerase to a state of elongation competence. The elongation phase ends after the growing transcript is released and the enzyme dissociates from the template.

During the elongation stage, approximately 18 nucleotide pairs are untwisted in DNA. About 12 nucleotides of the DNA template strand forms a hybrid helix with the growing end of the RNA strand. As RNA polymerase moves through the template, unwinding of the DNA double helix occurs ahead of it, and restoration of the DNA double helix occurs behind it. At the same time, the next link of the growing RNA chain is released from the complex with the template and RNA polymerase. These movements must be accompanied by relative rotation of RNA polymerase and DNA. It is difficult to imagine how this could happen in a cell, especially during chromatin transcription. Therefore, it is possible that to prevent such rotation, RNA polymerase moving along DNA is accompanied by topoisomerases.

Elongation is carried out with the help of basic elongation factors, which are necessary so that the process does not stop prematurely.

Recently, evidence has emerged showing that regulatory factors may also regulate elongation. During the elongation process, RNA polymerase pauses at certain parts of the gene. This is especially clearly seen at low concentrations of substrates. In some areas of the matrix there are long delays in the advancement of RNA polymerase, the so-called. pauses are observed even at optimal substrate concentrations. The duration of these pauses can be controlled by elongation factors.