After deciphering the genetic code, the question arose: how is information transferred from DNA to protein? Biochemical studies have established that the bulk of DNA in a cell is localized in the nucleus, while protein synthesis occurs in the cytoplasm. This territorial separation of DNA and protein synthesis led to the search for a mediator. Since protein synthesis proceeded with the participation of ribosomes, RNA was put forward as an intermediary. A diagram was created illustrating the direction of the flow of genetic information in a cell:

DNA → RNA → protein

It has been called the central dogma of molecular biology. F. Crick postulated that the synthesis of macromolecules according to this scheme is carried out according to the matrix principle. It took many years to prove the correctness of this postulate.

Initially, it was assumed that ribosomal RNA played the role of an intermediary (“one gene - one ribosome - one protein”). However, this assumption soon became clear. It was shown that the number of ribosomes does not change during protein synthesis; no new RNA is synthesized and therefore no new information is received. Soon, a fraction of unstable RNA was found in the composition of ribosomes, the molecules of which are loosely held on the ribosome with the help of Mg cations. Molecular hybridization has shown that this RNA molecules are copies of certain sections of DNA. She got the name matrix, or messenger RNA. It was also called earlier RNA-intermediary and messenger-RNA. The complementarity of these molecules to certain DNA regions indicated that they are synthesized according to the template type on DNA.

Gradually, the entire path of information transfer from DNA to protein was elucidated. It consists of two stages: transcriptions and broadcasts. At the stage of transcription, the reading and transfer of genetic information from DNA to mRNA occurs. The transcription process proceeds in three stages: initiation, elongation and termination. Information is read from only one DNA strand (+ strand), since, based on the properties of the genetic code, complementary DNA sections cannot encode the structure of the same protein due to the lack of complementary degeneracy of the code. The RNA polymerase enzyme, which consists of four subunits (ααββ") and does not have specificity for the DNA source, conducts transcription. At the initial stage of transcription - initiation - the fifth subunit, the so-called s-factor, is attached to the enzyme, which recognizes a specific DNA region, promoter. Promoters are not transcribed. They are recognized by the s-factor by the presence of a specific nucleotide sequence in them. In bacterial promoters, it is called the Pribnow block and has the form TATAAT (with slight variations). The enzyme RNA polymerase attaches to the promoter. The growth of the mRNA chain occurs in one direction, the transcription rate is ≈ 45-50 nucleotides per 1 second.At the initiation stage, only a short chain of 8 nucleotides is synthesized, after which the s-factor is separated from the RNA polymerase and the elongation stage begins. from which information is read is called a transcripton.It ends with a termi nator - a specific nucleotide sequence that plays the role of a stop signal. Having reached the terminator, the RNA polymerase enzyme stops working and, with the help of protein termination factors, is separated from the matrix.

In bacterial cells, the resulting mRNA molecules can immediately act as templates for protein synthesis; broadcast. They connect to ribosomes, to which transport RNA (tRNA) molecules simultaneously deliver amino acids. Transfer RNA chains are approximately 70 nucleotides long. A single-stranded tRNA molecule has sites of complementary pairing, which include active centers: a site for recognition of tRNA by the enzyme tRNA synthetase, which attaches the corresponding activated amino acid to tRNA; an acceptor is a site to which an amino acid is attached, and an anticodon loop.

Anticodon is a triplet complementary to the corresponding codon in the mRNA molecule. The codon-anticodon interaction proceeds by the type of complementary pairing, during which an amino acid is attached to a growing protein chain. The initiating codon in various mRNAs is the AUG codon corresponding to the amino acid methionine. Therefore, tRNA with the UAC anticodon coupled to the activated amino acid methionine is the first to approach the template. Enzymes that activate amino acids and bind them to tRNA are called aminoacyl-tRNA synthetases. All stages of protein biosynthesis (initiation, elongation, termination) are served by protein translation factors. Prokaryotes have three of them for each stage. At the end of the mRNA template are nonsense codons that are not read and mark the end of translation.

In the genome of many organisms, from bacteria to humans, genes and their corresponding tRNAs have been found that perform non-standard codon reading. This phenomenon has been named broadcast ambiguity.

It allows avoiding the negative consequences of errors that occur in the structure of mRNA molecules during transcription. Thus, when nonsense codons appear inside the mRNA molecule that can prematurely stop the transcription process, the suppression mechanism is activated. It consists in the fact that an unusual form of tRNA appears in the cell with an anticodon complementary to the nonsense codon, which should not be normal. Its appearance is the result of the action of a gene that performs a base change in the tRNA anticodon, which is similar in composition to the nonsense codon. As a result of such a replacement, the nonsense codon is read as a normal significant codon. Such mutations are called suppressor, because. they suppress the original mutation that led to the appearance of the nonsense codon.

DNA - the carrier of all genetic information in the cell - does not take a direct part in the synthesis of proteins. In animal and plant cells, DNA molecules are contained in the chromosomes of the nucleus and are separated by a nuclear membrane from the cytoplasm, where proteins are synthesized. To ribosomes - protein assembly sites - an information-carrying mediator is sent from the nucleus, capable of passing through the pores of the nuclear membrane. Messenger RNA (i-RNA) is such an intermediary. According to the principle of complementarity, it is read from DNA with the participation of an enzyme called RNA polymerase. The process of reading (or rather, writing off), or RNA synthesis, carried out by RNA polymerase, is called transcription (Latin transcriptio - rewriting). Messenger RNA is a single-stranded molecule, and transcription comes from one strand of a double-stranded DNA molecule. If the nucleotide G is in the transcribed DNA strand, then RNA polymerase includes C in the RNA, if it is T, it includes A, if it is A, it includes y (the RNA does not include T) (Fig. 46). In length, each of the mRNA molecules is hundreds of times shorter than DNA. Messenger RNA is not a copy of the entire DNA molecule, but only part of it - one gene or a group of adjacent genes that carry information about the structure of proteins necessary to perform one function. In prokaryotes, this group of genes is called an operon. You will read about how genes are combined into an operon and how transcription control is organized in the section on protein biosynthesis. At the start of each operon is a kind of landing site for RNA polymerase called a promoter. This is a specific sequence of DNA nucleotides that an enzyme recognizes through chemical affinity. Only by attaching to the promoter, RNA polymerase is able to start the synthesis of mRNA. Having reached the end of the operon, the enzyme encounters a signal (in the form of a certain sequence of nucleotides) indicating the end of reading. The finished mRNA moves away from DNA and goes to the site of protein synthesis. There are four stages in the described transcription process:

1) Binding of RNA polymerase to the promoter;

2) Initiation - the beginning of synthesis. It consists in the formation of the first phosphodiester bond between ATP or GTP and the second nucleotide of the synthesized RNA molecule;

3) elongation - the growth of an RNA chain, i.e., the sequential attachment of nucleotides to each other in the order in which complementary nucleotides are in the transcribed DNA strand. The elongation rate reaches 50 nucleotides per second;

4) termination - completion of the synthesis of mRNA.

RNA biosynthesis - transcription - the process of reading genetic information from DNA, in which the DNA nucleotide sequence is encoded as an RNA nucleotide sequence. Used as energy and substrate - nucleoside-3-phosphate with ribose. It is based on complementarity principle- a conservative process - a new single-stranded RNA is synthesized during the entire interphase, starts in certain areas - promoters, ends in terminators, and the section between them - an operon (trancrypton) - contains one or more functionally related genes, sometimes contains genes that do not encode proteins. Transcription differences: 1) individual genes are transcribed. 2) no primer required. 3) ribose is included in RNA, not deoxyribose.

Transcription steps: 1) binding of RNA polymerase to DNA. 2) initiation - the formation of an RNA chain. 3) elongation or growth of the RNA chain. 4) termination.

Stage 1 - the site with which RNA polymerase binds is called a promoter (40 nucleotide pairs) - it has a site for recognition, attachment, initiation. RNA polymerase, recognizing the promoter, sits on it and a closed promoter complex is formed, in which DNA is spiralized and the complex can easily dissociate and pass into an open promoter complex - the bonds are strong, the nitrogenous base turns outward.

Stage 2 - initiation RNA synthesis consists in the formation of several links in the RNA chain, the synthesis begins on one DNA strand 3'-5' and goes in the direction 5'-3'. The stage ends with the separation of the b-subunit.

Stage 3 - elongation- elongation of the RNA chain - occurs due to Core-rRNA polymerase. The DNA strand is despiralized on 18 pairs, and on 12 - a hybrid - a common hybrid of DNA and RNA. RNA polymerase moves along the DNA chain, and after the restoration of the DNA chain. In eukaryotes, when the RNA reaches 30 nucleotides, a protective CEP structure is formed at the 5' end.

Stage 4 - termination- occurs on terminators. In the chain there is a site rich in GC, and then from 4 to 8 consecutive A. After passing through the site, a hairpin is formed in the RNA product and the enzyme does not go further, the synthesis stops. An important role is played by the protein termination factor - rho and tower. While the synthesis was going on, pyrophosphate inhibited the rho protein, because the enzyme has stopped (hairpin) the synthesis of phosphoric acid has stopped. The Rho protein is activated and exhibits nucleoside phosphatase activity, which leads to the release of RNA, RNA polymerase, which is further combined with the subunit.

Processing - RNA maturation. Includes: 1) the formation of CEP at the 5'-end, is involved in attachment to the ribosome. 2) polyadenylation occurs at the 3'-end and a tail of one hundred to two hundred adenyl nucleotides is formed, it protects the '-end from the action of nucleases and helps to pass through nuclear pores and plays a role in attaching to the ribosome. 3) splicing - non-coding sequences are cut out - introns. This happens in two ways: a) is carried out by the spliceosome - it is a nucleoprotein containing a number of proteins and small nuclear RNA. In the beginning, introns are looped out, leaving only coding sequences - exons. Endonuclease enzymes are cut and ligases ligate the remaining exons. THEN. the introns are gone. Alternative splicing - on the same nucleic acid sequence, RNA forms several proteins. Self-splicing is the self-removal of introns. Splicing disorders: 1) systemic lupus erythematosus. 2) phenylketonuria. 3) hemoglobinopathy. Matrix RNA of prokaryotes is not processed, because they don't have introns. tRNA processing. The tRNA precursor is cleaved and the nucleotide 5'-3' Q P is cleaved off. The CCA sequence with an OH group is attached to the 3'-end, and a phosphorylated purine base is attached to the 5'-end. Duhydrouridine loop - ARSase. rRNA processing. The rRNA precursor, proribosomal 45S RNA, is synthesized in the nucleolus and exposed to ribonucleases to form 5.8S 18S 28S. They are 70% spiralized. rRNA plays a role in the formation of the ribosome and is involved in catalytic processes. The subunit is formed from rRNA in the nucleus. The small subunit is 30S, the large subunit is 50S and the ribosome 70S is formed in prokaryotes, in eukaryotes 40S + 60S = 80S. Ribosome formation occurs in the cytoplasm.

Ribosome sites for RNA binding: 1) in small subunits that have the Shine-Dalgorn mRNA sequence 5'GGAGG3' 3'CCUCC5'. Messenger RNA is attached to the small subunit. In eukaryotes, CEP-binding site for mRNA. tRNA binding site: a) P-site - peptidyl center for binding mRNA to the growing peptide chain - peptidyl-tRNA-binding. b) A-section - for the connection of tRNA with an amino acid - aminoacyl site 2) In the large subunit, the E-section with peptidyl transferase activity.

reverse transcription characteristic of retroviruses or viruses containing RNA - HIV infection virus, oncoviruses.

On the RNA chain, DNA synthesis occurs under the action of the enzyme reverse transcriptase or reversetase, or DNA RNA polymerase. Invading the host cell, DNA synthesis occurs, into which it is integrated into the host DNA and the transcription of its RNA and the synthesis of its own proteins begin.

Genetic code, its characteristics. The genetic code is the nucleotide sequence of the rRNA molecule that contains code words for each amino acid. It consists in a certain sequence of nucleotides in the DNA molecule.

Characteristic. 1) the genetic code is triplet - i.e. each a/k is encrypted with three nucleotides. 2) the genetic code for a / c is degenerate or redundant - the vast majority of a / c is encoded by several codons. A total of 64 triplets are formed, of which 61 triplets encode a certain a / c, and three triplets - AUG, UAA, UGA are nonsense codons, because they do not encode any of the 20 a / c, they perform the function of terminating the synthesis. 3) The genetic code is continuous, there are no punctuation marks, i.e. signals indicating the end of one triplet and the beginning of another. The code is linear, unidirectional, continuous. For example - ATSGUTSGATSTS. 4) the AUG triplet serves as the synthesis activation codon. 5) The genetic code is universal.

22. Broadcast - protein biosynthesis. Translation stages: 1) initiation. 2) elongation. 3) termination. Initiation- A/C is activated.

The initiating aatRNA will interact with the 1 a/c of ​​the future protein only with the carboxyl group, and the 1 a/c can give only the NH 2 group for synthesis, i.e. protein synthesis starts at the N-terminus.

Assembly of the initiating complex on a small subparticle. Factors: 30S mRNA fomylmethionyl tRNA IF 123 Mg 2+ GTP is an energy source

The small subunit loaded with initiation factors finds the start codon AUG or GUG on the mRNA and sets the reading frame according to it; the start codon is placed in the P site. Formlmethionyl tRNA approaches it, which is accompanied by the release of IF 3 factor, then the large subunit joins and IF 1 and IF2 are released, hydrolysis of 1GTP occurs and a ribosome is formed. Elongation is the working cycle of the ribosome. Includes three steps: 1) binding of aatRNA to the A-site; P-site is occupied – elongation factors EF-TU, EF-TS and GTP are needed. Elongation factors in prokaryotes: EF-TU, EF-TS, EF-G. 3 )Translocation– first, the EF-G deacylated tRNA of the P-site leaves the ribosome, moving 1 triplet towards the 3’ end; the movement of the peptide from A to the P-site - GTP is used and the elongation factor - EF-G-translocase, A - the site is again free and the process is repeated. Termination– recognition of the termination codons UAA, UGA, UAG with the help of releasing factors RF 1 2 3. When the terminal codon enters the A-site, tRNA is not attached to it, but one of the termination factors is attached, which blocks elongation, which is accompanied by activation of the esterase activity of peptidyl transferase site E. Hydrolysis of ester bonds between the peptide and tRNA occurs, the ribosome leaves the peptide, tRNA and dissociates into subunits, which can then be used.

Structure formation occurs simultaneously with the help of chaperone proteins - heat shock proteins. The synthesis of one peptide bond consumes 1ATP for aminoacylation of tRNA (attachment of an amino acid), 1GTP for the connection of aatRNA with the A-site, and 1GTP for translocation. Energy consumption is about 4 macroergic bonds for the synthesis of one peptide bond.

23. Lactose operon. Replication is regulated by the concentration of the Dna protein and guanosine tetraphosphate. The main regulation of gene expression is carried out at the level of transcription (depending on the stage of cell development, all factors, the action of hormones and other regulatory components). In different tissue cells, only 5% of genes are expressed, 97% are silent - junk DNA - transcription regulators are chronomeres and a number of regulatory sequences. If the attachment of a regulatory protein to DNA causes transcription, then this is a positive (+) regulation, if transcription suppression is a negative (-) regulation. Positive regulation- the gene is turned off, the attachment of the regulator protein leads to the beginning of synthesis, as a result, the gene is turned on. THEN. a regulatory protein can be an inducer or an activator . Negative regulation- the gene is turned on, RNA synthesis is in progress, if a protein regulatory factor (inhibitor or repressor of protein synthesis) is added, the gene is turned off. Many hormones and other factors influence the attachment of the regulator protein. E. coli lactose operon- negative regulation. The main elements of its work: in the DNA molecule - a regulator site, a promoter, a pro-operon and three structural genes: lag 1, lag 2, lag 3 and terminator. Lag 1 - carries out the synthesis of the enzyme lactase or beta-galactosidase. Lag 2 is a permiase enzyme involved in the transport of lactose across the membrane. Lag 3 is the enzyme transacylase. Regulator - mRNA synthesis on the ribosome, leads to the formation of a repressor protein, it attaches to the operator (because it has an affinity), sits on it, and since it the regions of the promoter and operon overlap - RNA polymerase cannot attach to the promoter and transcription is turned off. Glucose and galactose provide repressor and operator similarity. If there is no similarity, lactose interacts with the repressor, changing its transformation, and it does not sit on the operon, because loses resemblance to it. RNA polymerase sits on the promoter and transcription of messenger RNA begins. Lactose is an inducer, and the process is induction, a form of downregulation, so called because transcription is terminated by the addition of a repressor and its cleavage initiates synthesis. Positive regulation - TATA factor– has similarities to the TATA-box area. The TATA factor sits on the TATA box - a signal for RNA polymerase to recognize its promoter, sits on it and starts transcription of adjacent genes. In prokaryotes, negative regulation prevails; for eukaryotes, this is not beneficial. Enhancer sites (transcriptional enhancers) + regulatory protein leads to increased transcription. Sincers + regulatory protein à turns off transcription and changes the structure of chromosomes.

According to the sequencing principle, information is transferred from DNA to RNA to proteins: DNA -> RNA -> protein. In this regard, let us turn to the content of transcription (from lat. transcriptio- rewriting), along with DNA replication, which is the most important genetic and molecular mechanism. Transcription is similar to replication in many ways, but, of course, it has numerous features. One of them is that when elucidating the content of transcription, it is imperative to take into account the structure of genes. The fact is that all the structural units of genes are reproduced in replication, which is not the case with transcription.

Traditionally, a gene is defined as a unit of hereditary information that determines the performance of a certain function by an organism. A gene consists of a regulatory and coding part. Only the coding part, which consists of exons and introns, is transcribed. This transcription is characteristic of immature RNA. It finds its continuation in the final stage of transcription, in which all introns are excluded from the immature RNA, and the remaining exons are combined. At the site of the promoter, RNA polymerase binds to the regulatory part of the gene, which, as a result, initiates the start of transcription on one of the two DNA strands. On fig. Figure 6.8 shows a diagram of the structure of a eukaryotic gene, as well as mature and immature RNA.

Some of the terms used above obviously need characterization.

Rice. 6.8.

Promoter (from fr. promoter founder, initiator) is a sequence of DNA nucleotides that allows you to regulate gene expression. It is located near the 5" gene and, therefore, immediately before that part of the gene that encodes RNA. An essential feature of the promoter is its specific interaction with DNA-dependent proteins, which determine the start of transcription through RNA polymerase. Such proteins are called transcription factors.

Along with the promoter, the regulatory part of the gene includes nucleotide sequences that also have a significant effect on gene expression. Enhancers (English, enhancer- amplifier, magnifier) ​​amplify it, and silencers (from English, silencers- silencer) suppress, but not by themselves, but only if they are exposed to transcription factors. The spatial position of enhancers and silencers is not clearly defined; they may be at a smaller or greater distance from the promoter.

exon (english) expressed region- region of expression) - a section of a gene that encodes mature RNA and proteins. Exons are the primary genetic units on which the appearance of the entire biological world depends decisively. It is their recombination that leads to the formation of new genes and proteins. Only 1.5% of the DNA gene composition determines the synthesis of proteins. Another part of this composition is either not transcribed at all, or determines the structure of such RNA varieties, for example, transfer RNAs, which do not have the function of protein synthesis.

Intron (from English, intervening regions- intermediate regions) - a section of a gene that does not contain information about mature RNA and proteins. The biological functions of introns are studied much worse than the functions of exons. There is also great controversy about their origin: whether they arose together with prokaryotes, or together with eukaryotes, or even later than them. One human gene contains on average 8.8 exons and 7.8 ingrons, but ingrons are on average about 25 times longer than exons.

After what has been said, it is not difficult to imagine in general terms the entire process of transcription (Fig. 6.9).

Rice. 6.9.

Stage of initiation. Under the influence of enzymes, in particular enhancers, having joined the promoter, RNA polymerase breaks nitrogenous bases (indicated in Fig. 6.9 by short vertical lines) and selects the DNA branch that becomes the transcription template (in Fig. 6.9. this is the bottom line). It also creates a transcription eye (in Figure 6.9 it is a triangular lid). At the same time, 10-20 pairs of non-cleotids are exposed for the elongation stage. Interestingly, in the case of transcription, there is no need to form a primer characteristic of the DNA replication process. Transcription is done without a primer.

elongation stage. Under the action of RNA polymerase, RNA is formed in the region of the transcriptional eye. Unlike DNA polymerase, RNA polymerase is not able to correct the correctness of the synthesis of the RNA chain and correct the mistakes made. If difficulties arise during the synthesis, the movement of RNA polymerase is suspended. As a result, the probability of erroneous assembly of RNA is reduced. Transcription does not stop, the eye moves away from the promoter. In those areas that have passed the peephole, the duplex structure of DNA is restored. The chain of the synthesized RNA gradually lengthens. It grows in the direction of 5"-3".

Termination stage. It occurs due to the effect of auxiliary factors on RNA polymerase. Once the transcriptional region is reached by the exonucleases, transcription stops and the RNA polymerase and RNA separate from each other. DNA completely restores its duplex structure.

Until now, we have considered PI IK transcription in the most general terms, abstracting from several significant circumstances, in particular, the presence of different types of both RNA and RNA polymerases was not taken into account. There are the following types of RNA:

Information about all types of RNA is contained in DNA. However, not all of them are transcribed directly on template DNA.

Some RNAs are modifications of previously transcribed RNAs. For us, getting acquainted with the foundations of molecular genetics, of greatest interest are RNAs involved directly in the synthesis of proteins. There are only 5 types of them (Table 6.4).

Table 6.4

RNA involved in protein synthesis

* Messenger RNA - the same as messenger RNA; ** SPR - abbr. English signal recognition particle- particles that recognize signals.

Transcription of all RNAs occurs through the action of certain RNA polymerases or their combinations. In table. 6.5 shows the main three types of RNA polymerases.

Table 6.5

Types of RNA polymerases

’ Small (short) RGCs are different from long RNAs. MicroRNAs are a type of small RNAs that make up 98% of all ribonucleotide material.

In conclusion of the section, we note that, along with direct transcription, reverse transcription is also possible. The ability to transcribe RNA into DNA is possessed by retroviruses, in particular HIV, which is responsible for AIDS. The retrovirus enters the cell. A special enzyme reverse transcriptase carries out the transcription of RNA -» DNA. Then, on the resulting DNA strand, as on a matrix, the second DNA strand is completed. After that, the cycle DNA -> RNA -» proteins is realized. Some eukaryotes contain the enzyme telomerase, which also initiates reverse transcription. The phenomenon of reverse transcription must be taken into account when formulating the sequence principle. It should not be interpreted as negating reverse transcription.

• A gene consists of a regulatory and coding part.
• The coding part of a gene includes exons and introns.
• Introns are not transcribed into mature RNA.
• Transcription includes the steps of initiation, elongation, and termination.
• There are various types and types of both PIIK and PIK transcription polymerases.
• The synthesis of any RNA is carried out either by one or several polymerases, and not without the participation of protein enzymes.

• SakharkarM. K., Chow V. T., Kangueane R. Distributions of Exons and Introns in the HumanGenome // In Silicio Biology. 2004 Vol. 4. No. 4. P. 387-393.

Transcription in biology is a multi-stage process of reading information from DNA, which is a component. 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 activity, because these organic compounds are involved in all metabolic processes, are structural components of many tissues and organs, play a signaling, regulatory and protective role in the body.

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

1. Initiation.
2. Elongation (growth of the 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 the DNA template. Moreover, not only information ribonucleic acids are formed in this way, 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 to 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 template DNA chain. This enzyme has two β-subunits, one α-subunit and one σ-subunit. The first two components perform the function of forming the body of the enzyme, and the remaining two are responsible for retaining the enzyme on the DNA molecule and recognizing the promoter part of the deoxyribonucleic acid, respectively.

By the way, the sigma factor is one of the signs by which this or that gene is recognized. For example, the Latin letter σ with index 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 is somewhat more complicated in animals and plants. Firstly, in each cell there are not one, but as many as 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 the 5S RNA subunits of the ribosome).
2. RNA polymerase II. Its task is to synthesize normal informational (matrix) ribonucleic acids, which are further involved in translation.
3. RNA polymerase III. The function of this type of polymerase is to synthesize as well as 5S-ribosomal RNA.

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

Transcription meaning

The RNA molecule, which is formed on the DNA matrix, subsequently attaches to the ribosomes, where information is read from it and a 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, first of all, the basis for the most important enzymes of all biochemical reactions.

Transcription in biology is also a source of rRNAs, which are also tRNAs that are involved in the transfer of amino acids during translation to these non-membrane structures. snRNAs (small nuclear nuclei) 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 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 needed at the moment to maintain life. Therefore, transcription in biology is the main stage in the work of each individual cell of the body.