Processing is ... RNA processing (posttranscriptional modifications of RNA)

It is this stage that distinguishes the realization of the available genetic information from cells such as eukaryotes and prokaryotes.

Interpreting this concept

In English this term means "processing, processing". Processing is the process of formation of mature molecules of ribonucleic acid from pre-RNA. In other words, this is a set of reactions that lead to the transformation of primary transcription products (pre-RNA of different types) into already functioning molecules.

Regarding the processing of p- and tRNA, it often boils down to cutting off excess molecules from the ends of the molecules. If we talk about mRNA, then here it can be noted that in eukaryotes this process is multistep.

So, after we have already learned that processing is the transformation of the primary transcript into a mature RNA molecule, we need to consider its features.

The main features of the concept

This includes the following:

• Modification of both the ends of the molecule and RNA, along which specific nucleotide sequences are added to them, showing the place of the beginning (end) of the translation;
• Splicing - clipping of non-informative sequences of ribonucleic acid, which correspond to introns of DNA.

As for prokaryotes, their mRNA is not subject to processing. It has the ability to work immediately after the synthesis is completed.

Where is the process under consideration?

In any organism, RNA processing takes place in the nucleus. It is carried out by means of special enzymes (by their group) for each individual type of molecule. Also, translation products such as polypeptides that are directly read from mRNA can be processed. These changes are the so-called precursor molecules of most proteins - collagen, immunoglobulins, digestive enzymes, some hormones, after which their real functioning begins in the body.

We have already learned that processing is the process of the formation of mature RNA from pre-RNA. Now it's worth digging into the nature of the ribonucleic acid itself.

RNA: chemical nature

This is a ribonucleic acid, which is a copolymer of pyrimidine and purine ribonucleotides, which are connected to each other, just like in DNA, 3 '- 5'-phosphodiester bridges.

Despite the fact that these two types of molecules are similar, they differ by several features.

Distinctive features of RNA and DNA

First, there is a carbon residue in ribonucleic acid, to which pyrimidine and purine bases, phosphate groups, ribose, and 2'-deoxyribose are attached.

Secondly, the pyrimidine components also differ. Similar constituents are the nucleotides of adenine, cytosine, guanine. In RNA, instead of thymine, uracil is present.

Thirdly, RNA has a 1-chain structure, and DNA is a 2-chain molecule. But in the chain of ribonucleic acid there are regions with opposite polarity (complementary sequence), due to which its single chain is able to fold and form "hairpins" - structures with 2-helical characteristics (as shown in the figure above).

Fourthly, since RNA is a single chain that is complementary to only one of the DNA chains, guanine need not be present in it in the same content as cytosine, and adenine is like uracil.

Fifthly, RNA can be hydrolysed to 2 ', 3'-cyclic diesters of mononucleotides by alkali. The role of the intermediate in hydrolysis is played by 2 ', 3', 5-triester, incapable of forming a similar process for DNA because it lacks 2'-hydroxyl groups. In comparison with DNA, the alkaline lability of ribonucleic acid is a useful property for both diagnostic and analytical purposes.

The information contained in the 1-stranded RNA, as a rule, is realized as a sequence of pyrimidine and purine bases, in other words, as the primary structure of the polymer chain.

This sequence is complementary to the gene chain (coding) with which RNA is "read". Because of this property, the ribonucleic acid molecule can specifically bind to the coding chain, but is unable to do this with a non-coding DNA chain. The sequence of RNA, in addition to replacing T by U, is analogous to that related to the non-coding gene chain.

Types of RNA

Virtually all of them are involved in such a process as protein biosynthesis. The following types of RNA are known:

1. Matrix (mRNA). These are molecules of cytoplasmic ribonucleic acid, which serve as protein synthesis matrices.
2. Ribosomal (rRNA). It is a molecule of cytoplasmic RNA that plays the role of such structural components as ribosomes (organelles involved in protein synthesis).
3. Transport (tRNA) . These are transport ribonucleic acid molecules that participate in the translation (translation) of mRNA information into a sequence of amino acids already in proteins.

A significant portion of RNA in the form of the first transcripts that are formed in eukaryotic cells, including mammalian cells, is prone to degradation in the nucleus, and does not play an informational or structural role in the cytoplasm.

In human cells (cultured), a class of small nuclear ribonucleic acids that do not directly participate in protein synthesis but has an effect on RNA processing, as well as a common cellular "architecture", has been found. Their sizes vary, they contain 90-300 nucleotides.

Ribonucleic acid is the main genetic material in a number of viruses of plants, animals. Some viruses containing RNA never go through a stage such as reverse transcription of RNA into DNA. However, for many animal viruses, for example for retroviruses, the reverse translation of their RNA genome, directed by RNA-dependent reverse transcriptase (DNA polymerase), is characteristic with the formation of a 2-helical DNA copy. In most cases, the emerging 2-spiral DNA transcript is introduced into the genome, further ensuring the expression of viral genes and the development of new copies of RNA genomes (also viral).

Posttranscriptional modifications of ribonucleic acid

Its molecules, synthesized with RNA polymerases, are always functionally inactive, act as precursors, namely pre-RNA. They are transformed into mature molecules only after the corresponding posttranscriptional modifications of RNA have passed - the stages of its maturation.

The formation of mature mRNA is read during the synthesis of RNA and polymerase II at the elongation stage. Already to the 5'-end of the gradually growing strand, RNA is attached by the 5'-end of the GTP, then the orthophosphate is cleaved off. Further, guanine is methylated with the advent of 7-methyl-GTP. This special group, which is part of the mRNA, is called a "cap" (cap or cap).

Depending on the type of RNA (ribosomal, transport, matrix, etc.), the precursors undergo various successive modifications. For example, mRNA precursors undergo splicing, methylation, capping, polyadenylation, and sometimes editing.

Eukaryotes: general characteristic

A cell of eukaryotes acts as a domain of living organisms, and it contains a nucleus. In addition to bacteria, archaea, any organisms are nuclear. Plants, fungi, animals, including a group of organisms called protists, all act as eukaryotic organisms. They are both 1-cellular and multicellular, but all have a common plan of the cellular structure. It is believed that these so different organisms have the same origin, so that the nuclear group is perceived as a monophyletic taxon of the highest rank.

Based on common hypotheses, eukaryotes arose 1.5-2 billion years ago. An important role in their evolution is given to symbiogenesis, a symbiosis of the eukaryotic cell, which had a nucleus capable of phagocytosis, and bacteria swallowed by it, the precursors of plastids and mitochondria.

Prokaryotes: general characteristic

These are 1-cell living organisms that do not have a nucleus (decorated), the remaining membrane organoids (internal). The only large annular 2-stranded DNA molecule containing the bulk of the genetic cell material is one that does not form a complex with histone proteins.

Prokaryotes include archean and bacteria, including cyanobacteria. Descendants of nuclear-free cells - organelles of eukaryotes - plastids, mitochondria. They are subdivided into 2 taxa within the domain's rank: Archea and Bacteria.

These cells do not have a nuclear envelope, DNA packaging occurs without the involvement of histones. The type of their food is circumspect, and the genetic material is represented by one DNA molecule, which is closed in a ring, and there is only 1 replicon. Prokaryotes remain organoids, which have a membrane structure.

Difference between eukaryotes and prokaryotes

The fundamental feature of eukaryotic cells is related to the presence in them of a genetic apparatus, which is located in the nucleus, where it is protected by a membrane. Their DNA is linear, associated with histone proteins, other chromosomal proteins that are absent in bacteria. As a rule, in their life cycle there are 2 nuclear phases. One has a haploid set of chromosomes, and subsequently merging, two haploid cells form a diploid, which already contains the 2nd set of chromosomes. It also happens that with the subsequent division the cell again becomes haploid. This kind of life cycle, as well as diploidity in general, is not characteristic of prokaryotes.

The most interesting difference is the presence of special organelles in eukaryotes, which have their own genetic apparatus and multiply by fission. These structures are surrounded by a membrane. These organelles are plastids and mitochondria. In terms of vital activity and structure, they are remarkably similar to bacteria. This circumstance has prompted scientists to think about the fact that they are descendants of bacterial organisms that have entered into a symbiosis with eukaryotes.

Prokaryotes have a small amount of organelles, none of which is surrounded by a 2nd membrane. In them there is no endoplasmic reticulum, Golgi apparatus, lysosomes.

Another important difference between eukaryotes and prokaryotes is the presence of endocytosis in eukaryotes, including phagocytosis in most groups. The latter is called the ability to capture by imprisonment in a membrane bubble, and then digest various solids. This process provides the most important protective function in the body. The origin of phagocytosis, presumably, is due to the fact that their cells are of medium size. Prokaryotic organisms are incommensurably smaller, therefore, in the course of the evolution of eukaryotes, a need arose associated with supplying the cell with a significant amount of food. As a result, the first mobile predators appeared among them.

Processing as one of the stages of protein biosynthesis

This is the second stage that begins after transcription. Protsessing proteins occurs only in eukaryotes. This maturation of mRNA. To be precise, this is the removal of the areas that do not encode the protein, and the connection of controllers.

Conclusion

This article describes what processing is (biology). Also, what is RNA is described, its types and post-transcriptional modifications are listed. The distinctive features of eukaryotes and prokaryotes are considered.

Finally, it is worth recalling that processing is the process of the formation of mature RNA from pre-RNA.