It is this stage that distinguishes the implementation of the available genetic information in cells such as eukaryotes and prokaryotes.
Interpretation of this concept
Translated from English, this term means "processing, processing." Processing is the process of formation of mature ribonucleic acid molecules from pre-RNA. In other words, this is a set of reactions that lead to the transformation of primary transcription products (pre-RNA of various types) into already functioning molecules.
As for the processing of r- and tRNA, it most often comes down to cutting off excess fragments from the ends of molecules. If we talk about mRNA, then here it can be noted that in eukaryotes this process proceeds in many stages.
So, after we have already learned that processing is the transformation of a primary transcript into a mature RNA molecule, it is worth moving on to considering its features.
Main features of the concept under consideration
This includes the following:
- modification of both the ends of the molecule and RNA, during which specific nucleotide sequences are attached to them, showing the place of the beginning(end of) broadcast;
- splicing - cutting off non-informative ribonucleic acid sequences that correspond to DNA introns.
As for prokaryotes, their mRNA is not subject to processing. It has the ability to work immediately after the end of the synthesis.
Where does the process in question take place?
In any organism, RNA processing takes place in the nucleus. It is carried out by means of special enzymes (their group) for each individual type of molecule. Translation products such as polypeptides that are directly read from mRNA can also be processed. The so-called precursor molecules of most proteins - collagen, immunoglobulins, digestive enzymes, some hormones - undergo these changes, after which their real functioning in the body begins.
We have already learned that processing is the process of forming mature RNA from pre-RNA. Now it's worth delving into the nature of ribonucleic acid itself.
RNA: chemical nature
This is a ribonucleic acid, which is a copolymer of pyrimidine and purine ribonucleitides, which are connected to each other, just like in DNA, by 3' - 5'-phosphodiester bridges.
Despite the fact that these 2 kinds of molecules are similar, they differ in several ways.
Distinguishing features of RNA and DNA
Firstly, ribonucleic acid has a carbon residue, to which pyrimidine and purinebases, phosphate groups - ribose, while DNA has 2'-deoxyribose.
Secondly, the pyrimidine components also differ. Similar components are the nucleotides of adenine, cytosine, guanine. RNA contains uracil instead of thymine.
Thirdly, RNA has a 1-stranded structure, while DNA is a 2-stranded molecule. But the ribonucleic acid strand contains regions of opposite polarity (complementary sequence) that allow its single strand to fold up and form "hairpins" - structures endowed with 2-stranded characteristics (as shown in the figure above).
Fourthly, due to the fact that RNA is a single strand that is complementary to only one of the DNA strands, guanine does not have to be present in it in the same content as cytosine, and adenine as uracil.
Fifth, RNA can be hydrolyzed with alkali to 2', 3'-cyclic diesters of mononucleotides. The role of an intermediate product in hydrolysis is played by 2', 3', 5- triester, which is incapable of formation in the course of a similar process for DNA due to the absence of 2'-hydroxyl groups in it. Compared to DNA, the alkaline lability of ribonucleic acid is a useful property for both diagnostic and analytical purposes.
The information contained in 1-stranded RNA is usually realized as a sequence of pyrimidine and purine bases, in other words, in the form of the primary structure of the polymer chain.
This sequencecomplementary to the gene chain (coding) from which the RNA is “read”. Because of this property, a ribonucleic acid molecule can specifically bind to a coding strand, but is unable to do so with a non-coding DNA strand. The RNA sequence, except for the replacement of T with U, is similar to that of the non-coding strand of the gene.
RNA types
Almost all of them are involved in such a process as protein biosynthesis. The following types of RNA are known:
- Matrix (mRNA). These are cytoplasmic ribonucleic acid molecules that act as templates for protein synthesis.
- Ribosomal (rRNA). This is a cytoplasmic RNA molecule that acts as structural components such as ribosomes (organelles involved in protein synthesis).
- Transport (tRNA). These are molecules of transport ribonucleic acids that take part in the translation (translation) of mRNA information into an amino acid sequence already in proteins.
A significant part of RNA in the form of 1st transcripts, which are formed in eukaryotic cells, including mammalian cells, is subject to the process of degradation in the nucleus, and does not play an informational or structural role in the cytoplasm.
In human cells (cultivated) a class of small nuclear ribonucleic acids was found, which are not directly involved in protein synthesis, but affect RNA processing, as well as the overall cellular "architecture". Their sizes vary, they contain 90 - 300 nucleotides.
Ribonucleic acid is the main genetic material ina number of plant and animal viruses. Some RNA viruses never go through the reverse transcription of RNA to DNA. But still, many animal viruses, for example, retroviruses, are characterized by reverse translation of their RNA genome, directed by RNA-dependent reverse transcriptase (DNA polymerase) with the formation of a 2-stranded DNA copy. In most cases, the emerging 2-stranded DNA transcript is introduced into the genome, further providing the expression of viral genes and the production of new copies of RNA genomes (also viral).
Post-transcriptional modifications of ribonucleic acid
Its molecules synthesized with RNA polymerases are always functionally inactive and act as precursors, namely pre-RNA. They are transformed into already mature molecules only after they have passed the appropriate post-transcriptional modifications of RNA - the stages of its maturation.
Formation of mature mRNA begins during the synthesis of RNA and polymerase II at the stage of elongation. Already to the 5'-end of the gradually growing RNA strand is attached by the 5'-end of GTP, then the orthophosphate is cleaved off. Further, guanine is methylated with the appearance of 7-methyl-GTP. Such a special group, which is part of the mRNA, is called a "cap" (hat or cap).
Depending on the type of RNA (ribosomal, transport, template, etc.), precursors undergo various sequential modifications. For example, mRNA precursors undergo splicing, methylation, capping, polyadenylation, and sometimes editing.
Eukaryotes: totalfeature
The eukaryotic cell is the domain of living organisms, and it contains the nucleus. In addition to bacteria, archaea, any organisms are nuclear. Plants, fungi, animals, including the group of organisms called protists, are all eukaryotic organisms. They are both 1-celled and multicellular, but they all have a common plan of cellular structure. It is generally accepted that these organisms, so dissimilar, have the same origin, which is why the nuclear group is perceived as a monophyletic taxon of the highest rank.
Based on common hypotheses, eukaryotes originated 1.5 - 2 billion years ago. An important role in their evolution is given to symbiogenesis - the symbiosis of a eukaryotic cell that had a nucleus capable of phagocytosis and bacteria swallowed by it - precursors of plastids and mitochondria.
Prokaryotes: general characteristics
These are 1-celled living organisms that do not have a nucleus (formed), the rest of the membrane organelles (internal). The only large circular 2-stranded DNA molecule that contains most of the cellular genetic material is one that does not form a complex with histone proteins.
Prokaryotes include archaea and bacteria, including cyanobacteria. Descendants of non-nuclear cells - eukaryotic organelles - plastids, mitochondria. They are subdivided into 2 taxa within the domain rank: Archaea and Bacteria.
These cells do not have a nuclear envelope, DNA packaging occurs without the involvement of histones. The type of their nutrition is osmotrophic, and the genetic materialrepresented by one DNA molecule, which is closed in a ring, and there is only 1 replicon. Prokaryotes have organelles that have a membrane structure.
The difference between eukaryotes and prokaryotes
The fundamental feature of eukaryotic cells is associated with the presence of a genetic apparatus in them, 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, 2 nuclear phases are present in their life cycle. One has a haploid set of chromosomes, and subsequently merging, 2 haploid cells form a diploid cell, which already contains the 2nd set of chromosomes. It also happens that during subsequent division, the cell again becomes haploid. This kind of life cycle, as well as diploidy 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 reproduce by division. These structures are surrounded by a membrane. These organelles are plastids and mitochondria. In terms of vital activity and structure, they are surprisingly similar to bacteria. This circumstance prompted scientists to think that they are descendants of bacterial organisms that entered into symbiosis with eukaryotes.
Prokaryotes have few organelles, none of which is surrounded by a 2nd membrane. They lack the endoplasmic reticulum, the Golgi apparatus, and lysosomes.
Another important difference between eukaryotes and prokaryotes is the presence of the phenomenon of endocytosis in eukaryotes, including phagocytosis inmost groups. The latter is the ability to capture by means of confinement in a membrane bubble, and then digest various solid particles. This process provides the most important protective function in the body. The occurrence of phagocytosis is presumably due to the fact that their cells are of medium size. Prokaryotic organisms, on the other hand, are incommensurably smaller, which is why 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 arose among them.
Processing as one of the steps in protein biosynthesis
This is the second step that starts after transcription. Protein processing occurs only in eukaryotes. This is mRNA maturation. To be precise, this is the removal of regions that do not code for a protein, and the addition of controls.
Conclusion
This article describes what processing is (biology). It also tells what RNA is, lists its types and post-transcriptional modifications. The distinctive features of eukaryotes and prokaryotes are considered.
Finally, it is worth recalling that processing is the process of forming mature RNA from pre-RNA.
