Understanding the fundamental foundations of the existence of life is impossible without a clear understanding of the transmission of hereditary information and its implementation. The storage of the body's genes is realized through chromosomes, in which different sections of DNA are packaged, encoding the primary amino acid sequence of a certain protein. And the implementation of genetic information and its transmission by inheritance is achieved through its copying. This process is called "transcription". In biology, it means reading the code of a gene section and synthesizing a template for protein biosynthesis based on it.
Molecular basis of transcription
Transcription is an enzymatic process that is preceded by the "unpacking" of a DNA molecule and providing access for reading a specific gene. Then in the double-stranded DNA molecule onIn the initial section, hydrogen bonds between nucleotides are broken for 4 kadons. From this moment, the transcription initiation phase in biology begins, associated with the attachment of DNA-dependent RNA polymerase to the DNA macropolymer.
The natural outcome of initiation is the synthesis of the starting site of messenger RNA, and as soon as the first complementary nucleotide is attached to it and the translocation of DNA-dependent RNA polymerase occurs, one should speak of the beginning of the elongation stage. Its essence is reduced to the gradual movement of the DNA-dependent RNA polymerase along the DNA molecule in the 3`-5` direction, cutting the DNA hydrogen bonds in front and restoring them behind, as well as attaching a complementary nucleotide to the growing chain of the RNA template.
Enzyme DNA-dependent RNA polymerase catalyzes the addition of a nucleotide to RNA, while other enzyme systems are responsible for reading, separating hydrogen bonds and their reduction. All of them are located in the place where transcription takes place. Biology allows you to apply the method of labeled atoms and confirm the fact of their highest concentration in the nuclei of cells.
Transcription timeline
In laboratory conditions, the scientists of the research group "Human Genome" managed to artificially synthesize the DNA molecule itself and save the genetic code in it. This process took more than 2 decades, not counting the lengthy preparation. It is interesting how fast these processes proceed in a living cell. Main research methodtranslation and transcription - molecular biology. And although it is still experiencing difficulties associated with the impossibility of a visual demonstration of these processes, there is some evidence regarding the time of protein biosynthesis.
In particular, the process of "unpacking" genetic information can take 16-48 hours, and the transcription of the desired gene - about 4-8 hours. The synthesis of one small protein molecule based on messenger RNA will take about 4-24 hours, after which the stage of its “maturation” begins. This refers to the self-spontaneous packaging of a protein into a secondary and then into a tertiary structure. If the protein requires postsynthetic modification, then this process may take about a week or more.
Cellular structures, where transcription and translation occur, are being studied in more and more detail in biology. At the same time, it was possible to calculate that in eukaryotic cells with a large set of genetic material, the synthesis of a simple insulin molecule takes about 16 hours. Genetically modified Escherichia coli is able to synthesize such a molecule in 4 hours. In the case of large proteins of tertiary and quaternary structure, the process of their synthesis and final formation can take about 2 weeks.
Localization of transcription enzymes
Such a process as transcription (in biology) takes place in the place of direct storage of hereditary information. In eukaryotic cells, this is the cell nucleus, and in pre-nuclear life forms, it is the cytoplasm. viral enzymereverse transcriptase works in the nucleus of infected cells. At the same time, mitochondrial nucleic acids, which are a set of genes, also go through the transcription stage. In biology and genetics, the nature of these processes is still unknown.
But the fact of the presence of human mitochondrial diseases that are inherited by descendants confirms DNA replication, for which transcription is a necessary step. This means that such a process can take place in several cellular structures: in eukaryotes, these are mitochondria and the cell nucleus, and in prokaryotes, in the cytoplasm and plasmids.
Localization of biosynthetic processes
Locations where transcription and translation occur (in biology) are different, because the synthesis of protein molecules simply cannot occur in the cell nucleus. The assembly of the primary structure occurs on the ribosomal apparatus of the cell, which is predominantly concentrated in the cytoplasm on the membrane of the rough endoplasmic reticulum.
Synthesis in highly developed cells, which are characterized by a high rate of assembly of new protein molecules, occurs mainly on polyribosomes. But in bacterial and highly specialized cells, biosynthesis can proceed on disparate ribosomes in the cytoplasm. Viral bodies do not have their own synthetic apparatus and organelles, and therefore exploit the structures of infected cells.
