Biologists call the term "transcription" a special stage of the implementation of hereditary information, the essence of which comes down to reading a gene and building a complementary RNA molecule to it. It is an enzymatic process involving the work of many enzymes and biological mediators. At the same time, most of the biocatalysts and mechanisms responsible for triggering gene replication are unknown to science. Because of this, it remains to be seen in detail what transcription is (in biology) at the molecular level.
Realization of genetic information
Modern science about transcription, as well as about the transmission of hereditary information, is not well known. Most of the data can be represented as a sequence of steps in protein biosynthesis, which makes it possible to understand the mechanism of gene expression. Protein synthesis is an example of the realization of hereditary information, since the gene encodes its primary structure. For every protein molecule, be it a structural protein, an enzyme, ormediator, there is a primary amino acid sequence recorded in the genes.
As soon as it becomes necessary to re-synthesize this protein, the process of "unpacking" the DNA and reading the code of the desired gene starts, after which transcription occurs. In biology, the scheme of such a process consists of three stages, conventionally identified: initiation, elongation, termination. However, it is not yet possible to create specific conditions for their observation during the experiment. These are rather theoretical calculations that allow a better understanding of the participation of enzyme systems in the process of copying a gene onto an RNA template. At its core, transcription is the process of RNA synthesis based on the despiralized 3'-5'-strand of DNA.
Transcription mechanism
You can understand what transcription is (in biology) using the example of messenger RNA synthesis. It begins with the "release" of the gene and the alignment of the structure of the DNA molecule. In the nucleus, hereditary information is located in condensed chromatin, and inactive genes are compactly “packed” into heterochromatin. Its despiralization allows the desired gene to be released and made available for reading. Then a special enzyme divides the double-stranded DNA into two strands, after which the 3'-5'-strand code is read.
From this moment, the transcription period itself begins. The enzyme DNA-dependent RNA polymerase assembles the starting section of RNA, to which the first nucleotide, complementary, is attached.3'-5'-strand of the DNA template region. Further, the RNA chain builds up, which lasts for several hours.
The importance of transcription in biology is given not only to the initiation of RNA synthesis, but also to its termination. Reaching the terminating region of the gene initiates the termination of reading and leads to the launch of an enzymatic process aimed at detaching the DNA-dependent RNA polymerase from the DNA molecule. The divided section of DNA is completely “crosslinked”. Also, during transcription, enzyme systems work that “check” the correctness of the addition of nucleotides and, if synthesis errors occur, “cut out” unnecessary sections. Understanding these processes allows us to answer the question of what is transcription in biology and how it is regulated.
Reverse transcription
Transcription is the basic universal mechanism for transferring genetic information from one carrier to another, for example from DNA to RNA, as it happens in eukaryotic cells. However, in some viruses, the sequence of gene transfer may be reversed, that is, the code is read from RNA to single-stranded DNA. This process is called reverse transcription, and it is appropriate to consider the example of human infection with the HIV virus.
The reverse transcription scheme looks like the introduction of a virus into the cell and the subsequent synthesis of DNA based on its RNA using the enzyme reverse transcriptase (revertase). This biocatalyst is initially present in the viral body and is activated when it enters the human cell. It allowssynthesize a DNA molecule with genetic information from nucleotides found in human cells. The result of the successful completion of reverse transcription is the production of a DNA molecule, which, through the integrase enzyme, is introduced into the DNA of the cell and modifies it.
The importance of transcription in genetic engineering
Importantly, this kind of reverse transcription in biology leads to three important conclusions. First, that viruses in phylogenetic terms should be much higher than single-celled life forms. Secondly, this is proof of the possibility of the existence of a stable single-stranded DNA molecule. Previously, there was an opinion that DNA can exist for a long time only in the form of a double-stranded structure.
Thirdly, since a virus does not need to have information about its genes to integrate into the DNA of cells of an infected organism, it can be proved that arbitrary genes can be introduced into the genetic code of any organism by reverse transcription. The latter conclusion allows the use of viruses as genetic engineering tools for embedding certain genes into the genome of bacteria.
