Biologists call the term “transcription” a special stage in the implementation of hereditary information, the essence of which is to read the gene and build an RNA molecule complementary to it. This is an enzymatic process associated with the work of many enzymes and biological intermediaries. However, most of the biocatalysts and mechanisms responsible for triggering gene replication are unknown to science. Because of this, it remains to be understood in detail what transcription (in biology) is at the molecular level.
Implementation of genetic information
The modern science of transcription, as well as the transmission of hereditary information, is not well known. Most of the data can be represented as a sequence of stages of protein biosynthesis, which allows us to understand the mechanism of gene expression. Protein synthesis is an example of the implementation of hereditary information, since the gene encodes exactly its primary structure. For each protein molecule, whether it is a structural protein, enzyme or mediator, there exists a primary amino acid sequence recorded in the genes.
As soon as there is a need 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, allocated conditionally: 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 matrix. In essence, transcription refers to the process of RNA synthesis based on the despiralized 3'-5'-DNA strand.
Transcription mechanism
It is possible to analyze what transcription is (in biology) using the synthesis of information RNA as an example. 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 you to free the desired gene and make it readable. Then, a special enzyme divides the double-stranded DNA into two chains, after which the code of the 3'-5'-chain is read.
From this moment, the transcription period itself begins. The DNA-dependent RNA polymerase enzyme assembles the RNA start region, to which the first nucleotide complementary to the 3'-5'-chain of the DNA template region joins. Next, the RNA chain grows, which lasts several hours.
The importance of transcription in biology is given not only in the initiation of RNA synthesis, but also in its termination. Reaching the terminating region of the gene initiates the termination of reading and leads to the start of the enzymatic process aimed at disconnecting the DNA-dependent RNA polymerase from the DNA molecule. In this case, the separated DNA region is completely “crosslinked”. Also, during the transcription, enzyme systems work that “check” the correct attachment of nucleotides and, when synthesis errors occur, “cut out” unnecessary sections. Understanding these processes allows us to answer the question of what transcription is 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 occurs in eukaryotic cells. However, for some viruses, the sequence of gene transfer may be reverse, 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 the 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 allows you to synthesize 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
It is important that such transcription in biology, which proceeds in the opposite direction, allows us to draw three important conclusions. First, that viruses in phylogenetic terms should be much higher than unicellular life forms. Secondly, this is evidence of the existence of a stable single-stranded DNA molecule. Previously, it was believed that DNA can exist for a long time only in the form of a double-stranded structure.
Thirdly, since the virus does not need to have information about its genes in order to incorporate the cells of an infected organism into the DNA, 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 in the bacterial genome.