In this article, we will discuss about the transcription of DNA (synthesis of messenger RNA from DNA). The process of transcription is regulated by DNA-dependent RNA polymerase. One of the two strands of DNA acts as the coding strand and is identical to the single-stranded RNA. The other strand acts as the non-coding strand, complementary to RNA, and acts as a template for the synthesis of mRNA. The process includes four steps that lead to the formation of mRNA. Binding of the activator with the template must be of high affinity. If the sigma factor is not present, or the initiator binds with another region instead of the recognized template, no transcription will take place.
The process of transcription is a fundamental mechanism that allows the genetic information encoded in DNA to be converted into functional molecules, such as proteins. This intricate process involves the synthesis of RNA molecules based on the DNA template, enabling the expression of genes and the subsequent functioning of living organisms. In this article, we will explore the transcription process, its significance, and the key players involved, supported by relevant references. https://www.nature.com/scitable/topicpage/dna-transcription-426
MECHANISM OF TRANSCRIPTION:
Transcription is a highly regulated process that occurs in the nucleus of eukaryotic cells and the cytoplasm of prokaryotes. It involves four main stages: template recognition, initiation, elongation, and termination.
1. TEMPLATE REGULATION:
In this step, RNA polymerase recognizes the template and binds with it. If the binding is of high affinity, then melting starts at the -10 region of the template. As a result, the double-stranded DNA converts into two single-stranded molecules. The process of binding and melting is crucial for the proper functioning of RNA polymerase. It allows the enzyme to initiate transcription and synthesize an RNA molecule based on the template strand. This recognition and binding event is a fundamental step in gene expression and plays a vital role in the regulation of genetic information.
During initiation, RNA polymerase, the enzyme responsible for the process of transcription, recognizes and binds to specific DNA sequences called promoters. This crucial binding event serves as the initial point from which transcription commences. The process entails the RNA polymerase accurately identifying the promoters, which act as recognition signals on the DNA molecule, guiding the polymerase to the appropriate starting point for transcription.
Elongation follows, where RNA polymerase synthesizes an RNA molecule complementary to the DNA template strand. Several elongation factors are involved in this process, which elongate the template and add nucleotides. During elongation, the RNA polymerase moves along the DNA template, unwinding the double helix and forming a single-stranded RNA molecule. As the RNA polymerase moves along, it adds ribonucleotides to the growing RNA chain, based on the complementary base pairing between the template strand and the incoming ribonucleotides. This elongation process continues until the RNA polymerase reaches a termination sequence, at which point it dissociates from the DNA template and releases the completed RNA molecule.
Finally, termination occurs when RNA polymerase reaches a termination sequence, resulting in the release of the newly synthesized RNA molecule. It involves two mechanisms, Rho dependent and Rho independent termination. In first mechanism, the protein complex recognize the stop codon and bind with it to terminate the transcription of DNA. In second mechanism, GC base pairs followed by U and A residues bind with stop codon and displace the transcribed chain. So termination occur.
RNA POLYMERASE-TRANSCRIPTION OF DNA:
RNA polymerase is the key enzyme involved in transcription. In prokaryotes, a single RNA polymerase synthesizes all types of RNA molecules. However, in eukaryotes, three distinct RNA polymerases (I, II, and III) are responsible for transcribing different classes of RNA. RNA polymerase II is primarily involved in transcribing protein-coding genes, making it a crucial player in gene expression.
PROMOTERS AND TRANSCRIPTION FACTORS:
Promoters are specific DNA sequences located upstream of the gene that provide binding sites for RNA polymerase and other proteins called transcription factors. Transcription factors play a vital role in regulating gene expression by facilitating or inhibiting the binding of RNA polymerase to the promoter. They ensure precise control over which genes are transcribed and when, allowing cells to respond to various internal and external signals.
TRANSCRIPTION AND GENE REGULATION:
Transcription plays a crucial role in gene regulation, determining which genes are expressed and to what extent. The presence or absence of specific transcription factors and other regulatory proteins can influence the binding of RNA polymerase to the promoter, thereby modulating gene expression. Dysregulation of transcriptional processes can lead to various diseases, including cancer and genetic disorders.
Transcription is a complex and highly regulated process that allows the genetic information stored in DNA to be transcribed into functional RNA molecules. This process is essential for gene expression and plays a crucial role in the regulation of various biological processes. Understanding the intricacies of transcription provides valuable insights into the functioning of living organisms and has significant implications in fields such as medicine and biotechnology.
Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2002). Molecular Biology of the Cell (4th ed.). Garland Science.
Lodish, H., Berk, A., Zipursky, S. L., Matsudaira, P., Baltimore, D., & Darnell, J. (2000). Molecular Cell Biology (4th ed.). W. H. Freeman and Company.
Roeder, R. G. (1996). The role of general initiation factors in transcription by RNA polymerase II. Trends in Biochemical Sciences, 21(9), 327-335. https://www.scirp.org/(S(351jmbntvnsjt1aadkozje))/reference/referencespapers.aspx?referenceid=772533
Ptashne, M., & Gann, A. (1997). Transcriptional activation by recruitment. Nature, 386(6625), 569-577.
Levine, M., & Tjian, R. (2003). Transcription regulation and animal diversity. Nature, 424(6945), 147-151.