Introduction to Molecular Biology
Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman in Molecular Imaging in Oncology, 2008
Transcription is the process by which a DNA template is copied to form an mRNA by a RNA polymerase. This results in the transfer of the genetic information from DNA to RNA. This is the first step in gene expression. The transcription mechanism is situated in the nucleus of the cell. The resultant mRNA will be processed and transported into the cytoplasm for the translation process. A segment of DNA that is transcribed to form one molecule of RNA is called transcription unit. In most mammalian cells, it is estimated that only 1% of the DNA sequence will be transcribed into functional mRNA. The transcription process can be divided into three important steps: (i) initiation of RNA chain, (ii) elongation of the chain, and (iii) termination of the transcription that results in the transcript release.
Genetics and exercise: an introduction
Adam P. Sharples, James P. Morton, Henning Wackerhage in Molecular Exercise Physiology, 2022
Only one DNA strand of the double helix is transcribed into an RNA. Noncoding intron regions copied from the DNA are cut (spliced) out of the RNA and the exons fused together during its processing from “pre-RNA” to mature mRNA. Transcription begins at an initiation site along the DNA strand termed a promoter. Other regulatory DNA sequences are enhancer and silencer sequences. Enhancers are short DNA sequences that are activated when bound by proteins resulting in an increase in transcription (gene turned on). A gene sequence includes variable numbers of enhancers, and there is a relation between the number of activated enhancers and the rate of transcription and resultant amount of mRNA for that gene. In contrast, silencer sequences can bind repressor proteins that attenuate or suppress (silence) the transcription of a gene. Silencers just like enhancers are often located upstream of the gene-coding sequence, but they are also found downstream or far away from the gene. The latter can still impact the rate of transcription because the looping of the DNA within the nucleus brings the enhancer or silencer sites in close proximity to promoter(s).
Cellular and Molecular Basis of Human Biology
Lawrence S. Chan, William C. Tang in Engineering-Medicine, 2019
The human genome is consisted of 20,000 different genes and nucleic acids composed of 3 billion base pairs (Green et al. 2015). For the basic components of nucleic acid, the nucleotides, there are only 4 distinct nitrogenous bases: adenosine (short for A), thymine (T), guanine (G), and cytosine (C) and each nucleotide also contains a phosphate group and a sugar deoxyribose. One interesting and important fact is that virtually all differentiated cells have the identical and entire genome. Yet some proteins are produced by certain cell types and not by other cell types. The key factor is transcriptional factors, which function to bind to promoter region of DNA in initiating mRNA transcription. The binding of transcriptional factors enables the binding of RNA polymerase to DNA for the transcription. Activation and inactivation of certain transcriptional factors during human development determine the ability and inability to express certain proteins, and by extension their phenotype expressions, respectively (Hillis et al. 2014). Another interesting and also essential fact is that reactivation of cell-specific transcriptional factors could change a cell’s phenotype. For example, transgenic introduction of neuron-specific transcription factors into fibroblasts turn these connective tissue protein-producing cells into functional neurons with characteristic neuronal synapses (Hillis et al. 2014).
Targeting transcription factors in multiple myeloma: evolving therapeutic strategies
Published in Expert Opinion on Investigational Drugs, 2019
Shirong Li, Sonia Vallet, Antonio Sacco, Aldo Roccaro, Suzanne Lentzsch, Klaus Podar
Transcription is the first step of gene expression by which genetic information is copied from DNA to RNA by RNA polymerases. RNA molecules include mRNA, which serves as a template for protein synthesis through translation; as well as non-coding RNAs, rRNA, tRNA, siRNAs, miRNAs, lncRNAs and ribozymes in particular. Transcriptional programs warrant cell identity, division, growth, death, migration, and thereby organization of the organism (body plan) throughout life; and intermittently in response to extracellular signals including hormones, cytokines and growth factors. Transcription factors (TFs) are proteins that bind to the DNA helix at specific sequences (response elements: promoters; enhancers; and clustered enhancers, so-called super-enhancers (SE)) and thereby prompt (as activators) or block (as repressors) the recruitment and activity of RNA polymerases [1,2].
Epigenetic control of skin immunity
Published in Immunological Medicine, 2023
Human cells contain two meters of genomic DNA that is tightly folded and packed within the nucleus. Genomic DNA forms a secondary structure referred to as chromatin that fits into a limited space [7]. The basic unit of chromatin, the nucleosome, is consisted of 147 bp genomic DNA and a core histone octamer. DNA is negatively charged and histones are positively charged, and the opposing charges allow DNA to wrap itself tightly around the histone octamer to form a nucleosome. Initiation of transcription requires the binding of RNA polymerase II and several basic transcription factors, called TFIIA and TFIIB, bind to promoters located near the transcription start sites [8]. Sequence-specific DNA-binding transcription factors (TFs) are involved in the enhancement of transcription. TFs bind to enhancers and cause genomic DNA to form looped structures that shorten the distance between enhancers and promoters, thereby promoting the transcription of the target genes. Transcriptional activity is also closely related to the degree of DNA condensation associated with chromatin structure [6,8]. Tightly packed chromatin, called closed chromatin or heterochromatin, restricts the access of RNA polymerase II and the transcription factors to the regulatory sites, and consequently, suppresses the expression of target genes. Open chromatin or euchromatin that is less condensed allows easier access of the transcriptional machinery to DNA, thus setting target genes to be more actively transcribed.
Drug repurposing strategies and key challenges for COVID-19 management
Published in Journal of Drug Targeting, 2022
Shubham Mule, Ajit Singh, Khaled Greish, Amirhossein Sahebkar, Prashant Kesharwani, Rahul Shukla
The ssRNA released into the cell and protein synthesis is done via the host cell machinery with large polyproteins – polyprotein 1a and polyprotein 1ab are formed. Both of these polyproteins then proteolysed into a number of smaller proteins which form ‘replicase–transcriptase complex’ that is ultimately involved in the processes of replication and transcription. This replicase–transcriptase complex combines with viral RNA and lead to the replication of genomic RNA (+) and the formation of antisense genomic RNA (–). This antisense RNA has two fates. It can either be replicated back into the genomic RNA (+) or it can undergo discontinuous transcription. In the discontinuous transcription process, RNA (–) binds with RNA polymerases to initiate transcription at various sites. As a result of discontinuous transcription, the subgenomic mRNAs with different lengths encoding different viral encoded proteins are obtained. Viral proteins are then produced as a result of the translation of these subgenomic mRNAs.
Related Knowledge Centers
- Nucleic Acid
- Nucleotide
- Polymerase
- Primary Transcript
- Protein
- Messenger Rna
- NON-Coding Rna
- Base Pair
- Complementarity
- Antiparallel