Guide To Learn
The discovery of reverse transcriptase has modified the central dogma of molecular biology, which held that genetic information should pass only from DNA to RNA. This enzyme synthesizes DNA from RNA, thus showing that the information can flow from RNA to DNA. The enzyme was discovered by David Baltimore and Howard M. Temin in the […]
A large variety of inhibitors of RNA synthesis have been identified. The inhibitors fall into three groups. They are: Inhibitors Acting by Binding to DNA The best-known example of inhibitors that bind to DNA is actinomycin D, an antibiotic produced by Streptomyces antiboticus. The inhibition of RNA synthesis is caused by the insertion of its […]
The immediate products of transcription, the primary transcripts, are not necessarily biologically active. In order to make them as functional entities, many of them must be altered in several ways. These modifications are referred to as post-transcriptional modifications or processing, which include: mRNA Processing Prokaryotic mRNA In prokaryotes, most primary mRNA transcript functions in translation […]
The eukaryotic transcription is more complex than the prokaryotic transcription due to the cellular compartmentalization. The genetic material in eukaryotes is primarily localized in the nucleus. A nuclear membrane separates the nucleus from the cytoplasm, where the protein synthesis takes place. The promoters for different genes are different. Each promoter contains a combination of sites […]
Eukaryotic cells contain three different RNA polymerases, designated as I, II and III, which catalyse the transcription of genes encoding different classes of RNA. The subunit structure of yeast RNA polymerase is depicted in the following (Figure 4.11). Figure 4.11 Yeast RNA polymerases and their submits RNA Polymerase-I RNA polymerase-I (RNA Pol-I) is located in […]
Binding of RNA Polymerase RNA polymerase is sufficiently large enzyme that can come into contact with many DNA bases simultaneously. An estimate of the size of the region of the DNA where contact is made is obtained by selectively degrading adjacent DNA bases with DNase, a procedure known as ‘DNase protection method’. Figure 4.7 DNA […]
All genes of the genome are not transcribed at all the time. In higher eukaryotes (such as human beings) especially, where there is a tissue-specific gene expression (such as muscle, for example), there is selective transcription of the genome. Therefore, it would be a tremendous waste of a cell’s resources to transcribe unnecessary genes. Transcription […]
Sigma is a specificity factor. It directs RNA polymerase to the promoter and ensures that transcription is initiated only where it is supposed to be initiated. The very fact that RNA polymerase depends upon a specificity factor to direct the RNA polymerase to the correct promoter immediately offers a mechanism for controlling transcription. Different sigma factors […]
Bacterial and E. coli RNA polymerases are the best characterized RNA polymerases. There are about 13,000 RNA polymerase molecules present in an E. coli cell and the number varies with the growth conditions. Although not all the RNA polymerases are actually engaged in transcription at any one time, almost all are bound either specifically or non-specifically to DNA. The […]
RNA synthesis takes place within a ‘transcription bubble’ where the DNA is transiently separated into single strands. The unwinded template strand is used to direct the synthesis of the RNA strand. The RNA chain is synthesized from the 5′ → 3′ direction. That is, new nucleotides are added to the 3′-end of the growing chain. […]