In vivo synthesis of a polycistronic messenger RNA for …
Chain elongation proceeds in the 5'--> 3' direction, and the"transcription bubble" (the length of "melted" DNA) travelswith the RNA polymerase. As a consequence, the unmelted DNA is overwound infront of the bubble and underwound behind the bubble. Topoisomerases then act torelax the positive and negative supercoils. The mRNA that is produced ishybridized for a short length to the DNA at the downstream position, and existsseparate from the DNA as a "tail", the point of attachment being atthe downstream end. The RNA polymerase does not fall off of the DNA as it isprocessing because of its relatively tight, but nonspecific, binding on bothsides of the transcription bubble, stabilized by its "thumb" wrapping around the DNA. About 20 to 50 nucleotides are transcribed per secondat 37 C and one nucleotide is incorrectly transcribed in about every 104 . As genes are repeatedly transcribed, this error rate is not too deleterious,especially when coupled with the fact that there are multiple codons("synonyms") for each amino acid subsequently translated and thatsingle amino acid substitution errors in a protein usually do not hinder itsfunction.
Monocistronic mRNA - definition of Monocistronic mRNA …
Different mRNAs within the same cell have distinct lifetimes(stabilities). In bacterial cells, individual mRNAs can survivefrom seconds to more than an hour; in mammalian cells, mRNAlifetimes range from several minutes to days. The greater thestability of an mRNA, the more protein may be produced from thatmRNA. The limited lifetime of mRNA enables a cell to alter proteinsynthesis rapidly in response to its changing needs. There are manymechanisms that lead to the destruction of a message, some of whichare described below.
Ribosomal RNA (rRNA) constitutes about 95% of all RNA and about 67% of theRNA in ribosomes. The remainder of RNA includes transfer RNA (tRNA), messengerRNA (mRNA) and other types present in smaller amounts, like "smallnuclear" RNAs (snRNAs) involved in mRNA splicing and "guide" RNAs that are involved in editing of RNA. These latter two processes occur in thepost-translation stage of the life cycle of eukaryotic mRNA. All RNAs are codedfor by DNA, and the different types of RNA polymerase in eukaryotes reflect thisand the fact that, in eukaryotes, translation of mRNA into DNA occurs outside ofthe nucleus.
Detection of in vivo synthesis of polycistronic mRNAs …
14.2 Interactions of Animal Viruses and Their Hosts Step 5: Nucleic acid replication and protein synthesis RNA viruses Some RNA virus genomes act as a mRNA (”plus-strand” viruses) All others (minus-strand viruses) possess a prepackaged, virus-encoded RNA-dependent RNA polymerase DNA viruses encode RNA polymerases Many viruses have polycistronic mRNAs Viral polypeptides are synthesized by the cell’s translational machinery
What is the role of messenger RNA and ribosomes in protein synthesis
(i) When tryptophan is present in nutrient medium. One more type of control system of the trp operon occurs post-transcriptionally (after the start of transcription process) that is based on the synthesis of a leader polypeptide when tryptophan is present in the external medium. A 162 base pair long DNA found at the 5′ end of the gene trp E (part or gene E), having two successive tryptophan codons, is responsible for the synthesis of leader polypeptide. This regulation is based on the coupling of transcription and translation processes in prokaryotes. After the initiation of transcription, ribosomes one by one get attached to the 5′ end of the newly synthesizing mRNA and start the synthesis of the respective proteins. In the presence of tryptophan, the two tryptophan codons are translated due to the availability of tryptophan in external medium, thus, forming the complete leader polypeptide. This leader polypeptide induces the formation of hairpin loop in the newly synthesizing mRNA, causing the detachment of RNA polymerase from the coding strand of DNA. Thus, termination of further transcription occur (Fig. 11.9).
Definition of polycistronic in the English dictionary
Precursors of most rRNA are synthesized in nucleoli with the enzyme RNApolymerase I. Precursors of mRNA are synthesized in the nucleoplasm by RNApolymerase II while RNA polymerase III, also in the nucleoplasm, synthesizesprecursors of 5S RNA, tRNAs and other RNAs found both in the nucleus andcytoplasm. Mitochondria have their own RNA polymerases, and these are analogousto chloroplast RNAs found in plants. We will focus on RNA polymerase II as it isthe one involved in transcription in eukaryotes.
15/10/2012 · Polycistronic mRNA includes coding ..
14.2 Interactions of Animal Viruses and Their Hosts Viruses tend to be species- and cell-specific Infection is a 9-step process Attachment Entry Targeting to site of viral replication Uncoating Nucleic acid replication and protein synthesis Maturation Release from cells Shedding from host Transmission to other hosts