Drag-and-Drop Protein Synthesis: Quiz - zeroBio
Further, the initiation of DNA synthesis in G,-PCC occurred significantly earlier than in the mononucleate G, cells.
Protein synthesis - Biology-Online Dictionary
AB - A mutant (dna-1) of Salmonella typhimurium defective in DNA synthesis is described. DNA synthesis is stopped in this mutant at 42° after a residual synthesis amounting to about 50 to 60% of the total cellular DNA in minimal medium and about 120 to 200% in a medium enriched with amino acids. Reshift back to permissive temperature after the inhibition of DNA synthesis at 42° allows for recovery of DNA synthesis after a lag of about 30 min. Protein synthesis is required during that lag for the recovery of DNA synthesis at permissive temperature. The density transfer experiments indicate that in the mutant dna-1 chromosome termini are replicated normally at 42° while the initiation of new rounds of replication is inhibited although the mutation is probably leaky at this temperature. The mutant is hypersensitive to sodium deoxycholate at 42° which suggests alteration of the membrane structure.
Different replicons of prokaryotes and eukaryotes utilize distinct mechanisms which vary in complexity, depending on the complexity of the organisms. A common feature of replication initiation control in E. coli genomes and plasmids is the presence of repeats of A^T rich sequences which facilitate unwinding of DNA and one or multiple repeats of a "dnaA box" to which the initiator DnaA protein in E. coli or its functional homolog (called Rep in other cases) binds to allow helical unwinding and primer synthesis. The level of DnaA protein regulates the initiation frequency and, in turn, is controlled at the level of transcription of the dnaA gene. Thus, there are complex negative autofeedback loops to control dnaA gene expression. DnaA regulates its own gene, and its steady-state level in the cell is determined by the cellular growth state. The frequency of replicon firing is dependent on the growth rate of the bacteria. As mentioned before, rapidly growing cells can have multiple copies of the genome, while cells with a very low growth rate have only one copy. Furthermore, as expected in cells with multiple genome copies, the genes near the origin will have a higher average copy number than the genes located near the terminus of replication and, therefore, will be more transcriptionally active.
Protein Synthesis -Translation and Regulation
The maintenance of genomic integrity in the form of the organism-specific nucleotide sequence of the genome is essential for preservation of the species during propagation. This requires an extremely high fidelity of DNA replication. Errors in RNA synthesis may be tolerated at a significantly higher level because RNAs have a limited half-life, even in nondividing cells, and are redundant. In contrast, any error in DNA sequence is perpetuated in the future, as there is only one or two copies of the genome per cell under most circumstances. Obviously, all organisms have a finite rate of mutation, which may be necessary for evolution. Genetic errors are one likely cause of such mutations. Inactivation of a vital protein function by mutation of its coding sequence will cause cell death. However, mutations that affect nonessential functions could be tolerated. Some of these mutations can still lead to change in the phenotype, which in extreme cases can cause pathological effects. In other cases, these may be responsible for susceptibility to diseases. In many cases, however, such mutations appear to be innocuous and are defined as an allelic polymorphism. The mammalian genome appears to have polymorphism in one out of several hundred base pairs. Such mutations obviously arose during the evolution and subsequent species propagation.
The error rate in replication of mammalian genome is about 10-6 to 10-7 per incorporated deoxynucleotide. The catalytic units of the replication machinery, namely, DNA polymerases, have a significantly higher error rate of the order of 10-4 to 10-5 per deoxynucleotide. In fact, some DNA polymerases, notably the reverse transcrip-tases of retroviruses, including HIV, the etiologic agent for AIDS, are highly error prone and incorporate a wrong nucleotide for every 102-103 nucleotides. These mistakes result in a high frequency of mutation in the viral protein, which helps the virus escape from immunosurveil-lance. The overall fidelity of DNA replication is significantly enhanced by several additional means. The editing or proof-reading function of the replication machinery is a 3′ ^ 5′ exonuclease (which is either an intrinsic activity of the core DNA polymerase or is present in another subunit protein of the replication complex) which tests for base pair mismatch during DNA replication and removes the misincorporated base. Such an editing function is also present during RNA synthesis. In addition, after replication is completed, the nascent duplex is scanned for the presence of mispaired bases. Once such mispairs are marked by mismatch recognition proteins, a complex mismatch repair process is initiated, which causes removal of a stretch of the newly synthesized strand spanning the mismatch, followed by resynthesis of the segment, as described later.
Origins and complexes: the initiation of DNA replication ..
AB - The origin of replication of the broad host-range plasmid R1162 contains two, oppositely facing initiation sites for DNA synthesis. Either of these sites can be deleted from an R1162 plasmid derivative. However, the resulting plasmids are unstable, maintained at a lower copy-number in the cell, and form dimers and other recombinants that are required for propagation of the plasmid. In vitro, a derivative lacking one initiation site is deficient in synthesis of the strand normally initiated from that site. The properties of the intact origin are restored if it contains two oppositely facing sites; one initiation site may substitute for the other, and each site need not be in its original orientation. Overall, the results suggest that synthesis of each strand of R1162 DNA is initiated at a single site, and that there is no efficient system for initiation of lagging strand synthesis during transit of the replication forks.
A mutant (dna-1) of Salmonella typhimurium defective in DNA synthesis is described. DNA synthesis is stopped in this mutant at 42° after a residual synthesis amounting to about 50 to 60% of the total cellular DNA in minimal medium and about 120 to 200% in a medium enriched with amino acids. Reshift back to permissive temperature after the inhibition of DNA synthesis at 42° allows for recovery of DNA synthesis after a lag of about 30 min. Protein synthesis is required during that lag for the recovery of DNA synthesis at permissive temperature. The density transfer experiments indicate that in the mutant dna-1 chromosome termini are replicated normally at 42° while the initiation of new rounds of replication is inhibited although the mutation is probably leaky at this temperature. The mutant is hypersensitive to sodium deoxycholate at 42° which suggests alteration of the membrane structure.
DNA synthesis in prokaryotes Flashcards | Quizlet
Proteins of DNA Replication DNA exists ..
T1 - Reversible arrest of haploid yeast cells at the initiation of DNA synthesis by a diffusible sex factor
Protein Synthesis - Elmhurst College
Synthesis of RNA exhibits several features that are synonymous with DNA replication
Initiation and control of DNA synthesis. — University of Utah
Teaching Protein Synthesis (Replication, Transcription, and Translation) is a challenge
T1 - Initiation and control of DNA synthesis
Unlike the genomes in bacteria and plasmids (as well as in mitochondria and chloroplasts) which consist of a circular duplex DNA, with a single ori sequence, the genomes of eukaryotes are not only much larger and linear, but also contain multiple ori sequences for DNA replication and thus multiple replicons. Thousands ofreplicons are simultaneously fired in mammalian genomes, as is needed to complete replication of the genome in a few hours. Mammalian genomes are three orders of magnitudes larger than the E. coli genome for which one round of replication requires about 40 min at 37°C. Replication of a mammalian genome, initiated at a single ori, would thus take more than 1 week with the same rate of synthesis. In fact, it would be even longer because the rate of DNA chain elongation is slower in eukaryotes than in E. coli, possibly because of the increased complexity of eukaryotic chromatin.
TRANSLATION INITIATION (Protein Synthesis) - what-when-how
As mentioned earlier, DNA replication in eukaryotes occurs only during the S phase, which can last for several hours but whose duration varies with the organism, the cell type, and also the developmental stage. For example, in a rapidly growing early embryo of the fruitfly D. melanogaster, cellular multiplication with duplication of the complete genome occurs in less than 15 min. The details of temporal regulation of firing of different repli-cons are not known. However, euchromatin regions are replicated earlier than the heterochromatin regions.
Initiation of Protein Synthesis in Bacteria
Much of the information about the composition of the E. coli Pol III holoenzyme, and DNA chain elongation, was generated from studies of the replication of small, single-stranded circular DNAs of bacterial viruses 0X174 and M13 and also of laboratory-constructed plasmid DNA containing the ori (ori C) of E. coli. Asymmetric dimeric replication complexes have also been identified for larger E. coli viruses such as T4 with a linear genome and for the mammalian SV40 virus with a double-strand circular genome. In circular genomes, DNA synthesis is terminated at around 180° from the origin. In the case of linear genomes, termination occurs halfway between two neighboring replicons. The mechanism of termination is not completely understood. Although, in the E. coli genome, specific termination (ter) sequences are present, which bind to terminator proteins, such proteins act as anti-helicases to prevent strand separation. However, the termination may not be precise and occurs when the replicating forks collide.
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