Tài liệu, ebook Sinh Học

These are position- and orientation-independent DNA elements that stimulate or depress, respectively, transcription of associated genes Are often tissue-specific in that they rely on tissue-specific DNA-binding proteins for their activities Some DNA elements can act either as enhancer or silencer depending on what is bound to it

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E. coli glnA gene is an example of a prokaryotic gene depending on an enhancer for its transcription Enhancer binds the NtrC protein interacting wit polymerase bound to the promoter at least 70 bp away Hydrolysis of ATP by NtrC allows formation of an open promoter complex The two proteins interact by looping out the DNA Phage T4 late enhancer ...

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When lysogen suffers DNA damage, SOS response is induced Initial event is seen in a coprotease activity in RecA protein Repressors are caused to cut in half, removing them from l operators Lytic cycle is induced Progeny phage can escape potentially lethal damage occurring in host

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Region that binds to the ligand is an aptamer An expression platform is another module in the riboswitch which can be: Terminator Ribosome-binding site Another RNA element that affects gene expression Operates by depressing gene expression Some work at the transcriptional level Others can function at the translational level

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Compare the sedimentation of transcripts made in presence and absence of r Without r, transcripts cosedimented with the DNA template – they hadn’t been released With r present in the incubation, transcripts sedimented more slowly – they were not associated with the DNA template It appears that r serves to release the RNA transcripts from the DNA...

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Phenotype may not be obvious in the progeny, but still instructive Other cases can be lethal with the mice dying before birth Intermediate effects are also common and may require monitoring during the life of the mouse

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Bacterium infects plant, transfers Ti plasmid to host cells T-DNA integrates into the plant DNA causing abnormal proliferation of plant cells T-DNA genes direct the synthesis of unusual organic acids, opines which can serve as an energy source to the infecting bacteria but are useless to the plant

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Sickle cell disease is a genetic disorder The disease results from a single base change in the gene for b-globin Altered base causes insertion an incorrect amino acid into one position of the b-globin protein Altered protein results in distortion of red blood cells under low-oxygen conditions This disease illustrates that a change in a gene can...

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There is a rough correlation between DNA content and number of genes in a cell or virus This correlation breaks down in several cases of closely related organisms where the DNA content per haploid cell (C-value) varies widely C-value paradox is probably explained not by extra genes, but by extra noncoding DNA in some organisms

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Current research theories support the division of living organisms into three domains Bacteria Eukaryota Archaea living in the most inhospitable regions of the earth Thermophiles tolerate extremely high temperatures Halophiles tolerate very high salt concentrations Methanogens produce methane as a by-product of metabolism

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