Short interspersed nuclear elements SINEs 2 nd most abundant o SINEs are

Short interspersed nuclear elements sines 2 nd most

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Short interspersed nuclear elements (SINEs) – 2 nd most abundant o SINEs are usually less than 400 bp long, do not encode proteins o The reverse transcriptase required for SINE transposition is provided by a LINE-type element The genetic + evolutionary significance of transposable elements o Transposable genetic elements are powerful mutagens + play major roles in the evolution of living organisms o Crossing over may occur between homologous transposons located at different positions on the same/or different chromosomes o These are referred to as ectopic intra/inter-chromosomal exchanges Beneficial uses of transposable elements in molecular genetics o Transposons are used in genetic research to induce mutations – “sleeping beauty” mutation o Transposons are used as vector to move DNA within genomes o Crossing over between paired transposons can create chromosomal rearrangements o Intra-chromosomal recombination between transposons in the same orientation produces a deletion o Unequal crossing over between transposons on sister chromatids produces a gene duplication Chapter 18: Gene regulation in Prokaryotes o Transcription is the most important step of gene regulation in prokaryotes o A bacterium often finds itself in an ever changing environment o Genetic regulation in bacteria is primarily focused on adaptation to this ever changing environment they are in o Genes whose products are not required are in general not expressed – unless environmental conditions change in a way that makes their expression useful Constitutively expressed genes: o Products of certain genes (tRNAs, rRNAs, ribosomal proteins, subunits of RNA polymerase, other enzymes involved in housekeeping functions are essential components of all living cells o Gene products are required at all times – always on
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o These genes are continuously expressed in most cells = constitutive expression Inducible + repressible genes: o Some gene products are needed for cell growth only under certain environmental conditions o Regulatory mechanisms allow the expression of these gene products only when they are needed = inducible/repressible genes Induction of expression of genes for lactose utilization o Glucose is a preferred carbon source for many bacteria, but can use other carbon sources if glucose is absent o For utilization of lactose, gene expression is induced when lactose is present and glucose is absent o Induction occurs at the level of transcription + alters the rate of translation of lactose-utilization enzymes o Enzymes involved in catabolic (breakdown) pathways are often inducible Repression of genes for tryptophan biosynthesis o Genes are expressed (or de-repressed) in the absense of tryptophan and turned off (repressed) when tryptophan is available o Repression occurs at the level of transcription of genes involved in tryptophann biosynthesis o Enzymes involved in anabolic (biosynthesis) pathways are often repressible Regulation of inducible systems * all depends on binding complex
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