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Homework #2 is due 10/17 Bonus #1 is due 10/24 Exam key is online Office hours: M 10/8 10-11:30am 2-5pm in Bio 6
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Fig 16.1 Gene Expression is controlled at all of these steps: DNA packaging Transcription RNA processing and transport RNA degradation Translation Post-translational
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Eukaryotic transcription must be activated by binding of transcription factors
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Enhancers are regulatory regions located some distance away from the promoter
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Proteins that help bend DNA can play an important role in transcription Fig 11.14
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DNA bends to bring different areas in to close contact.
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Enhancer-blocking insulators prevent enhancer activation Fig 11.17
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Fig 11.18 Insulators block the folding of DNA preventing enhancers from interacting with the promoter
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How do eukaryotic cells jointly express several proteins (without operons)?
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Promoter sequences where transcription factors can bind activating multiple gene in response to the environment
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Fig 11.16 Combinations of regulatory transcription factors regulate expression of different genes
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Promoters typically have several regulatory sequences
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Steroid response element
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Steroids bind to receptors/transcription factors inside cell get translocated to the nucleus bind to promoters and activate transcription. cytoplasm
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Steroid response element
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Fig 16.1 Gene Expression is controlled at all of these steps: DNA packaging Transcription RNA processing and transport RNA degradation Translation Post-translational
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Fig 12.23 Alternate Splicing in Drosophila sex determination
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Fig 12.23 Alternate splicing leads to sex determination in fruit flies
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Mammalian mRNA Splice-Isoform Selection Is Tightly Controlled Jennifer L. Chisa and David T. Burke Genetics, Vol. 175: 1079-1087, March 2007 Regulation of gene expression is often in response to a changing environment. But how stable can alternative splicing be, and does it play a role in maintaining homeostasis?
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Alternative splicing modifies at least half of all primary mRNA transcripts in mammals. More than one alternative splice isoform can be maintained concurrently in the steady state mRNA pool of a single tissue or cell type, and changes in the ratios of isoforms have been associated with physiological variation and susceptibility to disease. Splice isoforms with opposing functions can be generated; for example, different isoforms of Bcl-x have pro-apoptotic and anti-apoptotic function. Chisa, J. L. et al. Genetics 2007;175:1079-1087 Fig. 1
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Using RT-PCR alternatively spliced versions of different genes were identified
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Chisa, J. L. et al. Genetics 2007;175:1079-1087 Fig. 4 variation in splice-isoform ratios is conserved in two genetically diverse mouse populations Black= genetically heterogeneous population UMHET3 Red= a population of hybrid females
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Chisa, J. L. et al. Genetics 2007;175:1079-1087 Fig. 5 In different individuals splice isoforms in different tissues are conserved
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Chisa, J. L. et al. Genetics 2007;175:1079-1087 Fig. 6 Splice-isoform ratios differ between young and old animals (different environments)
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Conclusions: Differences are observed in different tissues and at different ages, but there was always tight control of the relative amounts of the different splice-isoforms. Slight differences in alternative splicing may be indicative of abnormalities (disease).
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