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Gene Expression

Gene Expression. Open to Chapter 18. Dilemma. All the DNA in an organism’s cells is basically the same. We have many of the same genes as a fruit fly ( abt 60%). What accounts for the differentiation in the cells?. Which genes are expressed. Regulation of Gene Expression.

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Gene Expression

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  1. Gene Expression Open to Chapter 18

  2. Dilemma • All the DNA in an organism’s cells is basically the same. • We have many of the same genes as a fruit fly (abt 60%). • What accounts for the differentiation in the cells?

  3. Which genes are expressed.

  4. Regulation of Gene Expression • Regulation can occur at many levels in the DNA RNA PROTEIN • Transcription • Post-Transcription • Translation • Final Folding and Refolding of Proteins

  5. Overview • Prokaryotes have operons • Eukaryotes • Regulatory sequences • Selective transcription • Homeobox Genes (HOX) • Epigenome

  6. PROKARYOTE OPERON • Promotor- Where RNA polymerase attaches • Operator- switch that turns on or off. If repressor attaches, it is “off”. Transcription is disabled. • Gene • Examples: • Lac Operon- If Lactose is present, repressor inactive, gene turned on. • Trp Operon - If Tryptophan is present, repressor active, gene turned off.

  7. Figure 18.3b-1 DNA mRNA Protein Activerepressor Tryptophan (corepressor) (b) Tryptophan present, repressor active, operon off

  8. Lac and Trp Operons • No matter which type of operon, when the repressor is active, the gene is switched___. • When lactose is present, the gene is switched _____ • When tryptophan is present, the gene is switched ______

  9. Lac and Trp Operons • No matter which type of operon, when the repressor is active, the gene is switched off. • When lactose is present, the lac gene is switched on • When tryptophan is present, the trp gene is switched off

  10. EUKARYOTE REGULATORY SEQUENCES • Proteins (transcription factors) can bind to enhancer sequences on gene. Depending upon cellular conditions, this may enable gene to turn on (promote) or off (repress). Eukaryotes have multiple switches. • Induction- If proteins from neighboring cells are present, gene may turn on (ex: retina) • Hormones and other molecules may attach to enhancer sequence to turn on genes.

  11. Signal NUCLEUS PAGE 356 Chromatin Chromatin modification:DNA unpacking involvinghistone acetylation andDNA demethylation DNA Gene availablefor transcription Gene Transcription Exon RNA Primary transcript Intron RNA processing Tail mRNA in nucleus Cap Transport to cytoplasm CYTOPLASM mRNA in cytoplasm Translation Degradationof mRNA Polypeptide Protein processing, suchas cleavage and chemical modification Active protein Degradationof protein Transport to cellulardestination Cellular function (suchas enzymatic activity,structural support)

  12. EPIGENOME • Environmental effects can impact gene expression. • HistoneAcetylation- Adding acetyl group to histone proteins makes DNA more accessibile, promoting transcription • Methylation seems to prevent genes from loosening from histones, repressing transcription. • Twins can have different diseases, and their gene expression becomes more divergent as they age.

  13. HOMEOBOX GENES • HOX genes (Homeotic genes) • Master control genes • Segmented organisms have HOX genes associated with genes for body parts. For example, since the same genes form antenna and leg, the structure that forms depends upon its HOX master control gene.

  14. Normal Head Mutant Head

  15. Transcriptional control • Name and epigenetic factor that in represses transcription • Name an epigenetic factor that promotes transcription. • The reason that the same gene can code for either an antenna or a leg is that this gene is controlled by ______

  16. SELECTIVE TRANSCRIPTION • During transcription, intervening sequences of mRNA are removed (introns). • Exons are spliced together. • Males and females have the same set of genes, the fact that they are spliced differently accounts for the difference in gender. • Splicing and DNA rearrangement account for millions of different antibodies from the same genes.

  17. Post transcriptional ModificationRNAi • Interference RNA- RNAi • Regulates gene expression at transcription level, by attaching to complementary mRNA • Often inhibits or silences. • Forms may be called microRNA, or siRNA • See Video RNAi on Teachers Domain

  18. Hairpin Figure 18.15 Hydrogenbond miRNA Dicer 5 3 (a) Primary miRNA transcript miRNA miRNA-proteincomplex mRNA degraded Translation blocked (b) Generation and function of miRNAs

  19. See Controlling Protein Synthesis AP Boardworks, Slide 4-7

  20. 1 2 4 3 5 Figure 18.25 Cancer is a multistep process -Mutations of tumor suppressor - Mutation of proto-oncogene Colon Lossof tumor-suppressorgene APC(or other) Lossof tumor-suppressorgene p53 Activationof rasoncogene Additionalmutations Lossof tumor-suppressorgene DCC Colon wall Small benigngrowth(polyp) Largerbenign growth(adenoma) Normal colonepithelial cells Malignanttumor(carcinoma)

  21. See HMMI Click and Learn Genetic Switches • http://www.hhmi.org/biointeractive/gene-switch

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