BB lecture 11-18-09 gene regulation- eukaryotes

BB lecture 11-18-09 gene regulation- eukaryotes - Chapter...

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Chapter 18 (pp.355-366) Gene regulation ( continued ) Learning objectives: • Explain how catabolite activator protein ( CAP ) is a positive control for the lac operon For eukaryotic cells • Know the stages in gene expression that can be regulated in eukaryotic cells Explain how gene expression is regulated by chromatin methylation • Describe the role of control elements in transcription. • Distinguish between distal control elements and proximal control elements • Explain what is meant by coordinate gene expression
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Recall… Regulation of the trp and lac operons involves negative control of genes because operons are switched off by the active form of the repressor
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Positive Gene Regulation The lac operon is also subject to positive control through an stimulatory protein, called catabolite activator protein ( CAP ) When glucose is scarce, cAMP activates the CAP CAP binds to and activates the lac operon When glucose levels increase, cAMP levels drop , CAP detaches from the lac operon, turning it off
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Figure 18.5 Positive control of the lac operon by catabolite activator protein ( CAP ) Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesized. If glucose is scarce, the high level of cAMP activates CAP, and the lac operon produces large amounts of mRNA for the lactose pathway. [Analagous to a volume control] (a) CAP-binding site Operator Promoter RNA polymerase binds easily Inactive CAP Active CAP cAMP DNA Inactive lac repressor lacl lacZ
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(b) Lactose present, glucose present (cAMP level low): little lac mRNA synthesized. When glucose is present, cAMP is scarce, and CAP is unable to stimulate transcription. Inactive lac repressor Inactive CAP DNA RNA polymerase binds slowly Operator lacl lacZ CAP-binding site Promoter
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DNA RNA mRNA Protein I. Chromatin Structure &      Chemical Modification II. Transcription (most  common regulation site) III. RNA Processing (and  degradation) IV. Nuclear Export VI. Protein Modification       & degradation Overview:  Gene Expression Control Points (Eukaryotes) V. Translation cytoplasm nucleus
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Fig. 18-6 DNA Signal Gene NUCLEUS Chromatin modification Chromatin Gene available for transcription Exon Intron Tail RNA Cap RNA processing Primary transcript mRNA in nucleus Transport to cytoplasm mRNA in cytoplasm Translation CYTOPLASM Degradation of mRNA Protein processing Polypeptide Active protein Cellular function Transport to cellular destination Degradation of protein Transcription 1. Chromatin modification 1. Transcription 3. RNA processing 4. RNA degradation 5. Translation 6. Protein modification 7. Protein degradation
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Recall: Levels of chromatin packing 2 nm 10 nm DNA double helix Histone tails His- tones Linker DNA (“string”) (“bead”) Histone H1 (a) (10-nm fiber) Protein scaffold 30 nm 300 nm 700 nm 1,400 nm (b) 30-nm fiber (c) Looped domains (300-nm fiber) (d) Metaphase chromosome Loops Scaffold Nucleosome “beads” The tight packing of DNA restricts access & prevents transcription Heterochromatin = highly condensed, unable to transcribe Euchromatin = relaxed, areas open for transcription
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This note was uploaded on 01/20/2010 for the course BIO 50415 taught by Professor Batterton during the Spring '09 term at University of Texas.

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BB lecture 11-18-09 gene regulation- eukaryotes - Chapter...

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