Chapter 18a - Chapter 18a 1 The tryptophan operon and the...

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Chapter 18a 1. The tryptophan operon and the lac operon 2. Mechanisms of regulation of gene expression in Euk. 3. Regulation of chromatin structure (methylation, acetylation, deacetylation) 4. Regulation of transcription initiation (transcription factors, enhancers, proximal/ distal control elements) 5. Post- transcriptional regulation (alternative splicing, miRNA, siRNA) 6. Regulation of translation initiation and post- translational regulation 7. Oncogenes and proto-oncogenes; genetic changes that affect the cell cycle 8. Factors that predispose individuals to cancer - Conducting the genetic orchestra o Both prok and euk: Must alter pattens in response to environmental changes o Multicellular euk must also dev + maintain multiple cell types Each cell type contains the same genome but expresses a different subset of genes. o Many roles played by RNA molecules in regulating euk gene expression - Bacteria often respond to environmental change by regulating transcription o Favored bacteria only express genes whose products are needed by cell If the environment is lacking in the amino acid tryptophan, (bacterium needs to survive), the cell responds by activating a metabolic pathway that makes tryptophan from another compound Latee if the human eats a tryptophan rich meal, the bacterial cell stops producing, saving itself from squandering resources. Bacteria tune their metabolism to changing environments o Metabolic control occurs on 2 levels: 1. Cells can adjust the activity of enzymes already present Relies on sensitivity of many enzymes to chemical cues that increase or decrease their catabolic activity o Note: the activity of the first enzyme in the tryptophan synthesis pathway is inhibited by the pathways end product If tryptophan accumulates in the cell, it shuts down the synthesis of more tryptophan by inhibiting enzyme activity o Such feedback inhibitors typical of anabolic pathways, allows a cell to adapt to short-term fluctuations in the supply of a substance it needs. 2. Cells can adjust the production level of certain enzymes; that is they can regulate the expression of the genes encoding the enzymes The action taken resulting from lack of enzyme, the control of enzyme prod. Occurs at the level of transcription, the synth of messengers RNA coding for these enzymes. Genes of bacterial genome are switched on and off by changes in the metabolic status of the cell.
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o The basic mechanism for this control of gene expression in bacteriam described as the operon model Discovered in 1961 by Francois Jacob and Jacques Monod - Controlling gene expression o Prok transcriptional level o In multicellular euk:
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Chapter 18a - Chapter 18a 1 The tryptophan operon and the...

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