Lecture 9 - 5:25 - Lecture 9: Wednesday, May 25, 2011...

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Unformatted text preview: Lecture 9: Wednesday, May 25, 2011 Biology 172 Todays Outline Announcements Chromosomal Mutations Bacterial Gene Expression- Overview-Lac operon- Monods expt- Operons- Negative Regulation- Catabolite Repression Discussion Tomorrow; Lac Operon Quiz : second half of Mondays lecture and all of todays lecture Chromosome-Level Mutations Mutations can involve larger-scale changes in the composition of chromosomes. Polyploidy is a change in the number of each type of chromosome present. Aneuploidy is the addition or deletion of a chromosome. Chromosomal Mutations changes affecting large segments of DNA or entire chromosomes 1. Alterations in Chromosome Number- caused by abnormal chromosome separation during cell division Example: Trisomy 21 in humans causes Down syndrome 2. Alterations in Parts of Chromosomes- caused by recombination errors or chromosome breakage Minor normal translocated Chromosome level Mutations Inversion Duplication Deletion Translocation Chromosome-Level Mutations Composition of individual chromosomes can change. Inversion occurs when a chromosomal segment detaches, flips, and reattaches to the chromosome. Chromosomal translocation occurs when a chromosomal segment detaches and becomes attached to a different chromosome. 2. Alterations in Parts of Chromosomes- caused by recombination errors or chromosome breakage Impact on Organism Major Major Minor Minor (until next generation!) Chromosomal mutations play an important role in the evolution of genomes and species Example: Differences between human and mouse chromosomes can be explained by translocations Control gene expression at these levels DNA RNA Protein Replication Transcription Translation Protein* Post-translation Gene Expression Bacterial Gene Expression Gene Expression Regulating the amount of active gene product (protein) by: Control of gene expression at the level of transcription Control of at the level of translation Post-translational control The Importance of Regulation Isnt having the gene the important thing? yes, but controlling its function is also critical consider a light bulb or an orchestra What about a real case? alternative energy sources for E. coli need different transport proteins and different processing enzymes for each one why not have them all available all the time? The Importance of Regulation Regulation minimizes interference and maximizes efficiency intestinal bacteria compete with other bacteria and with host cells for nutrients bacteria cant put 20 different sugar transport proteins in their membrane either will be too few of a given type to bring in the sugar quickly or will be so many proteins that they will get in each others way bacteria also cant maintain 20 different sets of processing enzymes there may be cross-reactivity (processing by wrong enzymes) but theres also the energetic cost of making so many (unneeded) proteins Natural selection is ruthless about efficiency...
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Lecture 9 - 5:25 - Lecture 9: Wednesday, May 25, 2011...

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