AP-Biology-Chapter-1 - Chapter 18 Bacterial Genetics AP Biology 2005-2006 Why study bacterial genetics  Its an easy place to start history  we

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Unformatted text preview: Chapter 18. Bacterial Genetics AP Biology 2005-2006 Why study bacterial genetics?  Its an easy place to start history  we know more about it   systems better understood simpler genome  good model for control of genes   build concepts from there to eukaryotes  bacterial genetic systems are exploited in biotechnology 2005-2006 AP Biology Bacteria  Bacteria review one-celled organisms  prokaryotes  reproduce by mitosis   binary fission generation every ~20 minutes 108 (100 million) colony overnight!  rapid growth   dominant form of life on Earth  incredibly diverse  AP Biology 2005-2006 Bacterial diversity rods and spheres and spirals« Oh My! AP Biology 2005-2006 Bacterial diversity Borrelia burgdorferi Treponema pallidum Lyme disease Syphillis Escherichia coli O157:H7 AP Biology Hemorrhagic E. coli Enterococcus faecium skin infections 2005-2006 Bacterial genome  Single circular chromosome haploid  naked DNA   no histone proteins ~4300 genes 1/1000 DNA in eukaryote  ~4 million base pairs   Intro to Bacteria video AP Biology 2005-2006 No nucleus!  No nuclear membrane chromosome in cytoplasm  transcription & translation are coupled together   no processing of mRNA no introns  but Central Dogma still applies   use same genetic code 2005-2006 AP Biology Binary fission   Replication of bacterial chromosome Asexual reproduction   offspring genetically identical to parent where does variation come from? AP Biology 2005-2006 Variation in bacteria  Sources of variation spontaneous mutation  transformation    bacteria shedding DNA plasmids DNA fragments transduction  conjugation  transposons  AP Biology 2005-2006 Spontaneous mutation   Spontaneous mutation is a significant source of variation in rapidly reproducing species Example: E. coli    human colon (large intestines) 2 x 1010 (billion) new E. coli each day! spontaneous mutations    for 1 gene, only ~1 mutation in 10 million replications each day, ~2,000 bacteria develop mutation in that gene but consider all 4300 genes, then: 4300 x 2000 = 9 million mutations per day per human host! 2005-2006 AP Biology Transformation  Bacteria are opportunists  pick up naked foreign DNA wherever it may be hanging out  have surface transport proteins that are specialized for the uptake of naked DNA import bits of chromosomes from other bacteria  incorporate the DNA bits into their own chromosome    express new gene form of recombination 2005-2006 AP Biology Swapping DNA  Genetic recombination by trading DNA 1 3 2 arg+ trp- argtrp+ minimal media AP Biology 2005-2006 Plasmids  Plasmids  small supplemental circles of DNA   5000 - 20,000 base pairs self-replicating 2-30 genes bacterial sex!! rapid evolution antibiotic resistance  carry extra genes   can be exchanged between bacteria     can be imported from environment 2005-2006 AP Biology Plasmids This will be important! AP Biology 2005-2006 Plasmids & antibiotic resistance  Resistance is futile?    1st recognized in 1950s in Japan bacterial dysentery not responding to antibiotics worldwide problem now  resistant genes are on plasmids that are swapped between bacteria Resistance in Bacteria video AP Biology 2005-2006 Biotechnology  Used to insert new genes into bacteria  example: pUC18  engineered plasmid used in biotech AP Biology antibiotic resistance gene on plasmid is used as a selective agent 2005-2006 Transduction Phage viruses carry bacterial genes from one host to another AP Biology 2005-2006 Conjugation  Direct transfer of DNA between 2 bacterial cells that are temporarily joined  results from presence of F plasmid with F factor  F for ³fertility´ DNA   E. coli ³male´ extends sex pilli, attaches to female bacterium cytoplasmic bridge allows transfer of DNA AP Biology 2005-2006 Any Questions?? AP Biology 2005-2006 Bacterial Genetics Regulation of Gene Expression AP Biology 2005-2006 Bacterial metabolism  Bacteria need to respond quickly to changes in their environment  if have enough of a product, need to stop production   why? waste of energy to produce more how? stop production of synthesis enzymes  if find new food/energy source, need to utilize it quickly   why? metabolism, growth, reproduction how? start production of digestive enzymes 2005-2006 AP Biology Reminder: Regulation of metabolism  Feedback inhibition  product acts as an allosteric inhibitor of 1st enzyme in tryptophan pathway AP Biology - = inhibition 2005-2006 Another way to Regulate metabolism  Gene regulation  block transcription of genes for all enzymes in tryptophan pathway  saves energy by not wasting it on unnecessary protein synthesis AP Biology - = inhibition 2005-2006 Gene regulation in bacteria   Control of gene expression enables individual bacteria to adjust their metabolism to environmental change Cells vary amount of specific enzymes by regulating gene transcription  turn genes on or turn genes off  ex. if you have enough tryptophan in your cell then you don¶t need to make enzymes used to build tryptophan  waste of energy  turn off genes which codes for enzymes 2005-2006 AP Biology So how can genes be turned off?  First step in protein production? transcription  stop RNA polymerase!   Repressor protein  binds to DNA near promoter region blocking RNA polymerase   binds to operator site on DNA blocks transcription AP Biology 2005-2006 Genes grouped together  Operon  genes grouped together with related functions  ex. enzymes in a synthesis pathway single promoter controls transcription of all genes in operon transcribed as 1 unit & a single mRNA is made  promoter = RNA polymerase binding site    operator = DNA binding site of regulator protein AP Biology 2005-2006 Repressor protein model RNA polymerase Operon: operator, promoter & genes they control serve as a model for gene regulation RNA TATA repressor polymerase gene1 gene2 gene3 gene4 DNA promoter operator Repressor protein turns off gene by blocking RNA polymerase binding site. repressor repressor protein 2005-2006 AP Biology Repressible operon: tryptophan Synthesis pathway model RNA polymerase When excess tryptophan is present, binds to tryp repressor protein & triggers repressor to bind to DNA  blocks (represses) transcription gene2 gene3 gene4 DNA RNA TATA repressor polymerase gene1 repressor repressor protein tryptophan promoter operator tryptophan ± repressor protein complex conformational change in 2005-2006 repressor protein! repressor AP Biology Tryptophan operon What happens when tryptophan is present? Don¶t need to make tryptophan-building enzymes Tryptophan AP Biology binds allosterically to regulatory protein 2005-2006 Inducible operon: lactose Digestive pathway model RNA polymerase When lactose is present, binds to lac repressor protein & triggers repressor to release DNA  induces transcription gene2 gene3 gene4 DNA RNA TATA repressor polymerase gene1 repressor repressor protein lactose promoter operator lactose ± repressor protein complex conformational change in 2005-2006 repressor protein! repressor AP Biology Lactose operon What happens when lactose is present? Need to make lactose-digesting enzymes Lactose binds allosterically to regulatory protein AP Biology 2005-2006 Jacob & Monod: lac Operon   1961 | 1965 Francois Jacob & Jacques Monod first to describe operon system  coined the phrase ³operon´ AP Biology Jacques Monod 2005-2006 Francois Jacob Operon summary  Repressible operon  usually functions in anabolic pathways  synthesizing end products  when end product is present in excess, cell allocates resources to other uses usually functions in catabolic pathways,   Inducible operon  digesting nutrients to simpler molecules  produce enzymes only when nutrient is available  AP Biology cell avoids making proteins that have nothing to do, cell allocates resources to other uses 2005-2006 Any Questions?? AP Biology 2005-2006 Fred Sanger 1958 1980 AP Biology 2005-2006 ...
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This note was uploaded on 10/18/2010 for the course BIO 204 taught by Professor O'neal during the Fall '07 term at SUNY Stony Brook.

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