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Unformatted text preview: Lecture 02 - Bacterial Genetics and Physiology M I-14d. Describe the structure of the bacterial chromosome Complete genome sequences have been obtained for essentially all organisms of medical significance- Bacterial chromosomes are circular or linear DNA molecules about 2-5 x 10 6 bp (encoding 2-5 thousand genes) o one chromosome per bacteria (except a few ie. those bacteria causing cholera)- There is relatively little non-coding DNA and introns are generally absent o Bacteria are very efficient in terms of their genome they are relatively little DNA that doesnt code for genes (unlike us) o Most DNA functional (since its a small chromosome anyways) Bacterial chromosome/DNA o Packaged into organized structure inside the bacteria cell Lots to cram (DNA) into a very small space When bacteria are lysed the bacteria cell the DNA comes spilling out the size of the DNA relative to the size of the bacteria (DNA lots : Bacteria Little) All the DNA must be packaged and replicated o Bacteria replicate in 20 mins (so this entire chromosome have to replicated in 20 mins and separated into daughter cells) Have to keep them from tangling up (there are enzymes to do this -- some used in antibiotics targets) The Genes- Genes are frequently clustered according to biochemical function and transcribed as a unit forming an operon o the genes can be co-regulated if theres similar functions- Genes for essential structures and metabolic functions are arranged in a relatively constant order characteristic of a species o i.e. the house keeping genes is kept constant in the bacteria BUT the order varies , sequence of the gene may differ among the species - Many bacteria have a large number of phage and phage remnants in their genomes, and these differ in individual strains of a species o it allows for strain typing procedures (show that bacteria strain are related to one another b/c the size of certain segment of the genome have phages that are inserted/deleted)- Strains of a species may also differ by many insertions and deletions of large and small DNA segments o Strains of different species o i.e. e. coli from us vs the professor the genome (basic structure is similar house keep gene similar) But there are a lot insertions and deletions, pieces of phages here and there restriction enzyme analysis and other techniques (strain typing) you can tell the different in the strain typing (you can trace the transmission of the strains) very useful tool in EPI to trace bacteria M I-14g. Describe the structure of plasmids their role of in antimicrobial resistance and pathogenesis Plasmids: (another form of DNA)- Most bacteria have accessory genetic elements consisting of circular or occasionally linear DNA molecules called plasmids (smaller in size than chromosome) - The number and type of plasmids can differ between individual strains of a species , contributing to genetic diversity- i.e. E. coli it can have several i....
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- Spring '11