Chapter 5 - Chapter 5 The Genetics of Bacteria and Their...

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Chapter 5: The Genetics of Bacteria and Their Viruses I) Bacteria are prokaryotes (DNA not enclosed in a membrane-bound nucleus) A) Typically single molecule of double-stranded DNA enclosed in a circle B) Often have extra DNA elements in plasmas C) Reproduce asexually by cell growth and division 1) Do not undergo meiosis 2) 1 2 4 8 16 … cells (until nutrients are exhausted or toxic waste builds up on plates) 3) Rarely are two complete chromosomes brought together in reproduction— usually union of one complete chromosome and fragment of another D) Nutritional mutants 1) Prototrophic—wild type, can grow and divide on minimal media 2) Auxotrobic—cells wont grow unless medium contains one or more specific cellular building blocks E) Resistant mutants—divide and form colonies in the presence of an inhibitor II) Bacteriophages (phages)—viruses that infect bacteria A) Genetic material can be DNA or RNA B) Nonliving—cannot reproduce alone—must parasitize living cells and use their molecular machinery C) Consists of a nucleic acid “chromosome” surrounded by a coat of protein molecules D) During infection, attaches and injects genetic material into bacterial cytoplasm 1) Takes over cell machinerary, turns off synthesis of bacterial components and begins making phage components 2) Lysis occurs and lysate (population of phage progeny) is released E) Mapping phage chromosomes 1) Create a mixed infection (aka double infection) 2) RF= (# of recombinants)/total plaque 3) Complications: a) Further recombination can occur in same cell after initial b) Can take place b/t genetically similar phages as well as b/t different types 4) Selective system—only desired rare event can produce a certain visible outcome F) Two types: 1) Virulent phages—immediately lyse and kill host 2)
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