BACTERIA Single celled organismsin have no nucleus have

BACTERIA ۞Single celled organismsin ۞have no nucleus ۞have a single chromosome ۞have a short generation time ۞convenient to study genetically

Luria and Delbrück (1943) ü Luria and Delbrück demonstrated that bacteria can undergo a change in which they become resistant to infection by a particular phage. ü this change arises spontaneously, rather than as a response (adaptation) to the phage.

Luria and Delbrück (1943) ü bacteria can in herit traits (e. g. , sensitivity or resistance to a phage ), and occasionally this inheritance can undergo a spontaneous change (mutation) to an alternative inheritable state. ü bacteria exhibit genetically determined characteristics. But because of their simplicity, bacteria would be ideal experimental systems in which to elucidate the nature of the genetic material and the traitdetermining factors (genes) of Gregor Mendel.

Bacterial growth curve Figure A-5 (p. p. 803)

�Bacteria Exchange DNA by Sexual Conjugation, Phage-Mediated Transduction, and DNA-Mediated Transformation. F(fertility) plasmid: 游離質體，接合作用時複製、 傳遞的物質。 F-: 本身沒有F plasmid(游離質體) F+: 本身帶有F plasmid(游離質體)，可以傳遞細菌 給別人 F，: 一段實體除了含F plasmid，還多了一段不小 心複製的chromosome DNA片段。 F factor: 某一細菌其F plasmid重組進去自己本身 的chromosome， 此F plasmid為F factor。 Figure A-6 (p. p. 804) Hfr(High frequency of recombination): 含有F factor的染色體，具有高度自發性重組，容易產 生自發性突變。

The three forms of F plasmid-carrying cells �F+ cells harbor a single copy of the F- plasmid which replicates as an independent mini chromosome. �In an Hfr strain, the F-plasmid is integrated into the bacterial chromosome and is replicated as part of that larger molecule. � In an F’-strain, an F-plasmid that had previously been integrated into the host chromosome excises, bringing with it a region of adjacent host DNA.

The three forms of F plasmid-carrying cells �If the donor cell is an F+ strain, it copies and transfers just the F-plasmid; if an F’, it copies and transfers the Fplasmid along with the incorporated host DNA; if an Hfr, it copies and transfers varying amounts and parts of the host chromosome, depending on the site of integration and the duration of mating. Once in the recipient, chromosomal DNA from the host is available for recombination, and hence genetic exchange, with the genome of the recipient cell.

phage-mediated generalized transduction

Transposon-generated insertional mutagenesis

Transposon-generated lac. Z fusions

Bacteria 1. Studies on the Molecular Biology of Bacteria Have Been Enhanced by Recombinant DNA Technology, Whole. Genome Sequencing, and Transcriptional Profiling 2. Biochemical Analysis Is Especially Powerful in Simple Cells with Well-Developed Tools of Traditional and Molecular Genetics 3. Bacteria Are Accessible to Cytological Analysis 4. Phage and Bacteria Told Us Most of the Fundamental Things about the Gene 5. Synthetic Circuits and Regulatory Noise

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