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Since asexual reproduction is used, how does Bacteria transfer DNA?

Since asexual reproduction is used, how does Bacteria transfer DNA?. Transformation gene alteration by the uptake of naked, foreign DNA (plasmid) from the environment Transduction phages that carry bacterial genes from 1 host cell to another

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Since asexual reproduction is used, how does Bacteria transfer DNA?

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  1. Since asexual reproduction is used, how does Bacteria transfer DNA? • Transformation • gene alteration by the uptake of naked, foreign DNA (plasmid) from the environment • Transduction • phages that carry bacterial genes from 1 host cell to another • generalized~ random transfer from host #1 to host #2 • specialized~ specific incorporation of prophage DNA into host chromosome • Conjugation • direct transfer of genetic material btwn two bacterial cells; forms cytoplasmic bridges; sex pili used

  2. Searching for Genetic Material http://www.dnalc.org/view/16375-Animation-17-A-gene-is-made-of-DNA-.html

  3. Generalized Transduction Animations • http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html Specialized Transduction Animations • http://highered.mcgraw-hill.com/sites/0072552980/student_view0/chapter9/animation_quiz_4.html

  4. Conjugation • Conjugation • the direct transfer of genetic material between bacterial cells that are temporarily joined • The transfer is one-way: One cell (“male”) donates DNA, and its “mate” (“female”) receives the genes • Sex pili are used in the transfer of DNA

  5. LE 18-17 Sex pilus 5 µm

  6. Bacterial Factors/Plasmids • F (fertility) factor: codes for the ability to produce sex pili (bacteria are either F+ or F-). Can exist within chromosome or as a plasmid. • R (resistance) Plasmid: codes for antibiotic drug resistance

  7. The F plasmid and Conjugation • Cells containing F factor in the form of an F plasmid (F+ cells) function as DNA donors during conjugation • F+ cells transfer DNA to an F recipient cell

  8. Conjunction and transfer of an F plasmid From and F+ donor to an F– recipient F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome

  9. The F factor (integrated into chromosome) and Conjugation • Chromosomal genes can be transferred during conjugation when the donor cell’s F factor is integrated into the chromosome • A cell with a F factor integrated into the circular DNA chromosome is called an Hfr cell • The F factor of an Hfr cell brings some chromosomal DNA along when transferred to another F– cell

  10. F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell Conjunction and transfer of an F plasmid From Hfr cell to an F– recipient  results in recombination F+ cell Bacterial chromosome Conjunction and transfer of an F plasmid from and F+ donor to an F– recipient Hfr cell F+ cell F factor Hfr cell F– cell (b)

  11. HFR Animations • http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_4.html

  12. R plasmids and Antibiotic Resistance • R plasmids resist various antibiotics • When a bacterial population is exposed to an antibiotic, individuals with the R plasmid will survive and increase in the overall population

  13. Transposable Elements • Segments of DNA that can move around in a cell’s genome, thus increasing genetic recombination • Can move around in same chromosome, from plasmid to chromosome (or vice versa), or from plasmid to plasmid • The simplest transposable elements (“jumping genes”), called insertion sequences, exist only in bacteria • An insertion sequence CONTAINS DNA for a single gene for transposase • an enzyme catalyzing (allows) movement of the insertion sequence from one site to another within the bacteria genome

  14. Transposable Elements Animation • http://highered.mcgraw-hill.com/olc/dl/120082/bio36.swf

  15. Insertion sequence A T C C G G T… A C C G G A T… 3 5 3 5 T A G G C C A … T G G C C T A … Inverted repeat Transposase gene Inverted repeat The inverted repeats are backward, upside-down versions of each other and only a portion is shown. The inverted repeat sequence varies from one type of insertion sequence to another. Figure 18.19a

  16. Transposons • Transposable elements called transposons are longer and more complex than insertion sequences • In addition to DNA required for transposition (i.e.-transponase), transposons have extra genes that “go along for the ride,” such as genes for antibiotic resistance

  17. Transposon Animations • http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_5.html

  18. REVIEW • How do bacteria exchange DNA or acquire NEW genes? • Transformation • Trandsduction (both generalized and specialized) • Conjugation • Insertion sequences and Transposons

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