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Bacteria. Ch 18. Bacteria. Genome – double stranded circular DNA . DNA packed into nucleoid. Reproduction: -Binary Fission - short generation times. http://www.youtube.com/watch?v= gEwzDydciWc. How do bacteria vary genetically?. Mutations Genetic recombination
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Bacteria Ch 18
Bacteria • Genome – double stranded circular DNA
How do bacteria vary genetically? • Mutations • Genetic recombination • Horizontal gene transfer – transfer of genes through means other than sexual reproduction • Types: Transformation, Transduction, Conjugation
Transformation • Free DNA is taken up into cell and expressed • What famous experiment illustrated this?
Transduction • DNA is transferred from one bacterium to another by a virus (bacteriophage). • Bacteriophages accidently pick up DNA from bacteria they infect, and transfer it to other bacteria
Conjugation • Direct transfer of material between bacterial cells through direct cell to cell contact or a bridge-like structure between cells. • Donor cell attaches to recipient cell by using sex pili, which grabs onto recipient cell and then draws in two cells together, forming a bridge between 2 cells
F factor • F factor (fertility factor) is required to produce a pili & donate DNA during conjugation • The F factor in E. coli is made up of 25 genes, which help produce the pili • It can exist as a plasmid or a segment of DNA in the bacterial chromosome • Cells with the F factor are F+, cells without are F-
F plasmid conjugation (from F+ to F-) If only the F factor is transferred, this is NOT recombination – since chromosomal genes have not been transferred.
Conjugation with Hfr bacteria • F factor can also be integrated into bacterial chromosome • Such a bacterial cell is now called Hfr cell (high frequency of recombination) • When chromosomal DNA from Hfr cell enters a F- cell, homologous regions of the Hfr chromosome & F- chromosome can align, so segments of DNA are exchanged. This results in recombination.
A Hfrcell can initiate conjugation with another cell, and tries to transfer entire bacterial chromosome, with F factor last Transfer is not complete, so part of bacterial chromosome is now in new cell New DNA can recombine with host cell DNA