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Chapter 5-2.docx

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University of Lethbridge
BIOL 2000
Joseph Rasmussen

Chapter 5-2 Properties of the F-Factor (Plasmid)  Enables the production of pilli o Proteniaceous attachment tube between cells  Able to replicate during cell division and during conjugation o Will transfer the F plasmid to their offspring o F+ remains constant in the population o Each daughter cell will gain this F+ plasmid  Prevents conjugation between two F+ cells o One must be F- for conjugation to occur F Plasmids transfer during conjugation  Transfer of single-stranded DNA o F+ is donor o F- is recipient o Only one direction of transfer  F+ will create the pillis  Replication in both donor and recipient  Rolling circle replication in donor o F plasmid DNA is double stranded and circular o The defined position at the origin will be cut o Serves as a starting point for the transfer process o Origin point is the first point to arrive in the F- cell o The arrow head will indicate the direction of DNA transfer  The donor cell does not loose DNA o DNA synthesis is replacing the DNA that is being transferred o The recipient is also synthesizing the template, to create a double stranded DNA molecule  DNA synthesis in both cells are ensuring both cells have F+ plasmid double stranded DNA  F Plasmid DNA will only be transferred o No other DNA will be transferred Clicker question  During Bacterial conjugation, which one of the following events would not be expected to occur? o An F- cell would be converted to a F+ cell o An F+ cell would generate pili to attach to F- cells o DNA would be replicated in the F+ cell o DNA would be replicated in the F- cell o All of the above would occur Lederberg and Tatum  Prototroph can be detected at a low frequency o 1 in 10 million cells  Two strains, both auxotrophic o Strain A= bio- met- o Strain B= thr- leu- thi-  Transferred alleles (chromosomal) are not part of the F plasmid Cavalli- Sforza  Created sub cultures from F plasmid, then conjugated them  Observations o Occasionally F+ strain become strains with a High frequency of recombination  Hfr strains  1000x more frequent transfer chromosomal genes than regular F+ strains o Hfr X F-  Only rarely F= converted to Hfr or F+  When the Hfr cells undergo conjugation they are not transferring much to the F- cells Integration of the F plasmid creates an Hfr strain  Occurs when start with F+ cell that has a free F+ plasmid  Hfr is formed when that F+ plasmid integrates itself into the bacterial chromosome  When the Hfr strain undergoes conjugation event, it will be transferred  F plasmid has sequence that is homologous to the chromosome of the bacterial chromosome  Homologous pairs come together due to their similarities o Crossing over can occur o The F Plasmid can be integrated through crossing over  Integration event  The two sequences are flanking the F plasmid portion  The DNA can loop back on itself at the two IS sections, which can make it back to its ori
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