Micro 4

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Horizontal exchange in bacteria is

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Not an obligatory process
Important for evolution/drug resistance/
pathogenesis

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there are 3 horizontal gene exchange mechanisms

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Transduction
Conjugation
Transformation

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Transduction

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Virus as vectors

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Conjugation

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most genetic transfers in nature)
Plasmid-mediated, also transposon

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Transformation

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Naked DNA

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Horizontal gene transfer, also known as lateral gene transfer, is any process in which

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an organism transfers genetic material to another cell that is not its offspring.

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Vertical gene transfer occurs when an organism

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receives genetic material from its ancestor.

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Bacteria that have received DNA from another bacterium by transduction are called

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transductants

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hage dna is incorporated into host DNA by

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recombination

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Transduction occurs very rarely, but transductants can be selected using

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markers such as antibiotic resistance genes.

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specialized phage transduction occurs when

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chrosomosal regions located next to phage insertion site get packaged and delivered into new bacterial host

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Specialized vs generalized phage transduction

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Generalized - transfer of ANY bacterial gene or chromosomal region
Specialized - transfer only of regions adjacent to phage insertion site.

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Plasmid conjugation

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Plasmid encodes machinery to make pilus and it bonds to receptor in neighboring bacterial cell and then it retracts to bring the bacteria closer to each other. There's a nick generation origin of transfer, and single stranded DNA is transferred

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Plasmid conjugation has a special nick called

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oriT

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Plasmid sometimes are referred as F+ or F-. The F+ transfers factor F and other components to a F- cell, the the cell becomes

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F+ and can now transfer the same elements to another F-

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Recombination between F factor and chromosome occurs at

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specific site on each. Insertion of F factor into chrosome results

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When an F factor becomes integrated into the chromosome of an F+, it makes a

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the cell a high frequency of recombination (Hfr)

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The amount of Info transfer by conjugation depends on

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Depedent on how long the Pillus last determines the amount of DNA is transferred. Sometimes the plasmid DNA is not even transfer

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Conjugation important characteristics

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The donor DNA is enclosed within a pilus; not subject to degradation from external DNases
Donor cell keeps a copy of the plasmid DNA, only one strand of the donated portion is transferred to the recipient cell
Conjugation bridge is relatively unstable
Conjugation is not limited to the member of the same species, so plasmids carrying antibiotic resistance can spread to different bacterial populations

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Naturally transformable bacteria will take up DNA from their environment without special treatment. The state in which they can do this is called

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natural competence. Bacillus subtilis, Neisseria gonorrhoeae, streptococcus pnemoniae

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Artificially induced competence

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Treatment of cells with calcium and magnesium salts
*Electroporation - distorts membrane and enables large molecule uptake

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Homologous recombination

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arises when closely related DNA sequences from two distinct genetic elements are combined in a single element.

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Site-specific recombination

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ccurs at a specific sequence which is present in both non- homologous DNA molecules.

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Transpositional recombination

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a mobile genetic element is inserted into a target DNA.

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Rec A homologus recombination mechanism

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Rec a needs a single strand DNA that shows homology when you have a nick in DNA and if they strands come apart the single strand is recognized by rec a and binds to a single strand and matches to another DNA molecule that has homology. Then you generation the holiday junction, if y move along you get fragments you end up recombined molecules. You get some strand exchange. It breaks apart. You have to have ligation of open ends change of strands between 2 differents molecules. The process is most Efficient when there's more similarity if the DNA is different then it falls off

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Rec A mechanisms need special proteins for binding of DNA known as

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SSB protens which bind to dna RIGHT after the nick is made

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Homologuys dna recombination can happen in 2 ways

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Double crossover and single crossover "campbell" like
look it up

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Phage DNA site specific recombination characteristics

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Recombination enzymes specific for that sequence "Integrase"
-Not RecA dependent *Small sequences sufficient
(as small as 3-5 bp)

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Homologous recombination characteristics

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-Any sequence of 50bp or greater for homology
-Rec A mediated
-Works best with large similar regions of DNA

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Whats the Bacterial DNA repair known as SOS response?

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DNA damage induces the expression of >30 genes in bacteria whose products contribute to DNA repair and recombination.
-Damage may be caused by UV irradiation, formation of thymine dimers, double strand breaks, or anything that halts DNA replication.

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Induction of sos

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DNA damage causes single stranded breaks, and reca bonds to it. Lexa is a represor and sits in the promoter region. Rec a + sdna activates Lexa so it moves from represor and downstream gene for repair are made. Error prone repair(UmuD) adds nucleotides doesn't matter which ones but it does so when truncated trasncrpipts occur.

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Excision repair

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DNA with dimer
Dimer recognized & cut
Dimer excised
GAP filled by DNA polymerase Nick sealed by DNA ligase

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Recombination based repair

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Rec A/Rad51 mediated
If there a dsbreak, reca recognizes the sdna, and if there's another copy of that sequence, reca takes the sdna here and uses recombination to integrarpte and restore the sequence. Lipase comes and fills in the gaps

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Non homologus end joining repair

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Ku and LigD or Lig4 mediated happens only in non replicatin cells (quiescent)

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Usually antibiotics target

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target many of the components involved in transcription and translation

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Bacterial Operon Definition:

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A group of genes that functions as a single transcription unit. It is comprised of an operator, a promoter, and one or more genes that are transcribed as a single polycistronic mRNA.

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the lac operon

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Lac represor sits on the Operon and prevents synthesis of all the downstream genes..lactose binds to the repressor and genes are synthesized