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24 Cards in this Set

  • Front
  • Back
Horizontal Gene Transfer in Bacteria
* how DNA (genes) move around in the bacterial world

1) transformation
2) conjugation
3) transduction
4) transposition
Bacterial Chromosome
* genome: circular, unique origin of replication, supercoiled

* haploid, but multiple copies in growing bacteria
Conversion Factors
* average bacterial genome = 3,000 kb

* average bacterial gene = 1 kb

* average bacterial gene encodes an average protein of 36 kDa

* average bacterium encodes 3,000 genes arranged in 1,000 operons
1) synthesize oligonucleotides from each gene

2) spot the oligonucleotides onto a microscope slide

3) isolate RNA from the bacteria and label with red dye

4) grow bacteria under conditions A and B

5) probe the chip with labeled RNA

6) red = RNA produced
green = not produced

7) place in scanner to quantitate intensity of dyes
Properties of Plasmids
* sex/fertility: encode capacity for transfer via conjugation

* drugs: R-factors encode antibiotic resistance (multiple drug resistances on single plasmid)

* rock and roll: heavy metal resistance

* virulence genes

* bacteriocins: molecules made by one bacterium to kill others

* iron acquisition: help bacteria compete with host for iron

* replication functions
Main Function of Plasmids
the function of plasmids is to provide a SELECTIVE advantage upon the host bacterium under certain environmental conditions

* if you remove the selective condition you might remove the plasmid
- only a small % of bacteria need to harbor the plasmid
* loss of a plasmid

* plasmids are lost based on how faithfully they partition between daughter cells
Host Range of Plasmids
* can be narrow or broad

* some plasmid rep'n functions only exist in certain species
Promiscuous Plasmids
* plasmids with broad host ranges

* can be transferred and maintained

Ex. there are plasmids that can replicate in most Gram negatives
Copy Number
* number of plasmids per chromosome equivalent

* ranges from 1 to high copy (30 per chrm equiv)

* genetically controlled: can get high copy number via mutation in copy number control
Incompatibility Groups of Plasmids
* 26 incompatibility groups

* plasmids from the same group have the same rep'n fxn so cannot exist together
Shuttle Plasmids
* have an origin of rep'n from a Gram neg and a Gram pos

* can grow in E. coli and in second host species

* often incorporates Tra fxns from wide host range plasmids to move between species of bacteria through conjugation
Tra (transfer) functions
* transfer regions wide host range plasmids can transfer

* can put Tra region into the chrm so that when plasmid gets placed in bacterium, it becomes mobilized
* mediated by the Tra proteins, which encode the pili

* Pili are grappling hooks that mediate bacterium-bacterium interxns

* allows plasmids to be transferred via mobilization

* regulated process because pili often act as phage receptors

* recA-independent process
* process by which plasmids are transferred to other bacteria

* gene on plasmids sneaks over to a conjugated bacterium via another gene called mob
recA-dependent process
1) a single linear piece of DNA goes into the cell

2) DNA finds its homolog

3) double crossover

4) replacement of genes already there

* bacteria only exchange DNA rec-dependently with other members of the same species
* recombination gene

* necessary for the genetic exchange between homologous DNA from two different bacteria
Natural Transformation (Competence)
* process in which bacteria naturally take up naked chromosomal DNA

* rec-A dependent: genetic exchange between homologous DNA from two bacterium

* reqs competent bacteria

* 15 kb incorporated (15 genes)
Unnatural Transformation
* process of introducing plasmids into bacteria via calcium and heat shock

* recA-independent
* process of introducing plasmids into bacteria by inducing holes in the cell membrane via electronic pulses

* rec-A independent
Lysogenic Pathway
1) virus particle attaches to host cell

2) it injects its DNA into host cell

3) viral DNA is integrated into host DNA (prophage)

4) cell undergoes normal cell growth and more copies of the prophage are made
Lytic Pathway
1) virus particle attaches to host cell

2) it injects its DNA into host cell

3) viral DNA is integrated into host DNA (prophage)

4) viral DNA is replicated

5) coat proteins are synthesized

6) viral DNA is packaged into coat proteins

7) lysis of host cell
Generalized Transcduction
* technique for mapping genes and strain construction

* selecting a transduction event (gene) in a virus packaged with chromosomal DNA via a selective marker

* recA-dependent
Specialized Transduction(Phage Conversion)
Option 1:
- phage is encoded in the genome
- uses this to move from one bacterium to another

Option 2:
- package one piece of chromosomal DNA adjacent to the phage DNA

* phage conversion: phage convert non-pathogenic bacteria into pathogenic bacteria by lysogeny

- many phage encode determinants of pathogenesis

* recA-dependent