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Flashcards in Bacterial Genetics Deck (26)
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1
Q

3 ways of passing genetic information between bacterium

A
  1. Conjugation
  2. Transformation
  3. Transduction
2
Q

Conjugation (general)

A

involves the transfer of DNA from a donor cell to a recipient cell through a sex pilus

3
Q

Transformation (general)

A

involves the transfer of genetic information by naked extracellular DNA

4
Q

Transduction (general)

A

involves the transfer of genetic information to a bacterium from a bacteriophage or between bacterial or yeast cells mediated by a phage vector

5
Q

Why do we use an agar plate vs. a liquid growth medium?

A

agar plate allows us to tell the cells apart and quantify/isolate colonies

6
Q

Minimal media

A

synthetic culture that contains only the material essential for the growth of a WT organism

7
Q

Prototrophs

A

any strain of microorganism that can grow in solely minimal media

8
Q

Auxotrophs

A

any strain of microorganism that differ from the WT strains and cannot grow on minimal media

9
Q

Lederberg and Tatem experiment

A

two strains of bacteria that were each unable to synthesize DIFFERENT proteins were combined

together, the two auxotrophs were able to produce prototrophs

shows that genetic exchange occurred between the two strains (highly unlikely that this occurs by chance alone)

10
Q

What direction does conjugation occur in?

A

unidirectional transfer of genetic material

from F+ (or HFr) to F-

11
Q

Davis U-Experiment 1

A

Medium can pass back and forth between cells, but the cells cannot

No prototrophs were generated

Shows that direct contact is needed for conjugation to occur

12
Q

F-pilus

A

hairlike tubular structure that allows for bacterial conjugation between 2 cells

13
Q

Basic steps of conjugation

A
  1. F+ has a F-factor plasmid that encodes for the formation of the F-pilus
  2. Endonuclease enzyme separates the 2 strands of the F-factor plasmid
  3. One strand moves across the plasmid
  4. Separated plasmid strands are replicated in each cell
  5. Ligase closes the two circles

(now both cells have the ability to code for the F-pilus)

14
Q

Wollman and Jacob

A

mixed HFr and F- strains and used interrupted mating technique to map genes by time

shows that genes were transferred at different points of entry and in different directions

proposed that DNA is circular

15
Q

Difference between F+ cell and Hfr cell

A

F+ cell has an F-factor plasmid that can be passed

Hfr cell has F-factor plasmid integrated into the main chromosome as the point of origin

16
Q

Why does Hfr not pass its F-factor?

A

Because it is embedded as the point of origin and would be the last thing to be passed between a cell

17
Q

Why does (F+) + (F-) result in any recombination?

A

at low rates, F-factor plasmid will randomly integrate itself into the main chromosome

this results in some recombination taking place

creates rare, newly formed Hfr cells

18
Q

Competent bacteria cells

A

the small number of bacteria cells that are able to express the correct protein receptor to take up extracellular “naked” DNA from the environment

19
Q

Steps of transformation

A
  1. Competent bacteria cell takes up the extracellular DNA
  2. DNA strands separate
  3. Nucleases digest one of DNA strands
  4. Other strand pairs with host cell DNA and forms a heteroduplex
  5. after one round of cell division, a transformed and an untransformed cell are produced
20
Q

Bacteriophages

A

viruses that use bacteria as their hosts

21
Q

How do viruses bind to bacteria?

A

they have tail fibers that recognize specific receptors and bind to bacteria

22
Q

2 cycles that viruses can trigger

A
  1. Lytic: kills the host

2. Lysogenic: postpones killing the host

23
Q

Lytic cycle

A

Proteins are produced that shut down the host’s transcription and stimulate replication of the viral genome

Lysozyme enzyme is produced by a viral gene that breaks linkages between structural sugars in the bacterial cell wall

Cell wall breaks and new phages can infect neighboring bacteria cells

24
Q

Lysogenic cycle

A

Prophage is inserted into the hosts main chromosome

Prophage is replicating with the normal bacterial chromosome

When the prophage is activated, the lytic cycle is activated which results in the host’s death

25
Q

When does transduction occur?

A

occurs when the virus accidentally transfers some of another bacteria’s DNA when it infects a new cell

this does not happen on purpose

it is because of random cutting during replication

26
Q

Zinder and Lederberg Experiment

A

used U-tube and observed prototrophs on one side

knew it was not transformation because they added DNAase to break down extracellular DNA

used a new filter with smaller pores that would block a virus from moving across the filter. they observed no prototrophs

indicates that transduction is occurring