Bacterial Genetics

Question 1

3 ways of passing genetic information between bacterium

Answer 1

1. Conjugation
2. Transformation
3. Transduction

Question 2

Conjugation (general)

Answer 2

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

Question 3

Transformation (general)

Answer 3

involves the transfer of genetic information by naked extracellular DNA

Question 4

Transduction (general)

Answer 4

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

Question 5

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

Answer 5

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

Question 6

Minimal media

Answer 6

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

Question 7

Prototrophs

Answer 7

any strain of microorganism that can grow in solely minimal media

Question 8

Auxotrophs

Answer 8

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

Question 9

Lederberg and Tatem experiment

Answer 9

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)

Question 10

What direction does conjugation occur in?

Answer 10

unidirectional transfer of genetic material

from F+ (or HFr) to F-

Question 11

Davis U-Experiment 1

Answer 11

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

Question 12

F-pilus

Answer 12

hairlike tubular structure that allows for bacterial conjugation between 2 cells

Question 13

Basic steps of conjugation

Answer 13

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)

Question 14

Wollman and Jacob

Answer 14

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

Question 15

Difference between F+ cell and Hfr cell

Answer 15

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

Question 16

Why does Hfr not pass its F-factor?

Answer 16

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

Question 17

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

Answer 17

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

Question 18

Competent bacteria cells

Answer 18

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

Question 19

Steps of transformation

Answer 19

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

Question 20

Bacteriophages

Answer 20

viruses that use bacteria as their hosts

Question 21

How do viruses bind to bacteria?

Answer 21

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

Question 22

2 cycles that viruses can trigger

Answer 22

1. Lytic: kills the host

2. Lysogenic: postpones killing the host

Question 23

Lytic cycle

Answer 23

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

Question 24

Lysogenic cycle

Answer 24

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

Question 25

When does transduction occur?

Answer 25

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

Question 26

Zinder and Lederberg Experiment

Answer 26

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