Bacterial Genetics

Question 1

what was the realization of Griffith’s experiment?

Answer 1

that the polysaccharide capsule was preventing the host’s immune system from killing the bacteria

Question 2

What is meant by high frequency of recomination (Hfr)?

Answer 2

if the F plasmid sequence is integrated into the bacterial chromosome, the cell is designated an Hfr cell

Question 3

which bacteria can make a sex pilus for conjugation?

Answer 3

gram negative. conjugation of gram positive would be uber rare. if you get sharing of DNA with gram positive it probably wasn’t via a sex pilus.

Question 4

if conjugation gets interrupted, which genes are most likely to be shared?

Answer 4

the genes closest to the origin of replication on the plasmid

Question 5

how is conjugation in gram-positive done

Answer 5

they clump together with response to a conjugation related chemical signal- then locally merge cell envelopes, and plasmid DNA is shared using the mechanism as in gram-negative

Question 6

how big is a bacteria phage?

Answer 6

230nm or .23micrometers

Question 7

which phages can switch back and forth from lysogenic to lytic?

Answer 7

temperate phages

Question 8

why would a lysogenic cycle convert to a lytic cycle?

Answer 8

the bacteria could die under exposure to UV radiation, or at high population densities

Question 9

gene for virulence factor is in fact a viral gene, what implication does this have

Answer 9

virulence gene contains much more cytosine and guanine that most genes (which is also likely to be unmethylated – and so, recognized by TLR 9)

Question 10

what are some examples of lysogenic conversion with virulence factors

Answer 10

diphtheria toxin, cholera toxin

Question 11

during which phase of the growth curve is cholera toxin expressed at the highest levels?

Answer 11

end of log phase

Question 12

what does diphtheria toxin do to eukaryotic cells

Answer 12

destroys their ability to translate proteins

Question 13

what is an example of homologous recombination

Answer 13

uptake of an alt gene for the transpeptidase enzyme by a beta-lactam sensitive strain of bactera from a bacteria of the same species that was bata-lactam resistant

Question 14

give an example of nonhomologous recombination

Answer 14

occurs b/w dissimilar DNA sequences and generally produces insertions or deletions or both. Neisseria gonorrheae isolates have been identified that have DNA sequences from human cells in their chromosomes

Question 15

what makes a bacteria competent?

Answer 15

they express DNA uptake molecules on their cell surfaces. Nucleases on the DNA uptake protein cut and degrade one strand of the DNA, and import the other strand into the cell.

Question 16

where does the new DNA come from in Natural Transformation?

Answer 16

the environment- you need to have competent bacteria and recombinase which is made by recA gene

Question 17

What are viruses called that only kill the bacteria they infect?

Answer 17

virulent phages. This is a lytic cycle.

Question 18

how does the virus get out of the cell in a lytic cycle?

Answer 18

it makes proteins that lyse the bacteria from the inside via proteins

Question 19

not close relatives: Did this happen all on its own/is the transferred DNA in the recipient’s chromosome?

Answer 19

yes, natural transformation

Question 20

not close relatives: Does it involve a designed plasmid being shocked into the recipient?

Answer 20

yes, artificial transformation

Question 21

what would stop both forms of transformation?

Answer 21

DNase added

Question 22

close relatives: happened with gram-postive bacteria OR transferred DNA is in the recipient/s chromosome: There’s a mention of a lytic phage OR a bunch of random genes are transferred every time

Answer 22

Generalized transduction

Question 23

close relatives: happened with gram-postive bacteria OR transferred DNA is in the recipient/s chromosome: No phage is necessarily mentioned OR there’s co-transfer of a virulence gene like an A/B toxin plus some other gene

Answer 23

specialized transduction.

Question 24

Close relatives: A plasmid was transferred/ you can stop the DNA transfer via shaking

Answer 24

conjugation

Question 25

what is the key mechanism bacteria use to control gene expression

Answer 25

production of different sigma factors under different environmental conditions

Question 26

what property of pathogenicity in genes could a researcher uses to find their location in a genome?

Answer 26

these genes typically have lots of CGs and very little AT, so you could look for a region with lots of CGs

Question 27

in general what are anabolic (energy using) pathways down-regulated by?

Answer 27

their end products

Question 28

in general, what are catabolic (energy generating) pathways up regulated by?

Answer 28

their substrates

Question 29

the anabolic trp operon codes for enzymes that make tryptophan, if present what would repress transcription of the trp operon?

Answer 29

since all of the genes to make tyrptophan are found on the same operon, if tryptophan is present it will bind to the promoter region and prevent transcription

Question 30

the catabolic lac operon gene products break down lactose in order to acquire glucose to make ATP. this operon is normally represses how would you relieve repression of the lac operon

Answer 30

if lactose was available, you would bring it into the cell. lactose will pull off the repressor to allow RNA polyerase to transcribe DNA into RNA

Question 31

explain the transposition mutation

Answer 31

inverted repeats make it more likely that the gen gets moved from one location to another during normal replication. It will now be regulated with the new location and will be subject to that operons control

Question 32

how does rifampin work?

Answer 32

Disables RNA polymerase –> stops transcription and kills bacteria. Binds in the site on the RNA polymerase where the sigma subunit would have normally bound to inititate transcription of DNA into RNA

Question 33

How do macrolides work?

Answer 33

They are -“mycin”s that prevent the large subunit from continuing translation (macroSLIDES)

Question 34

Even though it can vary greatly what is the consensus shine-dalgrano sequence?

Answer 34

AGGAGG

Question 35

Siderophore

Answer 35

molecule secreted by bacteria to collect iron from the environment, transport iron back into the bacterial cell.

Question 36

What is the order to Rx 1st gen beta-lactams?

Answer 36

Penicillin, amoxicillin, ampicillin