Bacterial Genetics

Question 1

Bacterial genome: haploid or diploid?

Answer 1

haploid. genes exist in single copies.

Question 2

what is a bacteriophage?

Answer 2

a virus that infects bacteria

Question 3

describe the bacterial genome

Answer 3

single, double-stranded, circular DNA molecule

Question 4

what is a transition?

Answer 4

a purine is replaced by a pyramidine or vice versa

Question 5

what is a transversion

Answer 5

a purine is replaced by another purine, or a pyramidine is replaced by another pyramidine

Question 6

what is a revertant?

Answer 6

mutation that restores a wild type phenotype

Question 7

define auxotrophy

Answer 7

the inability to synthesize an essential metabolite such as an amino acid. usually a mutant. the corresponding wild type is called a prototroph (able to synthesize the essential metabolite)

Question 8

a few qualities of bacteria that allow us to select for them?

Answer 8

auxotrophy, ability/inability to utilize a particular carbon source (lactose/glucose), antibiotic resistance

Question 9

2 ways that antibiotic resistance arises?

Answer 9

1. mutation to become resistant

2. transfer of the mutated resistant genes from one bacterium to another

Question 10

is the % of antibiotic-resistant organisms proportional to the length of the abx treatment?

Answer 10

NO, resistant bacteria spontaneously arise all the time (prior to abx exposure), and the abx treatment allows them to become the principal component of a new population.

Question 11

define ‘conditional mutants’. what is an example?

Answer 11

mutations that exhibit a mutant phenotype only under certain conditions. ex: temperature sensitive (ts) mutations: will be normal at permissive temperature, but at a different temp the mutant phenotype is observed. because the mutation allows the protein to assume a normal folding at permissive temp, and at the other temp it folds abnormally.

Question 12

a ts arginine auxotroph: will it grow at 30’ without added arginine?

Answer 12

yes, at 30’ the mutation is silent. at 42’ it is mutated and requires added arginine.

Question 13

how can we study bacteria that are very difficult to isolate?

Answer 13

can analyse SSU rRNA. (small subunit rRNA). highly conserved, but is unique to each species. has universal primers but content is unique (?)

Question 14

describe the structure of a bacteriophage

Answer 14

RNA or DNA genome with protein shell or capsid

Question 15

how do bacteriophages grow?

Answer 15

by infecting an actively growing bacterial culture. the bacteriophage will cause host cell lysis with the repease of progeny phages.

Question 16

how are bacteriophages quantified?

Answer 16

via plaque assay. placed on a plate with bacteria, and the halo of bacterial death is observed. look for morphology of plaque (size, clear v turbid).

Question 17

define lytic and lysogenic

Answer 17

both are categories of the phage life cycle.

lytic: involves phage multiplication and release of newly formed phages, following host cell lysis. virulent phages follow this pathway only
lysogenic: (aka integrative) does not result in production of progeny phage or bacterial killing. the DNA becomes incorporated into the bacterial genome. phage genome then replicates when the bacterial genome replicates.

Question 18

one quality that differentiates virulent from temperate phages

Answer 18

virulent: only uses lytic pathway, produces clear plaques.

temperate phages: produce turbid plaques because can use either lytic or lysogenic pathways.

Question 19

in a bacterium that has undergone lysogeny, what could happen if the bacteria is stressed?

Answer 19

if host bacterium encounters stress, the repressor of the prophage may be de-activated and prophage may excise itself, and undergo a lytic cycle, releasing phages.

Question 20

how do bacteria use restriction enzymes to eliminate consequences of bacteriophage infection?

Answer 20

they use restriction enzymes to cleave the foreign DNA enzymatically at specific DNA sequences.

Question 21

how to bacteria protect their own DNA from restriction enzymes?

Answer 21

they have enzymes that modify their own DNA on the sequences that the enzymes recognize. ie, methylating an amino acid within that sequence.

Question 22

what are transposons?

Answer 22

mobile genetic elements that are integrated into bacterial chromonoes or plasmids, and are capable of jumping from one DNA location to another.

Question 23

what are insertion sequences?

Answer 23

sequences at the ends of transposons that allow them to integrate to various places in the genome.

Question 24

what are the contents of some transposons?

Answer 24

some transposons contain a gene for antibiotic resistance. some duplicate themselves during transposition so they are also retained at their original site.

Question 25

name 3 mechanisms of gene transfer in bacteria

Answer 25

1. transformation
2. transduction
3. conjugation

Question 26

describe transformation

Answer 26

transfer of genetic information to a bacterium following the uptake of naked DNA from outside the cell

Question 27

describe transduction

Answer 27

transfer of a gene from one bacterium to another by a phage that has mistakenly replaced part of all of its genome with some of its host’s DNA

Question 28

describe conjugation

Answer 28

sexual reproduction in bacteria. unequal exchange of genetic information between parents. transfer of genetic information that requires direct cell-cell contact. examples include transfer of conjugal plasmids and transfer of portions of the bacterial chromosome by Hfr (high frequency of transfer) strains.

Question 29

what is the laboratory value of transformation?

Answer 29

recombinant DNA plasmids can be easily introduced into bacteria via transformation.