18. Microbial Genetics II

Question 1

generalized transduction:

Answer 1

bacteria chromosome is accidently packaged into a viral capsid
- any gene of the host bacterium can be transferred to recipient and doesn’t require lysogeny

Question 2

specialized transduction:

Answer 2

specific genes near the attachment sites of a lysogenic phage in the host chromosome are transferred
-depends on initial development of lysogeny followed by inaccurate excision

Question 3

abortive transduction:

Answer 3

the transferred DNA is not integrated but often is able to temporarily survive and express

Question 4

CRISPR

Answer 4

clustered regularly interspaced short palindromic repeats- a bacterial immune response to phages, like a DNA antibody

Question 5

describe the two processes of bacterial conjugation

Answer 5

• a pilus forms and perhaps transfers DNA or brings the two cells in close contact with one another to enable transfer
• a chemoattractant gradient brings to the two cells into close proximity

Question 6

incompatibility groups

Answer 6

plasmids are selected based on these groups such that only one version exists in a population
-this is often used for taxonomy purposes

Question 7

the __ is the plasmid origin used in transfer, the __ is the plasmid origin used in normal replication

Answer 7

oriT, oriV

Question 8

how does a plasmid get integrated into the bacterial chromosome?

Answer 8

insertion sequences on the plasmid has counterparts on the bacterial chromosome, leading to homologous recombination

Question 9

Hfr plasmid

Answer 9

a plasmid + bacterial chromosome

Question 10

H’ plasmid

Answer 10

the splicing of the integrated plasmid is sloppy, leading to the formation of a new plasmid

Question 11

how does plasmid integration result in the transfer of a different sequence of bacterial chromosome?

Answer 11

a portion of the plasmid begins as the lead sequence, but bacterial DNA is transferred behind it (instead of the plasma portion)

Question 12

what are the mechanisms of plasmid specified resistance?

Answer 12

• efflux pumps
• degrade enzyme
• modify enzyme
• modification of the antibiotic target
• bypass (specifies a new enzyme that isn’t affected by the antibiotic but does the same thing)

Question 13

what are the mechanisms of chromosomal mediated resistance?

Answer 13

-target alteration through mutation

Question 14

how are transposable elements involved in the transfer of antibiotic resistance?

Answer 14

a transposable element carrying antibiotic resistant elements can pick up and move from the chromosome to a plasmid

Question 15

what is a method that a plasmid can maintain itself in a population?

Answer 15

some plasmids produce a toxin and an anti-toxin-if a bacteria tries to lose a plasmid, the anti-toxin has a shorter half life, allowing the toxin to kill the cell

Question 16

insertion sequences

Answer 16

don’t specify any gene product, just the transposase

-contains inverted repeats at the ends

Question 17

composite transposon

Answer 17

a central sequence bounded by an insertion sequence

Question 18

TnA like elements

Answer 18

not bound to an associated insertion sequence, encodes resistance to penicillin and similar antibiotics (beta lactamase)

Question 19

gene cassettes

Answer 19

a gene and a counterpart att site, confers antibiotic resistance
-free in the environment

Question 20

integron structure

Answer 20

contain an integrase and an att site, as well as a promoter

Question 21

how do chromosomal integrons work?

Answer 21

• during normal conditions, there is neutral drift because mutations don’t affect the cell function
• when a stress occurs, it turns on the integrase leading to a shuffling of the genes and promoters of the cassettes such that you might get something useful to the bacteria

Question 22

transposons must be associated with a:

Answer 22

replicon (a plasmid chromosome phage), they aren’t capable of self-replication within a cell

Question 23

selective/developed resistance

Answer 23

all strains of an organism are initially sensitive to the challenge, over time a percentage of the strains develop resistance

Question 24

what are the two types of resistance and what is the significance?

Answer 24

plasmid and chromosomal

• plasmid resistance can be transferred horizontally (rapid spread)
• chromosomal resistance is slower and only transferred to offspring

Question 25

low copy of plasmids are about ___

high copies are ___

Answer 25

1-6, greater than 10

Question 26

which are conjugative, high copy or low copy plasmids?

Answer 26

high copy

Question 27

low copy plasmids are ___ molecular weights than high copy plasmids

Answer 27

bigger

Question 28

mobilization

Answer 28

the process through which a low copy number can be transferred by a process mediated by a conjugative plasmid

Question 29

intrinsically resistant/ insensitive

Answer 29

already programmed into the basic organism