Lec8 Bacterial Genetics

Question 1

What are the genetic characteristics of prokaryotes?

Answer 1

• haploid genome
• genes arranged in operons
• no splicing of mRNA
• mutations/selections make population change rapidly

Question 2

What are plasmids?

Answer 2

• self-replicating DNA units with accessory genes
• contain many genes required for virulence
• can also contain genes for resistance

Question 3

What are 4 mech of mutation

Answer 3

• replacement
• deletion
• insertion
• inversion

Question 4

What are mutation replacements? how frequent?

Answer 4

• spontaneous freq. 10^-6

- operon struct so stop/start mut have polar effects

Question 5

What type of mutation is the one in RNA-pol that gives rifampin resistance?

Answer 5

point mutation

Question 6

what type of mut causes beta-lactmase change in substrate specificity?

Answer 6

point mutation

Question 7

What time of mutation causes flagellar synthesis to evade immune response?

Answer 7

framseshift as microdeletions

Question 8

what are 3 types of genetic exchange?

Answer 8

• transformation
• conjugation
• transduction

Question 9

What is transformation?

Answer 9

• gene transfer from donor
• efficiency affected by DNA size and state
• it is sensitive to nuclease [DNAse]
• works for bacillus, haemophilus, neisseria, streptococcus recipients
• double strand DNA received by donor, one strand enters cell and other degraded, get recombination by double crossing over into recepient plasmid
• after recplication get 1 transformant and 1 nontransformant

Question 10

what is conjugation?

Answer 10

• dna transferred from bacteria donor F+ cell to recipient F- cell by direct contact
• transfer mediated by pilus [tube-like struct] between cells through which plasma DNA passes
• DNA transfer unidirectional
• both donor and recipient end up with a full copy of the plasmid
• conjugation also involves transfer of plasmids that carry antibiotic resistance
• works in e coli, gram negatives

Question 11

what is transduction?

Answer 11

does not require physical contact of cells
DNAse resistant
happens via lytic or lysogenic cycle

DNA transferred from one bacterium to another by a bacteriophage [virus]

Question 12

What are bacteriophages?

Answer 12

viruses that infect and replicate within bacteria

Question 13

What is the lytic cycle

Answer 13

• virus enters plasma membrane and releases genetic material into cell
• make huge amounts of virus
• kill cell during replication

Question 14

what is the lysogenic cycle?

Answer 14

• no progeny particles produced
• infected bacterium survives
• phage DNA integrates into bacterial chromosomes
• phage DNA transmitted to each bacterial progeny when cell divides
• virus integrates and is latent

Question 15

What do you call phage that is capable of lysogenic cycle?

Answer 15

temperate

Question 16

Which phage species can undergo lytic cycle? what do you call phages capable of lytic cycle but not lysogenic?

Answer 16

all phages can undergo lytic

if can only do lytic –> virulen

Question 17

mech of lytic infection causing transduction

Answer 17

in lytic infection: transducing phage accidentally pakacages piece of bacterial chromosome into a virus particle instead of its own viral dna, carries the bacterial DNA then delivers it to recipient when it is trying to infect in, injected bacterial DNA inserted into recipient chromosome by homologous recombination

Question 18

How much bacterial DNA does a typical P1 bacteriophage contain?

Answer 18

50 genes [80 kb bacterial DNA]

Question 19

What is relationship of relative location of two genes and probability of simultaneous conduction?

Answer 19

• if two genes closer together, greater frequency of cotransduction

Question 20

What are two well known examples of bacteria whose toxins that are often transmitted from bacteriophages?

Answer 20

• corynebacterium diptheriae

- vibrio cholerae

Question 21

What are transposable elements?

Answer 21

DNA seq that can jump from one position to another or one DNA molec to another

Question 22

What are IS elements?

Answer 22

• insertion sequences

- 1-3 kB in length, encode transposase protein required for transposition

Question 23

What is a transposon?

Answer 23

• transposable element that contains transposase as well as one or more genes
• can insert into plasmids which can then be transferred via conjugation to recipient cells

Question 24

What is an integron?

Answer 24

• DNA elements that encode site-specific recombinase
• have recognition region that allows other seq. with similar recognition regions to recombinate in
• elements that it acquires are called cassettes

Question 25

What are mechs of linear transmission of genetic variations?

Answer 25

• point mutations, DNA rearrangement

Question 26

What are mechs of horizontal transmission of genetic variation?

Answer 26

• transformation
• conjugation
• transduction

Question 27

What are 3 paths that could happen to DNA that comes into a bacterial cell?

Answer 27

• destruction [by nucleases or inherent instability]
• stabilization without replicative possibilities [ie circularization]
• integration by recombination

Question 28

What are 3 processes of integration?

Answer 28

• homologous recombination [RecA dependent]
• site specific recombination [phage mediated and through transposable elem]
• illegitimate recombination [nonhomologous]

Question 29

What makes VRSA resistant?

Answer 29

carry resistance on specific mobile genetic element

Question 30

What is cause of reduced daptomycin resistance in VISA?

Answer 30

mutation in rpoC [beta subunit of RNA ploymerase] and mutations in yyc gene cluser

Question 31

What makes VISA resistant?

Answer 31

• multiple mutation

35 mut at 31 loci causes differential gene expression of 224 genes