17. Microbial Genetics I Flashcards
1
Q
core gene pool
A
chromosome that encodes for all of the necessary functions for survival of the bacteria
2
Q
flexible gene pool
A
- genes that allow the bacteria to be competitive
- mobile, can be passed between bacteria
- carried on: Genomic islands, islets, phages, plasmids, integrons, transposons.
3
Q
genomic islands
A
- gene blocks that have come from somewhere else, often encode virulence factors
- can code for properties like symbiosis.
4
Q
plasmids
A
Small, circular portions of DNA not associated with the nucleoid; carry antibiotic resistance
Can replicate independent of chromosome
5
Q
phages
A
bacterial viruses, play a large part in transferring virulence factors
6
Q
integrons
A
- gene capture units
- have 3 things: integrase, a promoter and an “at” site (that captures gene cassettes in the environment that have a corresponding at site)
- can’t replicate on their own
7
Q
transposons
A
- can move from one location on a chromosome to another (or on any replicon, like plasmids, phages); involved in antibiotic resistance
- must be associated with a replicon to replicate.
8
Q
transformation
A
free/naked DNA in the environment (from dead bacteria) is taken up by another bacteria and integrated through recombination mechanisms
9
Q
transduction
A
gene is transferred by a bacteriophage
10
Q
conjugation
A
transfer of genes via plasmids
11
Q
how does transformation occur?
A
- transforming DNA binds DNA binding proteins on cell surface (if cell is competent), uptake of ssDNA
- competence-specific single-stranded DNA binding proteins bind the DNA
- RecA proteins guide the single stranded DNA to the chromosome
- homologous recombination occurs, produces a transformed cell!
12
Q
what does homologous (general) recombination require?
A
- a large area of homology between the DNA sequences
- participation of host proteins
- it’s a non-additive process
13
Q
bacteriophages generally don’t have ___
A
membranous components (just a capsid)
14
Q
what are the two types of bacteriophages?
A
virulent and temperate
15
Q
virulent bacteriophages
A
- always enter the lytic cycle
- successful infection results in death of the infected cell
16
Q
temperate bacteriophages
A
can enter the lytic cycle or establish a quiescent relationship with the infected cell (lysogeny, integrates genome with host)
17
Q
upon integration, the phage is called a:
A
prophage
18
Q
a bacterial cell with a prophage is called a __
A
lysogenic cell
19
Q
ATT sequences
A
homologous sequences on the bacteria and bacteriophage (usually only one site on a bacteria)
20
Q
site specific recombination requires
A
- an ATT sequence
- an integrase
- it’s an additive process
21
Q
lysogenic conversion
A
the phage confers upon the bacteria a new phenotypic trait
22
Q
many bacterial toxigenic diseases (such as cholera) are caused by:
A
phages
23
Q
flexible gene pool arized from ____
A
horizontal gene transfer.
24
Q
4 important features of transformation that occurs via general recombination:
A
- requires RecA (finds homology and promotes integration of foreign DNA)
- requires extensive homology bw donor and recipient DNA
- is a replacement event, NOT additive
- cell must be in a state of competence to take up free DNA
25
What makes a cell competent? (required for transformation)
- cell secretes a protein, competent factor into environment, which can act in autocrine/paracrine fashion.
- CF interacts with a cell surface receptor to turn on expression of proteins that will allow the cell to take up transforming DNA.
26
_____ bacteria do not make competence factor, how do these become competent then?
Gm Negative -- instead recognizes environmental stress or is competent constitutively
27
in the first step of transformation, DNA recognized by the cell surface is ___ stranded, when it enters it is ____
dsDNA
| ssDNA
28
phages contain only ___ and ___
nucleic acid core (DNA/RNA) and protein encapsulation/nucleocapsid.
29
T4 has ___ host range, because ...
narrow, limited by the cell surface receptors it can bind to.
30
specialized transduction
a phage will transduce only specific regions of the bacterial chromosome
31
generalized transduction
random fragments of disintegrating host DNA are picked up by the phage during assembly; any gene can be transmitted this way
32
lytic cycle
a viral reproductive cycle in which copies of a virus are made within a host cell, which then bursts open, releasing new viruses
33
virulent phages
always follows the lytic cycle
34
lysogenic cycle
a viral reproductive cycle in which the viral DNA is added to the host cell's DNA and is copied along with the host cell's DNA
35
prophage
- phage DNA that's embedded in the host chromosome, maintained and replicated indefinitely. Occurs during lysogenic cycle of temperate phage.
- stably inherited by host progeny and noninfectious.
- REVERSIBLE relationship-- prophage can revert to vegetative state and develop lytically.
36
temperate phage reproduces through ___ cycle
A phage that is capable of reproducing by either the lytic or lysogenic cycle.
Lysogenic relationship is reversible, can revert to lytic cycle.
37
transducing phages
phage particles that contain a piece of bacterial chromosome instead of phage DNA inside the phage coat
38
What's a Hfr cell?
a bacterial cell with the F factor or F plasmid integrated into its chromosome (as an episome). Hfr = high frequency recombination
39
prophage only exists in which phage reproductive cycle?
in lysogenic cycle. in lytic cycle no prophage, the phage DNA is not integrated in host chromosome, it just takes over.
40
Which phage cycle takes longer to reproduce phage progeny?
lysogenic cycle, bc it depends on replication of the host and trigger that turns on lytic cycle.
41
ONLY after a phage undergoes ____ will all of that phage's progeny be considered transducing phages
```
Specialized Transduction
(Generalized = packaging problem; bacterial DNA NOT associated with viral, but packaged anyway
specialized = Bacterial DNA is connected to viral DNA and replicated in progeny)
```
42
bacterial conjugation in gram negative bacteria
1) F+ bacteria makes pilus with F- (recipient)
2) Pilus contracts to bring cells in contact
3) DNA transfer takes place
43
bacterial conjugation in gram positive bacteria
Positive = no Pilus involved
1. Cells come in contact via chemoattraction
2. Pheromones attract donor cell to recipient.
3. DNA is directly transferred upon contact
44
major difference between F+/F- mating and Hfr/F- mating
F+/F-: Plasmid is replicated and transferred to f- directly
Hfr: plasmid is first added to donor, then that DNA segment is transferred and added to f- (still f- after transfer bc no plasmid is transferred)
45
During ___ mating the plasmid genes AS WELL AS donor genes are integrated into the recipient's chromosome
HFR & F- mating
46
F' Plasmid
F plasmid can be excised from the Hfr cell, if excised imprecisely (taking small fragment of the Hfr chromosome), the resulting plasmid is called F' Plasmid.
47
generalized transduction:
- random fragments of bacterial chromosome accidently packaged into a viral capsid during lytic cycle (packaging mistake)
- any gene of the host bacterium can be transferred to recipient, but only bacterial genome is transferred (via transducing phage)
- doesn't require lysogeny
48
specialized transduction:
- specific host genes near the prophage are excised (result of imprecise excision)
- requires prophage and lysogeny
- bacterial fragments become part of viral genome and are transduced to subsequent hosts, along with phage DNA.
49
abortive transduction:
the transferred DNA is not integrated but often is able to temporarily survive and express
50
CRISPR
- clustered regularly interspaced short palindromic repeats
- viral DNA fragments are inserted into CRISPR array. Acquired immunity against subsequent viral infection and plasmid transfer.
- Absence of PAM within the CRISPR prevents autoimmunity
51
describe the two processes of bacterial conjugation
- 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 the two cells into close proximity
52
incompatibility groups
plasmids are selected based on these groups such that only one version exists in a population
-this is often used for taxonomy purposes
53
the __ is the plasmid origin used in transfer, the __ is the plasmid origin used in normal replication
oriT, oriV
54
how does a plasmid get integrated into the bacterial chromosome?
insertion sequences on the plasmid has counterparts on the bacterial chromosome, leading to homologous recombination
55
Hfr plasmid
a plasmid + bacterial chromosome
56
what are the mechanisms of plasmid specified resistance?
- 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)
57
Two types of resistance:
- intrinsically resistant-- already programmed into the basic organism
- selective/developed resistance-- all strains of an organism are initially sensitive to the challenge, over time a percentage of the strains develop resistance
58
what are the two types of resistance and what is the significance?
plasmid and chromosomal
- plasmid resistance can be transferred horizontally (rapid spread)
- chromosomal resistance is slower and only transferred to offspring
59
generalized recombination vs. site specific recombination
generalized recomb = transformation
| site specific recombination = transduction
