M8: Bacterial Genetics & Antimicrobial Resistance Flashcards Preview

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Flashcards in M8: Bacterial Genetics & Antimicrobial Resistance Deck (22)
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1
Q

Horizontal Gene Transfer (HGT) in Bacteria:

Definition

Three main mechanisms of HGT

Different types of bacteria are resistant to a number of antibiotics because they contain _

These as well as other _ can be transferred between bacteria

A

the transfer of DNA from one bacterium to another which is not its offspring

transformation, transduction, and conjugation

antibiotic resistance genes

bacterial genes

2
Q

Genetic Transformation:

Definition

Natural Transformation occurs in bacteria such as _, _, and _ which produce a protein called the _

_ enters the recipient cell & is integrated into the recipient DNA by _ mediated by the _ protein

This results in _

A

the process by which a recipient cell takes up naked DNA released by a donor cell

Streptococcus, Haemophilus and Neisseria
competence factor

a single strand (ss) of DNA
homologous recombination
RecA

the replacement of the recipient DNA by the donor DNA

3
Q

Transduction:

Gene transfer from a donor cell to a recipient cell by a _

A donor cell is infected by a _. This _ in the cell and _ host DNA. These particles are assembled and some of them contain small pieces of _.

Upon reinfection of a bacterial cell, the DNA from the original cell is _ into the recipient chromosome by _

Any _ present in the donor cell can also be transferred to the recipient cell

A

bacterial virus (bacteriophage)

bacterial virus (phage)
replicates
degrades
bacterial DNA

integrated
homologous recombination

plasmid DNA

4
Q

Conjugation:

Gene transfer between a donor and a recipient cell through _

Male cells differ from female cells by possessing _ elements termed _

Such plasmids contain genes that enable them to _

_ plasmids are found in both Gram-negative and Gram-positive bacteria, and _ is the most common form of horizontal gene transfer in bacteria

A

direct physical contact

extrachromosomal DNA
conjugative plasmids

transfer copies of themselves to another bacterium

Conjugative
conjugation

5
Q

Bacterial Plasmids:

Plasmids are _ elements that exist in bacterial cells and have the ability to confer _ on the bacterial cell

They are usually (circular / linear), (single / double)-stranded DNA molecules, although (circular / linear) plasmids are also found in nature

Plasmids frequently contain _ genes and are the main reason for the spread of _ bacteria in nature

Plasmids are very (stable / unstable) and (rarely / often) lost from bacterial cells

All plasmids carry genes that allow them to _ independently of the bacterial chromosome

Plasmids also require _ and _ for replication

A

small extra chromosomal
new genetic properties

circular
doubled
linear

drug resistance
antibiotic resistant

stable
rarely

replicate

host proteins
enzymes

6
Q

Replication of Bacterial Plasmids:

A plasmid replicon consists of: (3)

A

origin
rep gene
copy control gene (cop)

7
Q

Replication of Bacterial Plasmids:

A plasmid replicon consists of:

origin - the site of _ of replication

rep gene - encodes an _ protein that is required for plasmid replication

copy control gene (cop) - involved in controlling the _ and _ of a plasmid

A

initiation

initiator

replication and copy number

8
Q

Replication of Bacterial Plasmids:

Copy number - The number of _ per _ in a cell

The copy number for a given plasmid is (fixed / variable)

A

plasmid molecules
chromosome

fixed

9
Q

Replication of Bacterial Plasmids:

Large plasmids, usually (conjugative / non-conjugative), have a (high / low) copy number (# per chromosome)

Small plasmids, usually (conjugative / non-conjugative), have (higher / lower) copy numbers (# per chromosome)

A

conjugative
low
1-2

non-conjugative
higher
more than 10

10
Q

Replication of Bacterial Plasmids:

Several different plasmids can be present in the same host cell and these _ plasmids are maintained and replicated _ of each other

_ plasmids are unable to coexist stably in descendants of the same host cell

A

compatible
independently

Incompatible

11
Q

Conjugative plasmids:

Many plasmids such as the _ plasmids (termed _ or _) initiate their own transfer by cell to cell contact

Many _ plasmids can also be mobilized by conjugative plasmids present in the same cell

R plasmids usually contain several _ genes, have a broad _, and can transfer between different _

They are found in almost all major _ and can confer resistance to almost all the _

A

resistance
R plasmids or R factors

non-conjugative

antibiotic resistance
host range
bacterial species

human pathogens
antibiotics

12
Q

R-Plasmids (R-Factors):

R plasmids contain _ genes (encoding the sex pilus through which DNA is transferred from a donor to a recipient cell), _ genes that are usually clustered, and the _ region

_ represents the site where the transfer of the R plasmid during conjugation is initiated

This is nicked by a _ during the initiation of DNA transfer

During conjugation, a (single / double) strand of DNA is transferred to the recipient cell starting from its (3’ / 5’) end

DNA replication in both the donor and recipient cells regenerates the (single / double)-stranded plasmid DNA

R factors also contain _ sequences and _

A

tra
drug resistance
replication

oriT
nickase

single
5’

double

insertion
transposons

13
Q

Virulence Plasmids:

Carry genes that encode _ and other _

Examples: Plasmid pXO1 of _ encodes the anthrax toxin proteins while plasmid pXO2 contains genes required for _

Plasmids also contain the tetanus toxin gene in _, and invasion genes in _

A

toxins
virulence factors

Bacillus anthracis
capsule biosynthesis

Clostridium tetani
Yersinia

14
Q

Origin of Antibiotic Resistance Genes and Evolution of R Plasmids:

Many _ producing bacteria such as _ are the source of the antibiotic resistance genes found in other organisms

However, many “_” genes may have evolved to encode proteins and enzymes involved in drug resistance

There is a substantial pool of antibiotic resistance genes in _ and such genes (can / cannot) be transferred between different bacteria

Complex R plasmids can evolve from the insertion of _ elements and “_” (carrying antibiotic resistance genes) into plasmids

_ are mobile DNA elements encoding an _ and may carry additional genes such as those encoding antibiotic resistance

A

antibiotic
Streptomyces

housekeeping

nature
can

transposable
integrons

Integrons
integrase

15
Q

Transposable Elements:
Definition:

A transposon (Tn) is a genetic element (a specific DNA segment) that can _

Tns generally carry one or more genes encoding _, _, etc. to the host cell

Tns are normal constituents of _ and _

Transposons (occur / do not occur) independently in a cell, and are (always / never) found as part of a genome

Insertion Sequences and transposons contain _ at their ends

A

repeatedly insert at many different sites in a genome

drug-resistance, toxin production

bacterial chromosomes and plasmids

do not occur
always

inverted repeats (IRs)

16
Q

Transposable Elements:
Classification:

Transposable elements are usually divided into two groups (2)

A

Insertion Sequences

Transposons

17
Q

Transposable Elements:
Classification:

Transposable elements are usually divided into two groups

a) Insertion Sequences are (large / small) elements (750-1500 base pairs) that carry only those genes that are required for their _
b) Transposons are genetic elements (usually (larger / smaller) than 5 kilobases) that carry genes required for their _ as well as additional genes that specify a _ such as _, _, etc.

Composite transposons carry _ at their ends, and typically an _ gene.

A

small
movement

larger
movement
phenotype
antibiotic resistance, toxin production

insertion sequences
antibiotic resistance

18
Q

Transposable Elements:

The transposon Tn3 consists of: (4)

A

tnpA gene
tnpR gene
Amp^r gene
Inverted repeats

19
Q

Transposable Elements:
The transposon Tn3 consists of:

tnpA gene which encodes the _ protein that is required for transposition

tnpR gene which encodes the _ of transposition

Ampr gene (_) that encodes _ which makes bacteria resistant to _

Inverted repeats (IRs): The _ at one end of a transposon is repeated at the other end (in _ orientation). The IRs are absolutely necessary for transposition.

A

transposase

repressor

bla
β-lactamase
ampicillin

DNA sequence
inverted

20
Q

Transposable Elements:
Mechanism of transposition:

Transposition can be either _ or _ (_)

A

replicative

conservative (nonreplicative)

21
Q

Transposable Elements:
Mechanism of transposition:

Replicative transposition involves _ replication of the transposon and results in the _

Nonreplicative transposition results in the _ of the transposon at the _

A

semiconservative
duplication of the Tn element

simple insertion
target site

22
Q

Transposable Elements:
Mechanism of transposition:

Transposition can be _ or _, i.e., can take place within the same genome or between two genomes.

Many R-factors contain a number of different _, carrying several _ genes.

A

intermolecular
intramolecular

transposons
antibiotic resistance