Microbial Genetics Flashcards
Bacterial chromosome
single, large circular DNA molecule
contains all genes for survival
Plasmid
small, circular DNA molecule
replicated and transferred to daughter cells
Homologous recombination
exchange of DNA between two DNA molecules based on sequence similarity
What happens after homologous recombination takes place?
DNA incorporated into the chromosome are passed to daughter cells/become a permanent part of the genome
Transformation definition
uptake of free DNA from environment
purpose of transformation
allow bacteria to gain new traits quickly
Process of transformation
DNA is released into environment, gets actively imported into the bacterial cell. Homologous recominbation can occur.
What type of DNA does transformation use
any
Conjugation definition
DNA transfer directly from one bacteria to another via cell contact
purpose of conjugation
acquire new DNA
Process of conjugation
- mediated by fertility factor (F-factor)
- also has oriT
- single stranded DNA transferred from donor to recipient cell
tra operon
in the F-factor, encodes components of the sex pillus
oriT
origin of transfer. Where a single strand break occurs for transfer. in the F-factor
What happens in an F+ F- mating
transfer is unidirectional F- becomes F+ only a single strand is transferred no bacterial genes are transferred does not require homologous recombination
What happens in an Hfr F- mating
F- stays F-
requires homologous recombination
Transduction definition
transfer of bacterial DNA via bacteriophage
Generalized transduction
i. a lytic phage incorporates bacterial chromosomal DNA into its phage head
ii. when the phage infects another bacteria the DNA can be incorporated into its chromosome via homologous recombination
What type of DNA is used in generalized transduction
any
Specialized transduction
i. a lysogenic phage incorporates into the chromosome as a prophage
ii. an event (e.g. UV damage) leads to conversion to a lytic lifecycle
iii. upon excision from the genome, a small portion of the chromosome directly adjacent to where the phage was integrated is packaged into a phage head
Is homologous recombination used in transduction?
yes
Does transduction use free DNA?
no
Does transduction require cell to cell contact?
no
Intrinsic Antibiotic resistance
not transferable between bacteria
not increasing among bacterial populations
Chromosomal-mediated antibiotic resistance
arises through random mutations during replication
acquisition of DNA through horizontal gene transfer and incorporation into the genome via homologous recombination
Plasmid-Mediate antibiotic resistance
genes encoding antibiotic resistance located on a plasmid
These plasmids carry genes that encode proteins that degrade of modify an antibiotic or an efflux pump to pump the antibiotic out of cell
Has resistance factor
Resistance factor
conjugative plasmid
equivalent to F-factor (encodes all proteins needed for conjugation)
Transposons
mobile DNA elements that can transfer themselves (or a copy) from one molecule of DNA to another
present in both eukaryotic and bacterial cells, as well as viruses
What do transposons contain
indirect repeat sequences on each end
a single gene for transposase
contains a single or multiple antibiotic resistance genes
transposaae (TnpA)
enzyme required for transposon movement
Integrins
diverse group of genetic element
encode a site specific recombination system
can capture antibiotic resistance cassette
coordinately express them under control of integron promoter
resistance gene cassettes
carry genes that confer antibiotic resistance.
