Lecture 7 Bacterial Genetics Flashcards
What is direct selection?
cells inoculated onto medium that supports growth of MUTANT but not PARENT
Antibiotic resistant mutants grow on what medium?
- parents do NOT
Medium with antibiotics
What is indirect selection?
isolates auxotroph from prototrophic parent stain
Why is indirect selection difficult
Since the parents grow on any medium which the auxotroph can also grow on
________ indirectly selects auxotrophs
Replica plating
in replica plating, all cells will form on ________ agar
Auxotrophs fail to grow on ________ agar
Nutrients
glucose-salts
Colonies that are missing on ________ agar allow identification of auxotrophs on master plate
glucose-salts
Penicillin enrichment does what?
selectively kills prototrophs
penicillin enrichment increases or decreases auxotrophs before replica plating?
increases
Penicillin kills only ________ cells
GRowing
prototrophs grow in ________ medium, auxotrophs do not
glucose-salts
________ added before cells are plated on nutrient agar to create master plate
Penicillinase
Carcinogens cause many cancers, most are ________
mutagens
Mutagens increase ________ of spontaneous reversions
low frequence
________ measures effect of chemical on reversion rate of histidine requiring salmonella auxotrophs
Ames test
If chemical is mutagenic, what happens to reversion rate in relation to control?
increases (more colonies grow)
What do recombinants do?
acquires genes from other cells by horizontal gene transfer
if you combine two strands that cannot grow on glucose salts medium, what mutants would occur?
spontaneous mutants are unlikely, simultaneous mutations are required
colonies that can grow on glucose salts medium require what?
acquired genes from other strains
What is DNA mediated transformation?
Naked DNA taken up from environment
What is transduction
DNA is transferred from one bacteria to another by bacteriophage
What is conjugation
DNA transfer during cell to cell contact
What is conjugation
DNA transfer during cell to cell contact
transferred DNA replicated only if it is a________ with origin of replication
Replicon
DNA fragments can be added to recipient chromosome by ________
Homologous recombination
In homologous recombination
Donor DNA replaces complementary region of recipient cellâs DNA
What are examples of replicons?
chromosomes, plasmids
transformation involves uptake of ________DNA
naked
What is naked DNA?
DNA is not within cell or virus
originates from cells that have burst or secreted
addition of DNase prevents transformation
For DNA mediated transformation, recipient cell must be ________
Competent
Most cells take up DNA regardless of ________
origin
Some cells only accept DNA from
closely related bacteria
In transduction, ________ infect bacterial cells
phages
How does the phage transfer DNA?
attaches to cell, injects its nucleic acid
phage enzymes cut bacterial DNA into small pieces
bacterial cell enzymes produce phage nucleic acid and coat
phage particles are released from bacteria
What is generalized transduction?
when a fragment of bacterial DNA enters the phage protein coat
- produces transducing particle
Transducing particle may attach to ________ and ________
another bacterial cell, inject DNA
- new DNA may be integrated into chromosome
What does a conjugative plasmid do?
Direct their own transfer
________ do not have to integrate into chromosome in conjugation
Replicons
In plasmid transfer for conjugation, what happens?
F pilus binds to receptor on recipient cell wall
F pilus contracts, pulls cells together
enzyme cuts plasmid at origin of transfer
single DNA strand is transferred
complementary strands synthesizes
Both cells are now F
In chromosome transfer for conjugation, what happens?
involves Hfr cells (high frequence of recombination
F plasmid is integrated into chromosome via homologous recombination
process is reversible
Fâ plasmid results when small piece of chromosome is removed with F plasmid DNA
Fâ plasmid is replicon, transferred to F cells
- carries bacterial DNA into new cells
What is Hfr cells?
high frequencey of recombination
F plasmid is integrated into chromosome via homologous recombination
What is core genome
common to all strands of the species
What is mobile gene pool
remaining strands that are not common to all strands of species
can move from one DNA molecule to another
What are included in the mobile gene pool?
plasmids, transposons, genomic islands, phage DNA
what are plasmids?
dsDNA with origin of replication
circular double stranded DNA
What is the function plasmids?
encode nonessential information, allow survival in particular environment
low-copy-number to high-copy-number
Plasmids have what host range?
narrow
Mobilizable plasmid requires _______ plasmid for transfer
Conjugative
What do resistant (R plasmids) plasmids
encode resistance to antimicrobial medication
R plasmids are conjugative plasmids with _______ host range
Broad
what do transposons do?
provide mechanism for moving DNA
Transposons can move into other _______ in the same cell
replicons
What does insertion sequence do
encodes only transposase enzyme, inverted repeats
_______ transposons include one or more genes
composite
Composite transposon integrate via what?
non-homologous recombination
What are genomic islands?
large DNA segments in genome that originated in other sepcies
In genomic islands, what are the nucleotides like?
very different from genome
G-C base pair ratio characteristic for each species
- if a large segment has a different G-C ratio, it indicates that the segment originated from a foreign source and was transferred through horizontal cell transfer
What are the characteristics encoded by genomic islands?
use of specific energy sources
acid tolerance
ability to cause disease
- pathogenicity islands
CRISPR systems include small segments of _______ DNA that recognize the specific DNA if it invades the cell agian
phage
in CRISPR, what happens in the first invasion?
complex of Cas proteins cut DNA into short segments
