Bacterial Genetics (#2) Flashcards
the _______ is the location of the chrosome and associated proteins in bacteria
nuceloid
the nucleoid is an ________ shaped region, that is usually not _______ bound
irregularly; membrane
exception of bacteria where nucloids DO have a lipid bilayer/membrane around the chormosome
plantomyces (in 2 genera of family)
bacterial nucleoid genome:
usually one, circular, dsDNA molecule
bacterial nucloeids are tightly coiled, but have some _____ edges like a ball of yan
loose
what kind of cells have nuceloids in general?
prokaryotic cells
extra-chromosomal DNA
plasmids
plasmids usually have what kind of genome?
small, closed circular dsDNA
plasmids exist and replicate _________ of chromosome; own replication functions
independently
T/F: plasmids double every time the cell divides and is split up evenly between the cells
false (uneven inheritance/division can occur)
plasmids contain few _____
genes
the few genes that plasmids do contain are __________ and ____________ genes
non-essential; housekeeping genes
the non-essential genes that plasmids contain could be selectively ________
advantageous (like a bag of goodies)
plasmids are a lot ______ than chromosomes
smaller
plasmids increase _______ of a bacteria/organism
diversity
T/F: bacteria can’t survive without plasmids
false (they can, but plasmids can be advantageous)
plasmids can be _________ (make lots of copies) or _________
high-copy # or low-copy #
plasmids can be easily _____ if cells don’t use it are are less _____ than traits found on chromosomes
lost; stable
plasmids that CAN incorporate onto the chromosome so they don’t get lsot
episomes
example of advantages bacteria can acquire from plasmids (2):
- antibiotic resistance
- have lactase — use lactose as a carbon source
DNA is composed of 4 ______ , or _______
nucleotides; bases
who came up with the fact that DNA is the genetic material (3)?
- Griffith
- Avery, MacLeod, and McCarthy
- Hershey and Chase
came up with Transforming Principle; smooth (had capsule) vs rough cell experiment
Griffith
disocovered that bacteriophage T2’s genome was DNA
Hershey and Chase
who discovered the STRUCTURE of DNA?
Watson and Crick
DNA is composed of _____ base pairs, with ________ strands
nitrogenous; antiparallel
DNA segment that codes for a polypeptide, rRNA, or tRNA
gene
when writing out genes, they are ________ and _________
lowercase + italicised (ex: hisC)
specific set of genes an organism possesses (the nucleotide sequence)
genotype
set of OBSERVABLE characteristics
phenotype (p for picture)
when writing out phenotypes, you use what?
+ or - signs (His+ or His-)
strain isolated from nature; considered “non-mutant” form
wild-type strain
stable, heritable change in nucleotide sequence; genotype is altered; may or may not have an effect on the phenotype of an organism
mutation
mutation that doesn’t alter the phenotype; goes unnoticed
silent mutation
how do you write out mutations?
italicized, designation of gene + order of mutation (hisC1, hisC2, etc)
types of mutations (2):
- forward
- reverse
most prevalent form of a gene
wild-type
type of mutation: wild-type to mutant form
forward mutation
example of forward mutation:
prototroph —> auxotroph
nutritional mutant
auxotroph
type of mutation: mutant PHENOTYPE to wild-type PHENOTYPE
reverse mutation
example of reverse mutation:
auxotroph –> prototroph
products of reverse mutatations =
revertants
ways to get revertants (2):
- same-site revertants
- second-site revertants
way to get revertant: base pairs that changed are changed back to its ORIGINAL (ex: A-T to C-G back to A-T)
same-site revertant
way to get revertant: suppressor mutation; still have mutations, but composited with another mutation somewhere else; changes it back to original wild-type phenotype
second-site revertant
non-nutritional mutant
prototroph
detecting mutants via observation
screening
mutations that confer some type of advantage to the organisms that possess them (ex: drug resistance)
selectable mutations
selectable mutations _______ screening time
decrease
placing organisms under conditions where the growth of those with a particular GENOTYPE will be favored; only allows MUTANTS to grow
selection
detection of nutritional auxotrophs (2):
1) pick and transfer colonies to fresh medium (complete + selective)
2) incubate and examine plates
2 type of mediums
- complete
- selective
type of medium: ALL colonies grow
complete
type of medium: mutants to NOT grow; missing growth factor (ex: histodine) that auxotrophic mutants need to grow
selective
looking at what did NOT grow on the selective medium
negative selection
missing colonies are _________ _________; look back at complete medium to use them
histodine auxotrophs
______ _____ procedure may also be used to detect nutritional auxotrophs
replica plating
HGT =
horizontal gene transfer
________ can do horizontal gene transfer, but we can’t
bacteria
horizontal gene transfer increase _______ quickly; allows bacteria to adapt faster
diversity
3 methods of HGT:
1) transformation
2) transduction
3) conjugation
method of HGT: donor DNA from a dead cell (naked DNA outside of the cell) to a recipient cell which then expresses it
transformation
what kind of DNA is transformed in transformation?
naked DNA (outside of the cell)
method of HGT: virus makes a mistake and packages DNA from its original host cell and releases it to another bacterium; transfer BACTERIAL DNA, not viral
transduction
method of HGT: a donor cell that can make a sex pilus that attaches to recipient cell; sends a copy of a PLASMID to contains the traits for this method
conjucation
plasmid used in conjugation
fertility plasmid (F plasmid)
there are cases where ______ transfer occurs along with plasmid transfer in conjugation
chromosome
T/F: horizontal gene transfer always works
false
fates of donor DNA during horizontal gene transfer
- host restriction
- donor DNA self-replicates (ex: plasmid)
- donor DNA self-replicates
- integration of donor DNA
fate of donor DNA during HCG: restriction endonucelase cuts up foreign DNA and then cell reproduces with NO stable recombinants
host restriction
enzyme that cuts up foreign DNA; can be advantageous to cut up viral DNA; specific where it cuts at; prevents cells from being infected with bad DNA
restriction endonuclease
fate of donor DNA during HCG: donor DNA just hangs out and eventually gets lost in a daughter cell; recipient reproduces but donor DNA does not – NO stable recombinants
Donor DNA cannot self-replicate
fate of donor DNA during HCG: forms a plasmid and reproduces; produces population of STABLE recombinants (traits can be expressed)
Donor DNA self-replicates
fate of donor DNA during HCG: DNA goes onto the chromosome; chromosome replicates with DNA; produces a population of STABLE recombinants
Integration of donor DNA
one or more nucleic acid molecules are rearranged or combined to produce a NEW nucleotide sequence
genetic recombination
types of recombination (2):
- homologous
- heterologous
type of recombination: usually involves a reciprocal exchange between a pair of DNA molecules with the SAME (or nearly the same) nucleotide sequence; one type
homologous recombination
recombination leads to new ______
genes
in homologous recombination, DNA strands break and reunite leading to a _________
“crossover”
steps of homologous recombination (4):
1) DNA strand is nicked
2) SSB protein and RecA protein complex formed
3) recipient DNA invaded
4) crossover leads to exchange which is then ligated to form two recombinant DNA molecules
for homologous recombination to occur, bacteria has to be _______ positive (have this protein)
RecA+
protein that pulls foreign DNA into double helix (like a train); if enough base pairs match, strands will try to bond (brakes on train) and ends in homo. recombination
RecA+
number of matching base pairs between recipient and foreign DNA in LOW LEVEL recombination
20-40 matching base pairs
number of matching base pairs between recipient and foreign DNA required in HIGH LEVEL recombination
> 165 pairs
enzyme that determines which way crossing over occurs
resolvase
protein that binds to single strand of DNA and protects it from being cut up further
SSB (single strand binding protein)
Trp- cells dont make _______ on their own
tryptophan
if Trp- cell are incoluated onto agar medium lacking tryptophan, what happens?
no growth
if DNA from Trp+ cells are introduced to Trp- cells and incoluated onto agar medium lacking tryptophan, what happens?
recombinants form colonies
uptake of naked DNA by a competent cell followed by incorportation of the DNA into the recipient cell’s genome
transformation
transformation can be _______ or _______
natural or artificial
transformation can also occur with a ________
plasmid
how is transformation induced artificially (2)?
- heat shock
- electroporation (uses jolts of electricity)
cell that can bind to DNA and bring it into the cell
competent cell
competence can alter based on __________ and _________; my not be for long
species + environment
the DNA incorporated into the recipient cell’s genome during transformation much be able to ________
replicate
transfer of DNA from one cell to another by a BACTERIOPHAGE; mistake phage makes
transduction
2 mods of transduction:
1) generalized transduction
2) specialized transduction
mode of transduction: DNA from any portion of the host genome is packaged inside the virion
generalized transduction
mode of transduction: DNA from a SPECIFIC region of the host chromosome is integrated directly into the virus genome
specialized transduction
generalized transduction only occur during which cycle?
lytic cycle
during viral assembly in generalized transduction, fragment of host DNA are mistakenly packaged into the phage HEAD, called the _____ _________
transducing particle
the transducing particle in generalized transduction is _________
defective (virus cannot cause a normal viral infection anymore)
cuts genome to correct size for virions during generalized transduction; bacterial DNA then gets into virus
cackatomer
the transducing PARTICLE contains what kind of DNA?
donor cell DNA (bacterial)
the transduced recipient cell contains what kind of DNA?
viral DNA
mode of transduction: carried out by temperate phages that have established LYSOGENY; DNA incorporates itself on bacterial chromosome
specialized transduction
specialized transduction occur when __________ is incorrectly excised
prophage
steps of specialized transduction (4):
1) induction
2a) phage DNA circularizes and detaches from host DNA
2b) a portion of host DNA is exchanged for phage DNA (Rare Event)
3) detached DNA replicates
4) phage replication is completed and cell lyses
during normal induction in transduction, a _______ comes off the chromosome and goes into the lytic cycle
prophage
during the NORAML event in specialized transduction, the phage DNA circularized and detaches from host DNA using __________
exionase
during the rare event in specialized transduction, a mistake is made during ___________ and exionase cuts out ________ genes and ______ genes
induction; galactose genes + adjacent genes
during the rare event in specialized transduction, every single viral genome has ________ genes and are _______
galactose; defective
all defective phages that carry galactose genes in specialized transduction
λdgal
λdgal stands for
λ: lambda
d: defective
gal: carries galactose gene
steps of bacterial conjugation (5):
1) the pilus retracts
2) cell pairs are stabilized; F plasmid nicked in one strand
3) transfer of one strand from F+ to F- cell; F plasmid simultaneously replicated in F+ cell
4) synthesis of complementary strand begins in the recipient cell
5) completion of DNA transfer and synthesis; cells separate
genes for conjugation are usually found on _______
plasmids
donor cell; carry plasmid
F+ cell
recipient cell WITHOUT plasmid
F- cell
region on plasmid that contains genes for conjugation
tra region
what does “ori” mean on the F plasmid?
original of replication
what does “IS3” mean on the F plasmid?
insertion sequence
what does “Tn1000” mean on the F plasmid?
transposon
2 origin of replications of F plasmid:
- oriT
- oriV
origin of replication on F plasmid: origin of replication when it is going into the other cell for rolling circle replication; where you break plasmid to go into other cell; where DNA polymerase binds when conjugation occurs
oriT
origin of replication on F plasmid: origin for vegetative plasmid; NORMAL origin of replication; where DNA polymerase would bind
oriV
what does oriT stand for?
origin of TRANSFER
when the single strand rolls up and is replicated to get a dsDNA plasmid in other cell during conjugation
rolling circle replication
a ________ strand of DNA is transferred from the F+ to F- cell
single (sends a copy of a plasmid)
T/F: F plasmids can carry other genes besides those for conjugation
true (ex: antibiotic resistance)
