Ch 4/11: Bacterial Sex Flashcards
What is horizontal gene transfer
non-sexual movement of genetic information between genomes
What is vertical gene transfer
the transfer of genetic material is from parents to offspring
What is the shape of DNA is most bacteria
circular
What components of DNA in bacteria
- bidirectional replication
- replication fork
How many origins in the DNA are there in bacteria
single
What happens at the replication fork in bacterial dna
DNA is unwound
What is the replicon in bacterial DNA
the entire region of DNA that is independently replicated from a single origin of replication
What is the shape of the DNA in archaea
circular
How many origins does archaea have in DNA
more than one (possible)
What is the pattern of chromosome in eukaryotes
linear
How many replication forks can eukaryotes have
many
What is the typical shape of bacterial chromosome
circular
How many chromosomes can bacteria have
one typically.
Example of bacteria that have more than 1 chromosomes
Cholera-causing bacteria has 2
Does bacteria have a nucleus
no
what do bacteria have instead of a nucleus
Nuclear region or nucleoid
what long is the bacterial chromosome
1mm
What type of twisting happens in bacterial DNA
supercoiled
what are plasmids
small, extrachromosomal DNA molecules,
autonomously replicating.
How many different plasmids can bacterial cells carry
several different, with few to many copies
what is the effect of gene transfer among bacteria
spreads useful genes among bacteria
what types of useful genes does gene transfer spread
1.antibiotic resistant genes
2. pathogenicity islands
3. genes to degrade special metabolites (?)
Where do antibiotic resistance genes spread
wherever antibiotics are overused. Eg, hospitals and farms
Why do pathogenicity islands encode genes
for the cell to act as pathogen
What difference typical E.coli and pathogenic Ecoli cause illness
Typical E.coli is found in gut and is useful. And pathogenic E.coli is harmful
What are pathogenicity Islands
are distinct genetic elements on the chromosomes of a large number of bacterial pathogens
What are metabolites
a substance formed in or necessary for metabolism.
what are some examples metabolites that gene transfer can degrade
oil slicks
What are the methods of genetic exchange
- transformation
- Conjugation
- transduction
What is transformation method
The non-specific acceptance by a bacterial
cell of small fragments of DNA from
the surrounding environment.
What facilitates transformation method of DNA
special DNA-binding proteins
on the cell wall that capture DNA
What type of cells use the transformation method for gene exchange
competent cells
what are competent cells
microbial cells that can readily take up foreign DNA from their surroundings through a process called transformation
When DNA is captured in transformation method, what happens to the new DNA
its incorporated into the chromosome
mention some places where transformation can be very useful
- biotechnology
- recombinant DNA Technology
When growing bacteria what types of strains can the bacteria have
- R strain - Rough
- S Strain - Smooth
What is the R strain
It is benign
what is S strain
it is virulent
Is the R strain protected?
No. It lacks a protective capsule
Is the S strain protected
Yes by a polysaccharide
What is the significance of having or not having a protective layer in S strain and R strain
R Strain: no protection = get recognized and destroyed by hosts immune system
S Strain: yes protection = prevents detection by hosts immune system
What is the capsule
Capsule is a gel-like
Covering made chiefly
of polysaccharides.
what is the capsule associated with
virulent
What does the capsule help resist
phagocytosis
What is phagocytosis
important process for nutrition in unicellular organisms
Is the capsule genetic?
Yes. Its genetically encoded
what is conjugation
Transfer of DNA from one
bacterium to another by cellular contact
In conjugation, what direction does the DNA move when moving from one bacteria to the other
DNA moves unidirectionally from one
bacterium (the donor), to another bacterium,
(the recipient).
What states are the genes involved in genetic transfer exist in the donor
- On a F Plasmid
- On a F’ plasmid
- Integrated into bacterial chromosome Hfr
What is bacterial chromosome Hfr
High frequency of recombination. A strain of bacteria that has incorporated an F factor into its chromosome and can then transfer the chromosome during conjugation
Through what medium does conjugation occur in bacteria
through a cytoplasmic bridge
What is F+ cell
the donor (of gene)
What is the F- cell
the acceptor (of gene)
What is the type IC secretion system
pilus (? – textb)
for bacterial sex where are the pilus proteins encoded
on F Factor
On what site does the pilus protein encoding start
oriT
in bacterial sex, in the recipient cell, what does the transferred DNA form
forms a new plasmid
After the bacterial sex, what happens to the “female” cells
they become “male” cells i.e. they’re able to transfer to DNA
how many states do transfer genes exist in
3
How many forms do genetic transfers occur in
3
What are the forms in which genetic transfers occurs
- F+ —–> F-
- F’ ——> F-
- Hfr ——> F-
What is the F+ donor
The donor “male” has a fertility factor (F+) that is itself heritable.
What is the F’ donor
What is the F Plasmid
fertility factor
What is the structure of the F Plasmid
circular DNA molecule with one region that contains the genes that regulate DNA replication
What is the large region of DNA in F Plasmid called
tra region
What is the tra region
it contains genes that encode transfer functions
What is the F’ Factor
its the fertility factor plasmid that contains extra genes (in addition to genes for pilus and transfer)
What happens to the extra genes that F’ has
get transferred to recipient
What is the Hfr plasmid
in Hfr the F factor integrates on the bacterial chromosomes
What does the Hfr transfer to the recipient
tried to transfer the entire chromosome
Can Hfr determine the order of genes on chromosome
yes
Can Hfr transfer genes in order
yes
What is the name of Hfr
high frequency of recombination
In the production of F’ and Hfr, what region loops out of the chromosome
the F Factor loops out and takes a portion of the bacterial chromosome
What does a single crossover generate
F’ which includes bacterial chromosome
In terms of gene transfer, what are F plasmids responsible for
antibiotic resistance
F plasmids that harbours genes for antibiotic resistance are called
R factors
how many antibiotic resistance genes can a single F’ plasmid harbour
several
Bacteria resistance to several antibiotics are called
MDRs or multidrug-resistant bacteria
___ Plasmid can also carry genes encoding traits that play a role in disease
F’
example of subtance that plays a role in disease whose gene F’ plasmid carries
toxins
What are R Factors
F’ plasmids that contain both transfer tra genes and genes for antibiotic resistance
Can MDR bacteria transfer the resistance during conjugation
yes!
What happens in transduction
a bacterial virus (bacteriophage) transfers
DNA from one cell to another
what is a bacterial virus called
bacteriophage
viruses that inject their DNA into cell are called
bacteriophage
bacteriophage pack DNA into viral ___
capsid
Can the the bacteriophage package bacterial DNA by mistake
Yes
in order for newly acquired DNA to be incorporated what is required
has to go through recombination
What happens if the newly acquired dna doesn’t get incorporated
youll have very transient diploids
What type of gene transfer is important for evolution
horizontal gene transfer
are genes be transferred to the same specie or different species
both
what are mutagens
Anything that causes a mutation (a change in the DNA of a cell)
Most carcinogens are also ___
mutagens
tests for mutagenicity are used as screen for ______ potential
carcinogenic
What is an examples of an carcinogenic test
Ames test
what are auxotrophs
a group of organisms that lost the ability to synthesize certain substances required for their growth owing to the presence of mutations
what kind of strain does the ames test use
uses bacterial strain auxotrophic for histidine i.e cannot grow unless histidine is supplied
What does it mean to be auxotrophic for something
the organism has a mutation in that thing and cant grow unless it is supplied with that thing
On the plate medium for ames test, if the mutagen added to the plate causes reversion, what does it mean
reversion means that the auxotrophic mutagen changed to its normal form — this is a rare mutation
on the plate medium for ames test, what does it mean if more colonies are grown
more colonies = stronger mutagen
what does cancer result from
multiple mutations
DNA transfer occurs typically in one direction, which is
donor to recipient
3 mechanisms of horizontal gene transfer
- transformation
- transduction
- conjugation
What some origins of replication
- a plamid
- phage genome
what is meant by origin of replication
An origin of replication is a sequence of DNA at which replication is initiated on a chromosome, plasmid or virus.
what are the 3 fates that horizontally transferred DNA can face
- it degrades by recipient restriction enzymes or dna destruction systems
- may replication by itself if it has origin of replication
- it may recombine with recipient cell chromomsome
