Exam 3 Chapter 6 Flashcards
bacterial transformation
uptake of foreign DNA by a bacteria
(sometimes must make cells more competent before they can take in DNA)
transduction
viral transmission
some viruses only affect bacteria because
their spike factors can only bind to receptors on bacterial surfaces
prokaryotes have no ______
genetic diversity; each cell gets the same chromosome after replication
horizontal transmission
transfer of DNA via conjugation, transformation, or transduction
no cell division
leads to genetic diversity
vertical transmission
passage of DNA information from one generation to the next via binary fission
ex. circular chromosome replicates itself exactly (w/ possible mutation)
where are the most necessary genes in bacteria
in the main chromosome
where are “extra” genes or “genes of interest” like AMPR found in bacteria
on plasmids
plasmids
smaller, circular, contain nonessential genes
conjugation leads to _______
partial genome transfer
recombination could lead to genetic diversity (double crossing over allows DNA exchange at points of contact)
transformation leads to _______
partial genome transfer by DNA uptake
very rare
viral transduction
a piece of bacterial genome enters the viral DNA - transferred to new bacteria - recombination can occur
very rare
function of DNA poly I (bacteria)
exonuclease activity removes RNA primer, replaces it with newly synthesized DNA
function of DNA poly III (bacteria)
main enzyme that synthesizes new DNA in the 5’ to 3’ direction
requirement of conjunction
sex pilus - protein bridge creating contact between cells for plasmids to travel through
Lederberg & Tatum
1946
discovered sex-like process of conjugation by studying 2 E. coli strains w. different auxotrophic mutations
auxotroph
mutant type
usually 1 mutation
cannot grow on minimal media
prototroph
wild type
no genetic defects
can grown on regular OR minimal media
minimal media
bare necessities for bacteria to grow: water, inorganic salts, sometimes a carbon source
complex/complete media
has all the nutrients.cofactors for non-fastidious organisms
nutrients in complex media
TSA, TSB, LB, NA, NB (nutrient agar/broth)
carbon, nitrogen, water
effect of lipoic acid mutation (Lip A)
no acetyl CoA
no Krebs cycle/ETP
shift in global gene expression
genes will be up- and down-regulated in order to survive
process of Lederberg and Tatum’s experiment
- mixed A and B
- formed wild type
- first test tube: negative for methionine, biotin - positive for threonine, leucine, thimine
–> grew no colonies on minimal media - second test tube: mixture produced prototrophic colonies which made met, bio, thr, leu, thi on minimal media
- third test tube: negative for thr, leu, thi - positive for met, bio
–> grew no colonies on minimal media
conclusion: mixing two auxotrophic mutants with different abilities to produce AAs would allow them to combine to form prototrophic wildtype cells that can produce all AAs
Davis and his U-shaped tube
to prove that substances were not leaking from one cell to the next, Davis used a U-shaped tube with a thin filter to separate the two strains
only substances could pass through - cells could not touch - no prototrophic cells were found
structure of U-shaped tube
porous cotton plug above side with strain A
fine filter
pressure/suction apparatus above side with strain B
William Hayes
1953 - discovered the fertility factor (F)
fertility factor
plasmid responsible for genetic transfer
transfer of genes in E. coli conjugation
not reciprocal
F plasmids from F+ donor cells are transmitted to F- to recipient cells by rolling circle replication
bacterial chromosome is not transferred
tra genes
transfer genes found in plasmids
rolling circle replication
Rep protein binds at DSO (double strand origin) and cleaves the + strand
DNA poly III begins to create new strand around - strand for donor cell
Rep protein moves the + strand into the recipient bacteria which makes its own new strand
fertility factor
a plasmid
non-essential circular DNA molecule
has an origin of replication - can replicate independently of its host chromosome
F factor directs synthesis of
sex pilus to bring cells closer together
Rep A protein has ________ activity
endonuclease: cuts DNA strand
og plasmid after rolling circle replication
old - strand, new + strand
Luca Cavalli-Sforza
discovered Hfr strain - derivative of F+ strain
Hfr
High frequency of recombination - the plasmid has been recombined into the chromosome (F is integrated)
is the F+ factor transferred in Hfr strain
very rarely
Lederberg and Tatum discovered
conjugation
Hfr strains and F- strains will almost never…
become F+ strains
full plasmid transfer is rare
plasmid would theoretically be the last to enter the F- cell
and sex pilus would break down before the plasmid would be transferred
crossovers integrate parts of the transferred donor fragment
origin reaches F cell first, followed by genes in order
transferred fragment is converted into a double helix in the exconjugant
double crossover inserts donor DNA in the recombinant
how to determine the distance between genes
time the arrival of genes in the F- cell by stopping and starting recombination process
exogenote
foreign DNA in the exconjugant
endogenote
original DNA of the exconjugant (F- strand receiving DNA)
results of recombination with Hfr
F- cell gains the ability to express the genes in recombined DNA
Elie Wollman and Francois Jacob
discovered linear transmission of ssDNA begins from a fixed point (origin - O)
each donor allele first appears in the F- recipient at:
a specific time, in a specific sequence
if a gene is farther from O on the strand
it will be transferred later
later donor alleles are present in fewer recipient cells because
the transfer process generally stops before all genes are transferred
timing entry of Hfr alleles entry into F- recipient is used to
make a chromosome map
who figured out bacterial transformation
Frederick Griffith 1928
possible sources of DNA for transformation
same species or other species
dead or living cells
purpose of DNA-degrading enzyme in bacterial DNA uptake
found where DNA passes through cell membrane
has endonuclease activity
defense mechanism to recognize specific sequences and cut free DNA
why don’t DNA-degrading enzymes cut the bacteria’s own DNA
specific methylation patterns
number of classifications of virus genomes
7
what is viral genome classification based on
how they produce mRNA
bacteriophage
virus that only infects bacteria
lytic cycle
1) phage tail fibers have spike proteins
and attach to bacteria surface receptors
2) phage inserts its genome - degrades host DNA
3) directs cellular machinery (DNA poly III) in cell to make many copies of phage DNA and sheath components
4) more phages are assembled
5) cell lyses and phages are released
apoptosis
release of phages from lysed cell
transduction
phage takes DNA from 1 bacterial cell and it is recombined into the DNA of another cell
phage assembly
1) head (containing DNA)
2) tails
3) tail fibers (w/ spike proteins)
lysogenic cycle
1) phage DNA inserted into bacteria
2) phage DNA circularizes
3) phage DNA integrates into the bacterial chromosome, becomes a prophage
4) bacterium reproduces normally - prophage is copied into daughter cells
5) many cell divisions -> lots of infected bacteria
what happens if prophage exits bacterial chromosome
lytic cycle is initiated
transduction can happen to
genes on any of the cut-up parts of the host genome
