4: Microbial Growth III Flashcards
Binary Fission
parent cell spits into 2
each daughter has one old and one new strand of DNA
Division time
can take 20 minutes to over 24 hrs
type of growth caused by binary fission
Logarithmic growth (2^n, where n is number of generations)
each new cell becomes 2 new cells and so on
if unchecked at this rate… e coli could
exceed earth’s weight in 2 days
why haven’t bacteria eaten the world?
they eventually run out of food
Growth phases of bacteria
Lag phase
Log Phase
Stationary Phase
Death Phase
Lag phase
bacteria not growing, but adjusting to environment
preparing to use up food in environment
change protein expression to divide
Log phase
2^n
binary fission
growth unchecked
Stationary Phase
Running low on nutrients… only metabolize to stay alive
not growth, just maintenance of numbers
Death phase
Not enough food to maintain life
bacteria due
some cannibalize each other
Division time depends on…
Nutrient Source!
how nutrients affect bacterial growth
glucose is favored carbon source, bacteria grow quickly
lactose less preferred carbon source
what if you have 2 carbon sources (glucose and lactose)
glucose preferred, so used first, grow fast: steep line
glucose used: lag phase. take time to adapt to new environment (lactose). synthesize metabolites needed to metabolize glucose.
Lactose: another log phase
Ways to measure bacterial growth
Optical Density
Serial Dilution and Plating
Optical Density (OD)
based on light absorbance… 600 nm wavelength
instant measurement based on absorbancece
if lots of bacteria in the tube, they will scatter the light. more absorption of light, less light is transmitted
Drawback of OD
doesn’t tell you a number
Serial Dilution and Plating
gives you an actual number
DNA replication… the strands
are not identical
are complementary: matched by base pairing
know the sequence of 1 strand? figure out the other
DNA in bacteria
is a closed circle
2 replication forks, 2 leading and 2 lagging strand
the genetic info is carried…
on a single strand
base pairing
hydrogen bonds connect bases 3 bonds (GC) means more stable
sugar backbones of antiparallel strands
opposite! the double bonded oxygen on the phosphate is on the opposite side
5’: oxygen points toward top
3’: oxygen points toward bottom
what provides the energy for the reaction of adding a base?
hydrolysis of the phosphate bonds
how many DNA strands are around during replication
4… 2 parent, 2 new
DNA polymerase
adds free nucleotides to 3’ end. (copies DNA 5’ to 3’)
MUST have primer to start (RNA or DNA)
Proofreading ability
Can degrade RNA (RNase activity)
whats important about the free hydroxyl and where does it need to be?
3’ end
needs a primer
must be a free hydroxyl
helicase
opens RNA polymerase to put down primer
other enzymes stabilize the replication fork
lagging strand has to wait for DNA to be unwound to keep going
where MUST the new nucleotide be added
3’ END!!!!!!!
what adds the RNA primer so that DNA replication can start?
RNA polymerase
bacteria: EACH replication fork as a leading and lagging strand
1 origin of replication: 2 replication forks
they go in opposite directions
lots of things happen to happen (including unwinding) at the end to put them back together
Leading/Lagging with 2 forks
if its leading on one fork, its lagging on the other
what is PCR?
tool for targeting and amplifying specific DNA sequences
what is required for PCR
single stranded DNA “primers”
types of Horizontal Transfer of DNA
Recombination
Conjugation
Transduction
Transposition
Horizontal DNA transfer
acquisition of new DNA NOT from parent cell… usually smaller than chromosome
What enzyme does PCR use?
DNA Polymerase
verticle DNA transfer
DNA replication linked to cell division
why use PCR
to study genes… which are much smaller than the total DNA of the cell…
ex. shig toxin: 2,000 bases out of 5 million in e. coli
what do the DNA Primers do in PCR
are DESIGNED to direct DNA poly to a particular sequence and copy it a ton of times to make lots of copies
how are copies made using PCR (equation)
2^n
what does PCR do?
uses DNA polymerase in a very specific way. copy just the small piece you want
Recombination
(transformation)
uptake SIMILAR DNA sequence
DNA out there in environment… taken up and put into genome
NO VECTOR needed
“naked” DNA
Conjugation
Transfer DNA using type IV secretion (bacterial sex)
plasmid usually used to transfer DNA
DNA transferred BETWEEN bacteria
can carry antibiotic resistance plasmids between cells
Transduction
uptake of DNA by phage
movement by viruses
Transposition
jumping DNA
usually genes that have sequence on end that allow it to move around
usually within same cell…. but can move out of the crhomosome and become a plasmid
Conjugation… cell “types”
need a donor (F+) cell with a plasmid
and a recipient (F-) cell
donor replicates the plasmid then moves it into the recipient
Why does F+ make pili and F- doesn’t
plasmid of F+ codes for pili
F- doesn’t have plasmid (yet)
when injected with pili… F- can get the instructions for making pili
What else do we need to do to complete binary fission?
SPLIT THE CELL
how do baccili grow?
by elongation. gets to good size, repressors of DNA rep diluted so crhomosomes are copied and cells divide
How does it know how to grow?
growth is a function of increased cell mass
have enough cell mass (DNA, RNA, protein) to make a second cell
what else grows during DNA growth?
plasma membrane and cell wall
Contractile rings
form in middle of cell
directs cell division
scar helps hold bacillus in palce during new round of growth
Ring Scars
from where daughters divided previously
made of proteins
help new cell stay together and keep its shape
2 main proteins of contractile rings
FtsZ: like tublin
MreB: like actin
both PROTEINS
they may form spirals that may help rod shape stay in place
FtsZ
like tublin
MreB
like actin
DNA segregatin
just before contractile ring closes, DNA segregated into each daughter cell
replication and division are tightly linked
Antibotic Resistance Transfer
conjugation plasmids
Bacteriodes fragilis plsamid is a conjucation plasmid (RFT) that has resistance to 4 antibiotics
what is a main way antibiotic resistance genes are transferred?
plasmids
how transduction works
phage infects cell, puts its genome in bacterial chromosome for replication
sometimes the phage takes some bacterial DNA from the host and puts it into its next host
