prokaryotic cell biology Flashcards
organisation of a prokaryote
- cell wall
- plasma mem.
- cytoplasm
- ribosomes
- pili
- nucleoid
- flagellum
what are plantomycetes
true bacteria that contain a nuclear envelope
members of planctomycetes show
true compartmentalisation
–> DNA is surrounded by a double lipid bilayer–> like the nuclear envelope of eukaryotes
organelle
a structure or part that is enclosed with its own mem., inside a cell and has a particular function
organelles are found only in
eukaryotic cells and are absent from he cell of prokaryotes such as bacteria
magnetosomes
- navigate along magnetic filed
- can detect magnetic field and contain a ‘compass’ that detects the magnetic field of earth
magentosomes are found wihtin
gram negative bacyeria
first bacteria discovered two have magentosomes
Magnetospirilium magnetotacticum found by richard blakemore
-contains iron mineral and crystal that are magnetic and are called magnetosomes
bacteria use the magnetosomes for
mangnetotaxis
formation of magentosomes is a stepwise process
step 1: invagination of cytoplasmic men
stem 2: accumulation of ferrous iron
step 3: nucleation of magnetosome formation
what shows a similar fold in eukaryotes and prokaryotes
F-actin and prokaryotic actin-like protein filaments
- same fold , but only 15% identity between MreB and eukaryotic actin
- Both bind ATP and both polymerise
which structures are very similar
ParM, MreB and actin
Actin
- eukaryotes
- cytoskeleton
- 100% identical between humans and chickens
MreB
- prokaryotes
- cell shape
- <15% sequence identity with actin
ParM
- Prokaryotes
- DNA partitioning
- <12% sequence identity with actin and 11% with MreB
ParM and MreB are
actin like protein filaments
functions of actin-like proteins in prokaryotes
1) organelle assembly
- plasmid segregation
- cell shape
MamK
is an actin like protein which forms filaments and organises the magentosome chain
how do we know MamK organises the magentosome chain
using GFP-the wild type shows an ordered chain, whereas mutated MamK shows disordered magentosomes
MreB and Mdl1 are involved in
bacterial morphogenesis
e.g. the cocci shape is lost if either no MreB or no MbI
FtsZ is a
distant prokaryotic tubular homologue.
common features of FtsZ and tubulin
- GTPase activity that controls polymerisation
- formation of protofilaments
- simlar fold
FtsZ forms
in vitro-cell free and in vivo -in cell
where does FtsZ form
a ring at the cell cleavage site- functions in cytokinesis in prokaryotes
ParM filaments are
dynamic
what makes ParM filaments dynamic
polymerisation of ATP bound ParM at both ends. ATP hydrolysis occurs spontaneously
when is the ParM filaments unstable
when ParM-ADP is at an end
ParM filaments function in
plasmid segregation
process of plasmid segregation
1) ParR binds to the centromeric DNA sequence (ParC)
2) ParM polymerises and binds to ParR
3) filament elongation separates the plasmid
- replisome involved
random brownian motion is not sufficient to move
prokaryotic cells around
-bacteria and archaea actively moe through liquids or over most surfaces
models of prokaryotic motility include
swimming, swarming, gliding, twitching
swimming behaviour of bacteria
prokaryotes are too small to sense a nutrient gradient along their cell, they need to swim to find their food
flagella-based motility involves
swimming and swarming
swarming occurs
on surfaces
swimming
- bacteria swim at a rate of 25-160 micrometers per second
- several flagella cooperate in propelling the cell forward
what is used to rotate the flagellum
a basal “motor” that uses a proton gradient to rate the flagellum
what doe she basal motor use to rotate the flagellum
a proton gradient
how many rotations per s in a flagellum
100-300
F0F1-ATPase
found in eukaryotic mitochondria- also a rotation motor- induced by a proton gradient producing ATP
what is secretion based motility
where the action of secretion propels the bacteria along
secretion based motility
- surface-attached motility at around 2-5 micrometers per sec
- some cells rate over secreted adhesion proteins in flavobacterium spp
pili-based motility
twitching
- 100-1000 per cell, 1-2 micrometers long and 2-6 nm wide.
- pili are dynamic and can retract and grow
- pili function in DNA exchange between cells and surface adhesion
what do pili do to cause movement
they change in length and this can be used for gliding over surfaces
twitching motility in pili is used to
form colonies
structure of a pilus
thin polymers made of one protein- Pilin
which proton is used in the formation of pili
Pilin
how do bacteria force the host cell to take them up
many bacteria inject proteins into the human host cell to manipulate the actin cytoskeleton, thereby forcing uptake
how many different secretion systems known
6
type 3 secretion system
injects proteins
-the needle-like structure is used as a sensory probe to detect the presence of eukaryotic organisms and secrete proteins that help the bacteria infect them. The secreted effector proteins are secreted directly from the bacterial cell into the eukaryotic (host) cell, where they exert a number of effects that help the pathogen to survive and to escape an immune response.
types 6 secretion system
injects proteins
is molecular machine used by a wide range of Gram-negative bacterial species to transport proteins from the interior (cytoplasm or cytosol) of a bacterial cell across the cellular envelope into an adjacent target cell. The T6SS was first identified in 2006 in Vibrio cholerae, which causes cholera.
how many proteins injected in the type 3/6 secretory system
15-30
which bacteria have complex protein translocation machines?
gram negative bacteria e.g. Shigella spec. and Yersinia enterocolitica
there are similarities between the
rotation motor of the flagellum and type 3 secretion system
TTSS
type three secretory system
what occurs when bacteria inject components into host cells>
the components interfere with cellular processes and suppress host defences
process of bacterial cell injecting components and interfering with cellular processes
1) secretion system attaches to hot cell
2) needle and translocon attaches to the host cell
3) components from the bacterial cell pass through the basal body and needle into the host cell
4) damaging the cytoskeleton, cell cycle, apoptosis, transcription and
engulfed bacteria escape the vacuole, multiply and start intracellular movement
to avoid attack of the host cell
why do bacteria continuously move around inside cells
impossible to form outer phagosome around the bacteria and therefore cannot be killed
what causes acute inflammation
the bacteria infect the epithelial lying of the colon, causing acute inflammation by entering the host cell cytoplasm and spreading
bacteria… into the neighbouring cell
rocket themselves
what moves the bacteria inside the host cell
actin–> during movement bacteria form cytoskeleton tails at the rear
–> E microscopy indicates the tails consists of actin
what sort of actin is added to the tail to allow movement
G actin
proof that G actin is added to the tails
• G actin (fluorescentand not polymerized) added to bacteria and if the tail is actin, then the bacteria will start moving
what triggers Actin polymerisation
Listeria ActA resembles a host protein and triggers actin polymerisation
how do bacterium make an actin “comet tail”
uses endogenous machinery
how can we prove ActA mediates motility
add it to bacteria and they should start moving
what shoots the bacteria through the cell and across another cell mem.
polar polymerisation
life cycle of a cytosolic bacterium
engulfment, proliferation and motility, which involves being shot into a neighbouring cell
MamK
organelle assembly
ParmM
plasmid segregation
MreB
cell shape
three actin like proteins that make up the cytoskeleton of prokaryotes
MamK, ParM, MreB
MreB and Mdl1 involved in
bacterial morphogenesis
FtsZ
a distant prokaryotic tubular homologue
which protein helps with cytokinesis
FtsZ
