sporulation Flashcards
what is a diaspore
a type of spore found in some bacteria as well as plans and fungi. it has a dispersal mechanism after sexual reproduction
what is an endospore
a type of spore in bacteria which is metabolically inert and is designed to survive harsh conditions and periods of starvation
why is sporulation a last resort
is it energetically costly, takes a long time and is irreversible. it only occurs if stationary phase is not enough to enable survival
what is the transition phase
bacteria has entered stationary phase but has not yet committed to sporulation
which three transcription factors are responsible for controlling sporulation
AbrB, CodY and SpoOA.
what is the role of AbrB
it represses stationary phase genes during exponential phase
what does CodY do
it represses early- stationary and sporulation genes. it is only active when bound by GTP so is indicative of nutrient levels
what does SpoOA do
it is the master regulator or sporulation. at low SpoOAP (monomer) it represses transcription but at high SpoOAP (dimer) it activates transcription of sporulation genes. it regulates 121 genes
how is SpoOA phosphorylated
by a relay of Pi via 5 sensor kinases (Kin A-E), SpoOF, SpoOB, then the D region of SpoOA. the steps allow greater levels of control and sporolation will only occur when there is a threshold amount of SpoOAP dimer present
what upregulates and downregulates phosphorylation of SpoOA
it is upregulated by KipA and downregulated by sda
what unregulated and downregulates transcription of SpoOA
it is promoted by sigma H and is repressed by CodY
what is the role of RAP phosphatase
it removes Pi from SpoOF-P, preventing the formation of SpoOA-P. this is done at a high concentration of bacterial cells which is detected by the movement of small peptides in and out of cells
what is the role of SpoOE
it encodes a phosphatase which dephosphorylates SpoOA-P. this is done at a low, constant rate to prevent accidental build up and premature sporulation
how does the FtsZ ring cause cell division in normal vegetative division
it is positioned in the centre of the cell by proteins DivIVA and MincD. it forms a septum to split the cell into two discrete cells
how does the FtsZ ring cause asymmetrical cell division
more FtsZ is produced so it coils. this coil splits and forms two rings- one at each pole. one of these forms a septum to divide the cell, assisted by SpoIIE phosphatase
what is the role of sda in asymmetrical cell division
it senses whether DNA replication is incomplete. if so, it inhibits phosphorypation of KinA and therefore prevents sporulation
what is the role of SirA in asymmetrical cell division
is displaces DNAA from the OriC (if located there it will initiate replication). this prevents replication being initiated again within the prespore
what promotes transcription of SirA
SpoOA-P
how do chromosomes enter the presopore
they are stretched into a filament due to attraction of SopOJ (bound close to OriC) to DivIVA (located at the poles). only 1/3 is trapped in the prespore at the initial division
how is the whole chromosome moved into the prespore
DNA translocase SpoIIE forms a two channel pore. the two arms of the chromosome are pumped in simultaneously
which sigma factors are active at asymmetrical division
sigma E in the mother and sigma F in the prespore
which sigma factors are active at engulfment
sigma K in the mother and sigma G in the prespore
how sis activation of sigma F controlled
it is inactive when bound by anti sigma factor SpoIIAB. it is active when bound by anti anti sigma factor SpoIIAA
when is SpoIIAA active and inactive
it is inactivated when phosporylated by SpoIIAB (also a kinase). it is active when dephosphorylated by SpoIIE (located in the Z ring)
why is SpoIIAA only active in the prespore, not the mother
there is the same exposure to the Z ring but a much smaller volume. the SA to volume ratio is greater
why can’t SpoIIAA and SpoIIAB both bind to sigma F
steric displacement. they bind to the same region so the binding or one will displace the other
how is sigma E synthesised and activated
it is synthesis as pro sigma E. the inhibiting protein domain is cleaved by GA protease once it has located in the septum and been activated by the binding of SppoIIR on the presopre side
how is sigma G synthesised and activated
it is synthesised inactive due to being bound by SpoIIAB. this is cleaved by SpoIIIJ (produced in the mother) which localises in the septum, cleaved SpoIIAB and activates sigma G
how is sigma K synthesised and activated
to be synthesised the Skin region which divides the gene has to be removed by a SpoIVCA site specific recombinase to produce pro sigma K. this is activated by SpoIVB protease (mediated by sigma G in prespore) cleaving SpoIVFA and BofA protein off pro sigma K, activating it
how is the prespore dehydrated
low weight proteins eg dipicolonic acid enter the prespore along with Ca2+ which causes water to move out of the cell
