osmolarity

Question 1

where does autophosphorylation occur

Answer 1

in the catalytic domain of the dimerised sensor kinase. it is then moved to the histidine kinase domain

Question 2

does the catalytic domain give the Pi to the histidine kinase domain of the same monomer

Answer 2

sometimes- this is called cis. if it gives it the the other monomer of the dimer it is trans

Question 3

when do response regulators dimerase

Answer 3

only after the response regulators have been phosphorylated can they be dimerised to bind to both DNA promoters and RNAP

Question 4

how is phosphotransfer more easily seen

Answer 4

using BeF3 instead of PO4- it mimics its function but is more visible

Question 5

what is the fingerprint

Answer 5

amino acids surrounding H and D of SK and RR respectively which interact with each other to bring the two components together

Question 6

what is second site suppression

Answer 6

mutations in the fingerprint can stop the two components being brought together and prevent transcription. if the bacteria are left to reproduce and mutate they can compensate for the mutations and restore transcriptional function

Question 7

what is pathway insulation

Answer 7

a two- component regulator existed but id replicated. one of the copies retained function whilst the other evolved. eventually they became insulated from each other with two distinct functions

Question 8

what is osmolarity

Answer 8

a measure of the levels of dissolved substances in a solution

Question 9

how does EnvZ- OmpR respond to osmolarity

Answer 9

it regulated the expression of two outer- membrane poring OmpC and OmpF

Question 10

how do OmpR-P levels reflect osmolarity

Answer 10

when osmolarity is low there is little OmpR-P, when osmolarity is high there is more

Question 11

how are ompF and ompC different

Answer 11

ompF had a diameter of 1.16nm, ompC has one of 1.08nm

Question 12

which porins are expressed at high osmolarity

Answer 12

this is usually in the gut. ompC is expressed to maximise food intake. ompF is not expressed to prevent intake of bile salts which would damage the bacteria

Question 13

which porins are expressed at low osmolarity

Answer 13

this is usually in open water. ompF is expressed to maximise food intake. ompC is not expressed as it would be wasteful to express it as well as ompF

Question 14

how is water intake involved

Answer 14

in low osmolarity water briefly enters and the cell swells. in high osmolarity water briefly exits, ions enter and the cell shrinks. these changes cause the bacteria to respond to the osmolarity changes quickly to prevent damage

Question 15

what does OmpR-P bind at high osmolarity

Answer 15

in binds to low affinity boxes- the C box in ompC activated transcription, and the C/Fe/Fd boxes in ompF which causes the promoter to loop (with the help of IHF) and inhibits transcription

Question 16

what does OmpR-P bind at low osmolarity

Answer 16

high affinity boxes- FabC box in ompF which activated transcription. it cannot bind to any regions in the ompC promoter so there is no transcription

Question 17

which amino acids are involved in bonding of the RNAP and the regulator domain

Answer 17

V264, D280 and Q283 in the alpha C terminal of the RNAP interact with P179, S181 and R182 in the regulator domain. there is evidence of second site suppression here

Question 18

what else does OmpR-P regulate the expression of

Answer 18

it regulates the expression of omrA and B which prevent the translation of ompT mRNA

Question 19

what is the role of OmpR-P in disease

Answer 19

it is essential is infections of the urinary tract- without in the mutants couldn’t respond to changes in osmolarity in the urine

Question 20

how does EnvZ change

Answer 20

the histidine kinase domain changes in response to osmolarity- the loop is longer in low osmolarity and shorter in high osmolarity

Question 21

what is the role of procaine

Answer 21

it is an external factor which can alter EnvZ by artificially changing the shape of the sensor