AMB16 Flashcards
(18 cards)
how are bacterial genes often arranged
frequently arranged in operons under coordinate genes expressed as single mrna containing multiple ORFs
what is attenutation
common method of bacterial operon reg based on ability of rna transcripts to fold into terminator structures as transcription ad translation occur at the same time
describe the reg of the tryp operon
repression: repressor + tryp bind to operator and prevent transcription
attenuation: based on tRNAtrp conc
- leader transcript that codes for elader peptide contain 2 diff trp codons, if ribosome attempts to translated in low tRNAtrp con it will stall, thus physically shielding seq from forming 1-2 loop so 2 is free to form 2-3 loop which prevents formation of 3-4 termination hairpin which would stop transcription
what are riboswitches
rnas that directly bind to ligands that affect their expression - ligand dependent switch
describe the glmS riboswitch
rna strcuture that is both a ribozyme and riboswitch
enzyme catalyses prod of GlcN6P Glucosamine -6-phospahte
part of glmS transcrip in 5’ UTR is an RNA seq that folds into an endonuclease (ribozyme)
glmS ribozyme is dep on GlcN6P to acheive catalysis of its own cleavage which leads to degredation of mRNA that contains the ribozyme as translation not req when GlcN6P levels are high
what is GlcN6p to glmS ribozyme
a cofactor, as directly participates as an acid base catalyst
what is an aptamer region
part of RNA which can fold to bind ligand
give an example of a riboswitch and describe
ttp riboswitch: tpp binds to aptamer region causing expression platform to form a hair pin loop that blocks RBS
in absense of TPP alternative hairpin forms revealing RBS and gene is switched on.
what is SELEX
systematic evoltuion of ligands by exponential enrichment - tech used in molecular bio for producing oligonts of either ssDNA or RNA that specifically bind to target ligand/ligands
describe SELEX
large library of oligonts synthesised made of randomly generated seqs of fixed length which are then exposed to target ligand - those that dont bind are removed by affinity chromatography and those that bind are amplified by RT-PCR and then repeat binding and select tightly bound rna molecules
after tightly bound molecules found make a gene construct corresponding to seq that can be put into RNA expresssion vector with reporter gfp gene.
= ligand inducible gene expression
artifical riboswitch
give an example of an artificial riboswitch
Neomycin - absense of Neomycin forms a hair pin loop allowing translation of mRNA involved in protein synthesis in gram neg bacteria. - presence of neomycin a different structure forms that stops ability of ribosome to get through, this structure is more stable as more double bonds/no loop = harder to break.
what are small RNAs in bacteria
80-110nt long rnas which are non coding and mostly unknown function, roughly 100 in ecoli genome
what do known sRNAs do?
many act as intermolecular RNA regulators by binding target mRNA and influencing their expression, binding aided byb protein based chaperon Hfq
What do sRNAs DsrA and RprA do?
activate the rpos RNA
what does Oxys sRNA do
represses rpoS by binding to 5’ end including rbs
- produced in response to oxidative stress
what is rpoS gene
gene that encodes an alternative sigma factor S which activates in a stress response
staravation - stationary phase sigma factor
why is it important that oxys inhibits production of sigma factor s
ensures that sppecific response to oxidative stress doesnt trigger the repsonse that is appropriate for other stress conditions
how do DsrA and RprA activate rpoS
by binding to 5’ of mrna which forms a hairpin loop covering rbs, by binding to 5’ end it reaveals rbs allowing ribosome binding.
