Prokaryotic Gene Regulation Flashcards
What is the central dogma and define gene regulation
TRANSCRIPTION TRANSLATION
DNA –> RNA ———-> PROTEIN
Genes are regulated by DNA binding proteins.
How does transcription in prokaryotes work and how is it different to eukaryotes
- DNA copied by DNA-dependent RNA pol to produce mRNA
- RNA pol binds to promoter region and initiates polymerisation of mRNA strand
- amount of mRNA produced depends on frequency of RNA pol attachment
Different to eukaryotes as there is no nuclear membrane separating transcription from translation (more efficient)
How does translation in prokaryotes work and how is it different to eukaryotes ?
- Ribosome binds to a specific substance on the mRNA with an initiation tRNA
- Start codon initiates translation and moves along the mrRNA
- Chain terminated happens at one of the three stop codons
Similar to eukaryotes, no nuclear membrane so translation can proceed on the 5’ end of the new and emerging mRNA (more rapid response)
How does translation in prokaryotes inhibit bacterial growth (can exploit with antimicrobials)
Bacteria use 70s ribosomal complex instead which is different from the eukaryotic 80s - target for aminoglycosides
What is an operon?
Several genes are regulated by one promoter (unit of DNA )
-efficient packaging of genes on chromosome
What is a regulon?
Sets of operons that are controlled by one regulator protein
- Synchronises large and complex processes
- Cap regulator controls over 100 genes in E.Coli
What are DNA binding proteins?
Regulate gene expression by altering access of RNA polymerase to the promotor site: activation, repression
Trans acting factors - DNA binding proteins (BP)
- BPs bind to DNA sequences (promotor, operator), these segments are known as cis-acting elements –> regulate genes which they are located next to
What is lac operon and how does it work in absence of glucose or lactose
An example of inducible operon
- transcribed and polycistronic mRNA
- Regulator is CAP
- For CAP to bind to the operator, the cell needs cAMP
cAMP levels are low when glucose is available
(A) when glucose is absent and lactose is present –> CAP + cAMP bind to operator –> RNA pol –> mRNA
(B) when glucose available, there is low cAMP and CAP cannot bind to the operator –> RNA pol cannot bind –> no mRNA
(C) in absence of lactose, LacI repressor protein binds to the operator and inhibits RNA poly causing transcription.
> When lactose is present, LacI protein is inhibited by an inducer protein (allolcatose)
(D) No lactose or glucose: no glucose = high levels of cAMP so will attach to cap and activate Lac operon but there is no lactose so there is an additional regulatory element o make sure when there is no glucose and cAMP levels are high, it still shut down in absence of glucose
How is Diphtheria and Pertussis toxins regulated in terms of their virulence factors
Diphtheria: Negative regulation by suppressor protein DtxR if Fe present
- When Fe present, Fe binds to DtxR –> bind to operator and inhibits toxin production
Pertussis (two component system):
Doesn’t express virulence factors unless it has right env
- Sensor protein (BvgS)
> activated by auto phosphorylation
-BvgA binds to operator of many genes (regulon)
–> pertussis toxin operon and other virulence associated genes –> gene regulation
How is P. aeruginosa regulated in terms of their virulence factors
Qurom sensing: mechanism by which certain genes are activated when a particular bacteria density is achieved
- Biofilm is produced p. aeruginosa during lung infections in cystic fibrosis patients
> Biofilm protect bacteria from immune system and chemicals –> difficult to reat
- When p.aerugionsa reach a certain desnity, signalling compounds released into surroundings reach a certain threshold conc
- receptors are then activated and results in activation of genes to produce a biofilm.
