Prokaryotic Gene Structure 4 Flashcards
bacterial gene regulation
what are the two levels of control of bacterial gene expression?
1. @ diff levels of info transfer
* replication
* initiation of transcription
* transcriptional elongation
* post-transcription
* translation
* post-translation
2. global regulatory systems
* affect many genes & pathways at the same time
what are the 3 types of gene expression
and brief description
- constitutive genes (expressed continuously) ON
- inducible genes (specifically activated for expression) OFF
- repressible genes (specifically repressed expression) ON
what are inducible genes?
genes that are off unless an inducer is present to promote gene expression
what are repressible genes?
genes that are on except when an inhibitor/corepressor is present that suppresses gene expression
what are activators & repressors?
regulatory proteins that bind to DNA & whose activity may be modulated by binding of inducers or inhibitors
what do activators do
promote/induce transcription = positive control
what do repressors do
repress/inhibit transcription = negative control
what are small effector proteins/metabolites (3)
+ function
- non-covalently bind regulatory proteins as activators or repressors
- change activity of regulatory proteins
- affect transcription by interacting w regulatory proteins
Inducible genes can be positively controlled and repressible genes can be negatively controlled depending on what ? (4)
- presence of activator & operator sites (cis sites) on DNA associated with specific gene.
- binding of activator and repressor regulatory proteins (inducers and/or inhibitors) on cis sites.
- positive regulatory control mechanisms for inducible genes and repressible genes.
- negative regulatory control mechanisms for inducible genes and repressible genes
what is a cis-regulatory element?
+ examples
region of DNA/RNA involved in regulating expression of genes located on the same molecule
examples for DNA: consensus sequence
RNA: shine dalgarno, rut site
ito of inducible genes, what happens in the absence of an inducer? (positive control)
activator cant bind to activator site & no transcription by RNA polymerase
what does it mean for an inducible gene when an inducer is present? (positive control)
changes conformation of activator protein and allows it to bind to its activator site, which allows RNA polymerase transcription
in the absence of an inducer, what is the difference in what happens to the inducible gene in negative and positive control
positive control = activator can’t bind to activator site & no transcription by RNA pol
negative control = repressor blocks transcription by RNA pol by binding to operator site within promoter region
in the presence of an inducer, what is the difference in what happens to the inducible gene in negative and positive control
positive control = changes conformation of activator protein and allows it to bind to its activator site, which allows RNA polymerase transcription
negative control = changes conformation of repressor protein upon binding to it & releases it from operator site
in the absence of an inhibitor, what is the difference in what happens to the repressible gene in negative and positive control
positive control = activator can bind to activator site & facilitates transcription by RNA pol
negative control = repressor unable to bind to operator site & transcription occurs
in the presence of an inhibitor, what is the difference in what happens to the repressible gene in negative and positive control?
positive control = changes conformation of activator protein so can no longer to its activator site - prevents transcription
negative control = changes conformation of repressor protein upon binding & allows repressor + inhibitor to bind to operator site & no transcription
why is the nucleotide sequence of the promoter (a cis regulatory element) important?
- it determines strength & stability of binding by RNA pol to promoter region (influences efficiency initiation of transcription)
- weak binding by RNA pol due to deviations from consensus sequence = weak transcription
what is an example of trans-regulatory elements?
repressor & activator proteins
what is an example of post-transcriptional regulation and explain how it works?
mRNA stability
mRNA half-life results in short or long translation window for ribosomes (short half life = few proteins produced from mRNA molecules)
what is mRNA half-life?
when mRNA exists for a few seconds to several hours as a result of 3D struc of mRNA
what type of regulation is the shine dalgarno sequence and how does it regulate?
- translational regulation
poor shine delgarno = weak binding of ribosome (little protein produced)
how do sRNAs (non coding RNAs) act as a form of regulation?
- translational regulation
- some sRNAs base pair to leader region of target mRNAs to block ribosome binding (and translation)
- some sRNAs promote translation by binding to mRNA - change secondary structure
what is the general concept of a riboswitch?
small-molecule ligand binds to mRNA molecule to regulate the expression of the mRNA molecule
what is the riboswitch region?
upstream of shine dalgarno in form of a hairpin loop that has binding site for ligand
