week 3 : transcriptional regulation in prokaryotes Flashcards
why is gene expression regulated
prokaryotes only express genes if and when needed to conserve energy
At what points can gene expression be regulated
1) Hydrolyse mRNA, preventing translation
2) Prevent translation at the ribosome
3) Protein can be degraded after it is made
4) Inhibit the proteins functions
what is a promoter
a sequence of DNA next to the gene where transcription factors bind
where do sigma factors bind to
core promoter elements at -10 and -35 sequences
what do sigma factors recruit
RNA polymerase
core promoter element variants are bound by specific sigma factors, what does this allow for ?
coordinated gene expression
strong promoters have a close match to the consensus sequence what does this result in
tight binding of RNA polymerase and high mRNA production
repressor protein
binds to repressor binding site blocking transcription
activator protein
binds to activator binding site and stimulates gene expression
allosteric regulation of enzymes vs regulation of gene expression
allosteric regulation allows for rapid fine tuning whereas regulating gene expression is slower but conserves resources
inducer
compound that induces protein synthesis
inducible proteins
their synthesis can be induced by an inducer
define operon
cluster of genes with a single promoter that is transcribed together into a single mRNA.
what do operons consist of
a promoter, two or more structural genes and an operator
what conditions are required for the lac operon to be fully expressed
when glucose is absent and lactose is present
