Transcriptional regulation in prokaryotes Flashcards
How are “housekeeping genes” expressed
constitutively
What type of gene expression is “switched on and off”
induced or repressed
What processes are controlled by housekeeping genes
metabolism
In prokaryotes, at what level does most transcription occur and why
transcription i.e. before the synthesis of mRNA
to conserve energy and resources
What is a promoter
the sequence of DNA adjacent to the gene which determines where and in which direction RNA polymerase binds DNA
Explain positive regulation
The gene is on unless the protein is present
Explain negative regulation
The gene is off unless the protein stimulates transcription
What do sigma factors do and where do they bind
A transcription factor which recruits RNA polymerase binds core promoter elements (-10 and -35 sequences)
What dictates the rate of transcription of sigma factor-induced transcription
The variance of the signal sequences they bind
Strong promoters conform well to the consensus sequence and frequently initiate transcription
Explain coordinated gene expression in prokaryotes
variants of sigma factors can bind multiple genes in response to the same stimuli
Which saccharide is preferred for ATP synthesis
glucose
When conditions dictate how is lactose used for ATP synthesis
split into two galactose and acetylated to metabolise it
takes 3 enzymes
What is an inducer
a compound that induces protein synthesis making inducible proteins
What are constitutive proteins
proteins made at a constant rate
Explain the two methods of regulation of metabolic pathways
allosteric regulation of enzyme-catalyzed reactions - faster fine-tuning, higher energy requirements
regulation of gene expression (of enzymes) - slower with a lag time but conserves resources
What is an operon
a cluster of genes with a single promoter that is transcribed together into a single mRNA, usually involved in the same processes
What does an operon consist of
a promoter
two or more structural genes
an operator
what is an operator
a short stretch of DNA between the promoter and structural genes of an operon that allows for regulatory protein binding
Explain the three ways to control operon transcription
inducible operons - regulated by a repressor, default is off, turned on by a metabolic substrate eg lactose
repressible operons - regulated by a repressor, default is on, repressed when a corepressor binds its repressor
regulated by activator protein - default is off unless stimulated
where is the repressor for the lac operon encoded and how is it transcribed
before the promoter
constitutively
What is the role of lactose in the lac operon system
inducer
it changes the conformation of the repressor so it cannot bind DNA
What is polycistronic mRNA
mRNA that encodes multiple proteins
What type of pathway do inducible systems control and when are they turned on
catabolic
when substrate is available
What type of pathway do repressible systems control and when are they turned on
anabolic pathways
on until product concentration becomes excessive
What is CRP and what happens when it is bound
cAMP receptor protein
binds the promoter region and makes sigma factor/RNA polymerase binding more efficient
When is CRP activity highest
when cAMP levels are low due to glucose and lactose being at high levels
