Regulation I Flashcards
in the regulation of gene expression in prokaryotes, what is the term for genes that encode proteins?
structural genes
in bacteria, structural genes for proteins with a related function are often grouped sequentially into units called?
operons
what are the two main sequences we are concerned with in an operon?
promoter and structural genes (1-3, that encode for proteins 1-3, each with a start and stop codon)
T/F, The genes in an operon are expressed coordinately (they are either all “turned on” or all “turned off”)
T
when an operon is expressed, all, some or none of the genes are transcribed in a single polycistronic mRNA?
all
what region of the gene regulates the transcription of the genes?
the promoter region
multiple sets of start and stop codons that allow several different proteins to be produced from this single transcript at the translational level is called?
polycistronic mRNA
in the regulation of RNA polymerase, what are repressors?
regulatory proteins that prevent the binding of RNA polymerase to the promoter and thus act on initiation of transcription.
what is a repressor encoded by?
a regulatory gene
once the repressor is produced, what is the region of the promoter called? importance?
operator and blocks binding of RNA polymerase OR inhibits transcription initiation
what are the two regulatory mechanisms responsible for negative control in the gene expression of prokaryotes?
induction and repression
what is an inducer?
A small molecule which stimulates expression of the operon by binding to the repressor and changing its confirmation so that it can no longer bind to the operator
what is repression?
a co-repressor required to activate the repressor
what happens to gene expression in prokaryotes when an inducer is present?
RNA polymerase can bind to the promoter and transcribe the operon
what happens to gene expression in prokaryotes when an inducer is not present?
The repressor is active, transcription is repressed, the genes in the operon are not expressed.
what is responsible for the induction of the lac operon in prokaryotes?
lactose, alpha 1,4 linkage; used in the metabolism of lactose, readily used as allolactose, alpha 1,6 linkage, by the bacteria to produce 3 additional enzymes required for lactose metabolism which are encoded on the lac operon
what are the three enzymes produced from the lac operon in prokaryotes?
B-Galactosidase
Permease
Transacetylase
in prokaryotes, what is B-Galactosidase?
splits lactose
in prokaryotes, what is Permease?
transport of lactose into the cell
in prokaryotes what is Transacetylase?
acetylation of B-galactosides
in prokaryotes, what are the co-repressors?
A small molecule (nutrient or its metabolite) that binds to a repressor changing its status from inactive to active.
what is the effect of the repressor - co-repressor complex binding to the operator in prokaryotes?
it prevents RNA polymerase binding and gene transcription
why is the trp operon important in prokaryotes?
its used to synthesize enzymes
in the regulation of gene expression in prokaryotes, what happens when tryptophan is available?
E. coli cells save energy and no longer make the enzymes
Tryptophan is a co-repressor that binds to the inactive repressor, causing it to change its confirmation and bind to the operator, thereby inhibiting transcription.
what is the difference between Trp and Lac operon?
trp inactivates the operon and production of enzymes, for lac, lactose has to be available to make the necessary enzymes
in the regulation of gene expression in prokaryotes, what happens to cAMP levels when glucose levels are low.
increase cAMP, and vice versa. When glucose is is high, cAMP is low
what does cAMP do to the RNA polymerase if it becomes synthesized?
so glucose levels are low, allolactose is elevated, and so cAMP is elevated to act as an inducer to continue synthesis of the enzymes by allowing the binding of the RNA polymerase
how can the transcription of the lac operon be induced?
by allolactose if glucose is absent. The enzymes encoded by thelacoperon are not produced if cells have an adequate supply of glucose, even if lactose is present at very high levels.
how many polymerases does E. Coli have?
1 RNA polymerase
what is the importance of the sigma factors binding to the RNA polymerase? name the standard sigma factor?
stimulating its binding and activating transcription; σ70
other sigma factors are involved in the regulation of gene expression in prokaryotes? whats the purpose? result?
sigma 32; Helps RNA polymerase recognize promoters for the different operons that encode heat-shock proteins.
Result: Increased transcription of genes for heat-shock proteins which prevent protein denaturation at high temperature
Occurs in response to elevated temperatures.
what is attenuation?
A regulatory feature found in bacteria that causes premature termination of transcription.
Involves a provisional stop signal (attenuator), located in the DNA segment that corresponds to the leader sequence of mRNA
what is the effect of the ribosomes in the attenuator region in the mRNA leader in prokaryotes?
they become stalled and depending on metabolic conditions, the attenuator either stops the transcription or allows it to continue
where does transcriptional attenuation occur only?
in prokaryotes because translation of an mRNA begins before its synthesis is complete.
why does attenuation not occur in eukaryotes?
because the presence of a membrane-bound nucleus spatially and temporally separates transcription and translation.
where is the leader sequence located?
a region on the mRNA that is directly upstream of the initiation codon
in the attenuation of transcription in prokaryotes, what happens when Trp levels are high?
High levels of Trp-tRNATrp allow for the complete leader peptide to be made
Regions 3 and 4 form a transcriptional termination signal
in the attenuation of transcription in prokaryotes, what happens when Trp levels are low?
Ribosome stalls at adjacent Trp codons in region 1 because of low levels of Trp-tRNATrp
Regions 2 and 3 form a different hairpin structure that does not signal termination of transcription, RNA pol continues
T/F, attentuation is the second mechanism of feedback in the trp operon?
T
if the TrpR repressor decreases transcription by a factor of 70, how much more can attenuation decrease it?
by a factor of 10 thus allowing accumulated repression of about 700-fold
