L8: Regulation of Prokaryotic Transcription Flashcards
Genes are often organized as _____
operons
Prokaryotic genes are _____–one promoter direct the synthesis of a mRNA that can encode more than one proteins
polycistronicc
Polycistronic
One promoter direct the synthesis of mRNA that can encode more than one proteins
Operon
An arrangement of genes in a contiguous linear array
An arrangement of genes in a contiguous linear array
Operon
In an _____ a continuous strand of mRNA carries the message for a related series of enzymes (polycristonic mRNA)
operon
Why are genes organized into operons?
- genes encoding enzymes in a common pathway can all be induced simultaneously
- known as “coordinate control”
- one mRNA expresses multiple proteins
Coordinate control
- type of control where genes encoding enzymes in a common pathway can all be induced simultaneously
- one mRNA expresses multiple proteins
- type of control where genes encoding enzymes in a common pathway can all be induced simultaneously
- one mRNA expresses multiple proteins
coordinate control
Transcription of the structural genes is controlled by _____ protein
repressor
_____ sequence determines first level of regulation
Promoter
Promoter sequence determines first level of regulation
- weak promoters have poor consensus sequences and initiate transcription infrequently
- strong promoters generally have good consensus sequences and initiate transcription often
- many promoters are regulated by addition regulatory proteins as well
- repressors inhibit transcription initiations (Lac repressor)
- activators increase transcription initiation (CAP)
_____ promoters have poor consensus sequences and initiate transcription infrequently
weak
_____ promoters generally have good consensus sequences and initiate transcription often
strong
weak promoters have _____ consensus sequence and initiate transcription _____
poor
infrequently
strong promoters generally have _____ consensus sequences and initiate transcription _____
good
often
Repressors
- inhibit transcription initiation
- block transcription initiation
- ex: lac repressor
Activators
- increase transcription initiation
- speeds up transcription
- ex: CAP
_____ inhibit transcription initiation
repressors
_____ increase transcription initiation
activators
An example of repressor
Lac operon
An example of activator
CAP
3 levels of transcription
- basal level
- repressed
- activated
_____ _____ proteins can facilitate these distal interactions
DNA bending
Repressors usually block transcription initiation by:
- interfering with RNA polymerase binding
- preventing open complex formation
Lac operon consist of _____ genes under the control of a single operator
3
3 genes of lac operon
- lacZ
- encodes beta-galactosidase, an enzyme tha tcatalyzes the hydrolysis of lactose
- lacY
- encodes the lactose permease, required for transport of lactose into the cell
- lacA
- encodes a transacetylase enzyme that transfers an acetyl group from acetyl-CoA to Beta-galactosides
- the cell can use lactose as an energy source by producing the enzyme beta-galactosidase to digest lactose into glucose and galactose
- encodes a transacetylase enzyme that transfers an acetyl group from acetyl-CoA to Beta-galactosides
lacZ
- encodes beta- galactosidase
- an enzyme that catalyzes the hydrolysis of lactose
beta-galctosidase
enzyme that catalyses the hydrolysis of lactose
enzyme that catalyzes the hydrolysis of lactose
beta-galactosidase
lacY
- encodes for lactose permease
- required for transport of lactose into the cell
lactose permease
required for transport of lactose into the cell
required for transport of lactose into the cell
lactose permase
lacA
- encodes a transacetylase enzyme
- transfers an acetyl group from acetyl-CoA to Beta-galactosides
transacetylase enyme
transfers an acetyl group from acetyl-CoA to Beta-galactosides
transfers an acetyl group from acetyl-CoA to Beta-galactosides
transacetylase enzyme
encodes for Beta-galactosidase
lacZ
encodes for lactose permease
lacY
encodes for transavetylase enzyme
lacA
Cell can use _____ as an energy source by producing the enzyme beta-galactosidase to digest lactose into glucose and galactose
lactose
Cell can use lactose as an energy source by producing the enzyme beta-galactosidase to digest lactose into _____ and _____
glucose
galactose
High levels of lactose result in _____-_____ production
Beta-Gal
High levels of _____ result in Beta-Gal production
lactose
Hydrolysis to galactose and glucose sugras = _____ in cell
energy
Hydrolysis to _____ and _____ sugars = energy in cell
galactose
glucose
substrate and inducer used in _____ _____ studies
Lac operon
Inducer: IPTG
will induce the lac operon but is not metabolized, so its concentration stays constant during an experiment
_____ will induce the lac operon but is not metabolized, so its concentration stays constant during an experiment
IPTG
Substrate:
Bacterial colonies expressing B-galactosidase turn blue on agar plates containing __-___, which is a substrate for B-galactosidase but is not an inducer
X-gal
X-gal
A substrate for B-galactosidase that makes bacterial colonies expressing B-galactosidase to turn blue on agar plates
lacI
- not part of the lac operon but codes for repressor
- has separate promoter and is transcribed independently of lacZ, lacY, and lacA
_____ is not part of the lac operon but codes for repressor
lacI
Mutations
changes in the normal DNA sequence
_____ are changes in the normal DNA sequence
Mutations
_____ cells have mutations in the normal DNA sequence found in cells isolated from the wild
Mutant
“wild type” sequence
DNA sequence found in cells isolated from natural sources in the wild
____ are DNA sequence found in cells isolated from natural sources in the wild
“wild type” sequence
Inducible synthesis
synthesis that is turned on by an inducer
______ _______ is a synthesis that is turned on by an inducer
inducible synthesis
Constitutive synthesis
- synthesis at a constant level in the presence or absence of inducer
- loses all regulatory control of the lac operon
_____ _____ is a synthesis at a constant level in the presence or absence of inducer
Constitutive synthesis
I- mutants
mutant in I gene, resulting in a defective repressor
O^c mutants
mutant in the binding site (operator) for the repressor
Mutant in I gene, resulting in a defective repressor
I- mutants
Mutant in the binding site (operator) for the repressor
O^c mutants
I- and O^c mutants can be distinguished by analyzing _____ _____
partial diploids
I- and O^c mutants can be distinguished by analyzing partial diploids
- both result in constitutive expression of B-galactosidase
- since bacteria are haploid, a plasmid can be used to introduce a second copy of the lac operon into the cell
- I- and O^c mutations behave differently in the cis vs. trans arrangement
O^c mutation is physically linked to the _____ gene (cis)
Lac Z
_____ _____ is the protein product of the I gene
- it is diffusible within the cell (trans)
Lac I Repressor
Widetype situation
lac operon is transcribed only in the presence of an inducer
Mutation in the lac repressor gene (lacI) results in _____ _____ because no repressor is made
constitutive expression
Mutation in the operator results in _____ _____ because the operator site is lost and repressor can’t bind
constitutive expression
When the repressor is supplied in trans, _____ is observed again
regulation
When operator is supplied in trans, there is _____ ______
no effect
lac operon is also under _____ control
positive
Glucose metabolism is favored over _____ meabolism
lactose
Level of glucose in media is detected by _____
cAMP
high glucose = low cAMP = no CAP (low transcription)
low glucose = high cAMP = bring in CAP (high transcription)
_____ binds to specific DNA sequences
CAP-cAMP
Binding results in a bend in the _____
DNA
_____ also interacts directly with the RNA polymerase to stimulate binding to weak promoter sequences
CAP-cAMP
RNA polymerase binding at _____ _____ with the help of CAP
lac promoter
CAP is recognized by the _____ of polymerase
CTD (carboxyl terminal domain)
CAP is _____ which increases transcription
activator
