OPERONS: FINE CONTROL OF BACTERIAL TRANSCRIPT Flashcards
__________ - first operon discovered which became the prime example
for operon concept
Lac Operon
contains three (3) coding genes for E. coli protein to permit to use
the sugar lactose
- _____________ - transports the lactose into cells
- _______________ - cuts lactose into galactose and glucose
- ________________ - unclear function in lactose
metabolism
Galactoside permease (lacY)
B - galactosidase (lacZ)
Galactoside transacetylase (lacA)
they are transcribed to produce one messenger RNA known as
____________ - comes from a single promoter.
each ________ in the mRNA has its own ribosome binding site so each cistron – can be translated by separate ribosomes that bind independently of each other.
polycistronic message ; cistron
E. coli cells growing on a medium containing sugars _____ and _____ – cells exhaust the glucose and stop growing
glucose and lactose
o _______ resumes - after an hour
o ______ - cells have been turning on the lac operon and beginning to accumulate the enzymes they need to metabolize lactose
* _______ - latin word auxilium meaning help
* Bacteria need an enzyme to transport the lactose into the cells named _____________
o Cells - need an enzyme to break the lactose down into 2 component sugars: _________ & ________
growth ; During lag ; Diauxic ; Galactoside permease ; Galactose & glucose
(CONTROL OF LAC OPERON)
- like “brake” of car; needed to
released to be able to move - ________ - a protein called as lac
repressor which keeps the
operon turned off as long as
lactose is absent
Negative Control ; Brake
(CONTROL OF LAC OPERON)
like accelerator pedal
- ________ - additional postive
factor; responds to low glucose
levels by stimulating transcription of
the lac operon - ______ - keep the
concentration of the activator low,
so transcription of the operon
cannot be stimulated - Advantage: keeps the operon
neearly turned off when level of
glucose is high
Positive Control ; Activator ; High glucose levels
(NEGATIVE CONTROL OF LAC OPERON)
implies that operon is turned on unless lac repressor intervenes to stop it.
Negative control
(NEGATIVE CONTROL OF LAC OPERON)
_____________ - lac repressor; turns off the lac operon
o When the repressor binds to the operator or as long as there’s no lactose available, the operon is __________
o Repressor bound to operator – prevents ____________ from binding to the promoter and transcribing the operon
Off regulation ; repressed ; RNA polymerase
(NEGATIVE CONTROL OF LAC OPERON)
_______ - product of a regulatory gene
- tetramer of 4 identical polypeptide; binds to the operator on the right of promoter
lacl gene
(NEGATIVE CONTROL OF LAC OPERON)
___________ - an repressor; binds to one molecule to the protein changes the shape of a remote site on
the protein and alters its interaction with a second molecule
Allosteric protein
(NEGATIVE CONTROL OF LAC OPERON)
Greek: ____ = other + ______ = shape
allos ; stereos
(NEGATIVE CONTROL OF LAC OPERON)
_______ - first molecule; binds to the repressor causing protein to change to a conformation that favors
dissociation from operator
- an ____________; alternative form of lactose
Inducer ; Allolactose
(NEGATIVE CONTROL OF LAC OPERON)
NATURE OF INDUCER
* Inducer of ________ - binds the repressor
* Inducer of ________ - Alternative form of lactose
* When ____________ cleaves lactose to galactose plus glucose, it rearranges a
small fraction of the lactose to allolactose
lac operon ; Allolactose ; Beta - galactosidase
(DISCOVERY OF THE OPERON)
- 1940s-1950s; studies the metabolism of lactose by E. coli
- 3 enzyme activities or genes were induced together by galactosides
- __________ - needed no induction, genes are active all the time
FRANCOIS JACOB AND JACQUES MONOD ; Constitutive mutants
(DISCOVERY OF THE OPERON)
studying the inducibility of lactose metabolism in E. coli
MONOD, 1940
(DISCOVERY OF THE OPERON)
important feature of lactose metabolism
BETA-GALACTOSIDASE
(DISCOVERY OF THE OPERON)
used an anti-beta-galactosidase antibody to detect beta-galactosidase protein
MONOD & MELVIN COHN
(DISCOVERY OF THE OPERON)
- found that could make beta-galactosidase but still could not grow on lactose
- ____________ = added radioactive galactoside to wild type and mutant bacteria
- ___________ - did accumulate the galactoside
Monod & co-workers ; Wild type cells
(DISCOVERY OF THE OPERON)
created merodiploids or partial diploid bacteria which carries the both wild type (inducible) and constitutive alleles
ARTHUR PARDEE, JACOB AND MONOD
(DISCOVERY OF THE OPERON)
__________ produces a repressor protein that can diffuse throughout the nucleus
__________ = bind to both operators in ameriploid as it can act on loci on both DNA molecules (Latin: trans = across)
_______ - controls only the operon on the same DNA (known as cis-acting gene)
REPRESSOR GENE ; Trans-acting ; Operator
(REPRESSOR-OPERON INTERACTION)
______________ - succeeded in partially purifying the lac repressor; used a mutant e. coli strain with a repressor mutation (lact) which cause the repressor to bind IPTG (isopropylthiogalactoside)
Walter Gilbert and Benno Muller-Hill
(REPRESSOR-OPERON INTERACTION)
___________ - used repressor purified or nitrocellulose filter-binding assay and demonstrated that lac repressor binds to lac operator.
showed DNA containing the constitutive mutant operator ________ required a higher concentration of repressor to achieve full binding than did the wild-type operator.
Melvin Cohn and his colleagues ; (lacO^c)
(REPRESSOR-OPERON INTERACTION)
This experiment showed that a genetically defined constitutive lac operator has ______ than normal affinity for the lac repressor, demonstrating that the sites defined genetically and biochemically as the operator are one and the same.
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