Gene Regulation: The Operon Flashcards
the functioning unit of DNA consisting of a cluster of genes under the control of single promoter; several structural genes arranged under a common promoter and regulated by a common operator
operon
T/F the regulators of a given operon are not necessarily coded for by that protein
T
a nucleotide sequence that enables a gene to be transcribed; recognized by RNA polymerase which then initiates transcription
promoter
a segment of DNA to which a repressor binds
operator
the genes that are co-regulated by the operon
structural genes
a constantly expressed gene which encodes for repressor proteins
regulatory gene
proteins that suppress transcription of a gene in response to an external stimulus
repressors
proteins that increase transcription of a gene in response to an external stimulus
activators
(small molecule) can displace a repressor (protein) from the operator site, resulting in activation of operon
inducers
can bind to the repressor to allow its binding to the operator site
corepressor
control of an operon is a type of ____________ that enables organisms to regulate the expression of various genes depending on environmental condition
gene regulation
when an inducer is present, it binds to the repressor and makes it unable to bind to the operator, which allows for expression of the operon
negative inducible operon
What type of operon is the lac operon?
negative inducible operon
what is the inducer molecule in the lac operon?
allolactose
corepressors are bound by the repressor protein which causes a conformational change to the active site so the activated repressor protein binds to the operator and prevents transcription
negative repressible operon
what type of operon is the trp operon
negative repressible operon
activator proteins are normally unable to bind to the DNA; when an inducer is bound by the activator protein, it undergoes a change in conformation so that it can bind to the DNA and activate transcription
positive inducible operon
activator proteins are normally bound to the DNA segment; when an inhibitor (corepressor) is bound by the activator, it is prevented from binding the DNA which stops activation and transcription of the system
positive repressible operon
codes for the enzyme B-galactosidase which breaks B-galactoside into its component sugars
lac Z
codes for the B-galactoside permease, a membrane-bound protein constituent of the transport system
lac Y
codes for B-galactoside transacetylase, an enzyme that transfers an acetyl group from Acetyl-CoA to B-galactosides
lac A
the lac repressor is inactivated by _____________________ where inducer binding changes the properties of the DNA binding site
allosteric interaction
What are the repressor’s two binding sites?
one for the operator DNA and one for the inducer
describe the lac operon mechanism involving glucose.
glucose is a better energy source than lactose so there’s no need to turn the operon on if glucose is available
cAMP-CAP protein complex serves as a ______________ to induce transcription
positive regulator
when does cAMP begin to accumulate in the cell?
when glucose levels drop
signaling molecule that is involved in glucose and energy metabolism in E.coli
cAMP
what happens when cAMP binds to the CAP
the complex binds to the promoter region that switch on the genes for processing of alternative energy source
what is the trp operon?
it has 5 genes that E.coli can use to synthesize tryptophan when it is not available in the environment
What happens to the trp operon when tryptophan is absent?
the repressor can’t bind to the operator so the operon is active and tryptophan is synthesized
