eukaryote trans 1 Flashcards
(74 cards)
who proposed the operon hypothesis?
francois jacob and jacque monod
what are the two classes of genes in an operon?
structural (encoded metabolically related enzymes)
regulatory elements( controlled expression of the structural genes)
Mutations in operon structural genes…
abolished one particular enzymatic activity
mutations in operon regulatory genes…
affected all of the different enzymes under its control
is the lac operon what is the function of lacZ?
b-galactosidase activity, metabolizes lactose
is the lac operon what is the function of lacY?
permease, transports lactose into the cells
what happens is LacZ or Lac Y is mutated?
Lactose transport can still be induced in lacZ mutants, and lacY mutants still display lactose-inducible b-galactosidase activity
what happens if the regulatory region of lac operon is mutated?
no lactose transport and no lactose metabolism
what is the function of lacA?
transacetylase enzymes, transfer an acetyl group from acetyl-CoA to galactosides, lactosides, and glucosides.
what is lacI is mutated?
lacI is the repressor, so you will always have some level of LacZ,Y,A expression
what is LacO function?
the site where lacI (the repressor) binds to repress expression of lac operon
what happens in LacO is mutated?
same as what happens in LacI mutant, expression would be constutive of lac operon
how to distinguish between lacI and lacO mutations?
use meridiploids to add second WT copy of lac operon to e.coli
if LacI isn’t functional in one copy the WT will still make LacI and it’ll bind lacO and repress lac operon transcription (“recessive mutation”)
if LacO isn’t functional in one copy the WT will still be bound by the repressor, but the mutant won’t be bound by the repressor. The mutant would still transcribe lac operon genes (“dominant mutation”)
what is a meridiploid?
e.coli are haploid, but you can add a second copy of a gene introduced into genome or plasmid
define a “cis-dominant” mutation
a mutation which only affects the mutant operon but doesn’t affect the WT operon
define a “trans-dominant” mutation
a mutation which only affects the WT operon but doesn’t affect the mutant operon
what happens if LacI^d is mutated in a meridiploid?
dominant negative repressor protein is produced, lac operon constitutively expressed. a repressor that can no longer bind operator (lacO) is produced, the repressor protein is a tetramer so only one copy being mutated will result in a dysfunctional repressor protein
how many subunits is the lac repressor protein?
tetramer
what happens if LacI^s is mutated in a meridiploid?
this mutant is “unresponsive to the inducer”, cis- and trans dominant
difference between lacI^d and lacI^s mutants?
the s mutant binds the lacO site but is dysfunctional so transcription of lacOperon is not repressed, the d mutant cannot bind the lacO site at all so transcription is not repressed
difference bt prokaryote and eukaryote transcription factor binding?
prokaryotes if the TF is made it will always have access to DNA, in eukaryotes other factors can prevent TF from binding DNA
define nonrestrictive transcription
in prokaryotes TF can always bind DNA
define restrictive transcription
in eukaryotes other factors may need to be present for TF to bind DNA
major difference bt accessing DNA in pro and eukaryotes?
nucleosomes (histones) aren’t present in prokaryotes
