lecture 18 Flashcards
(25 cards)
bacteria that undergo ____ transcription have no ___ genes
constitutive transcription
regulatory genes
regulation of bacterial genes is the predominant mode that takes place in what 2 levels?
regulates initiation of transcription & amount of transcription
what is negative transcription control?
what is positive transcription control?
binding of repressor to regulatory DNA sequence— preventing transcription
binding of activator protein to reg DNA, result of initiating gene transcription
what are repressor proteins and what do they bind to?
what does it do to polymerase?
what are the 2 active sites on it?
exert negative control on transcription when they are active and bind to the repressor
binds on reg DNA where the polymerase would bind OR by preventing the transcription complex
DNa binding domain– locating & binding operator DNA
allosteric domain— binds a molecule & changes conformation
inactivated by inducer binding to allosteric site
what may some repressors need to activate DNA bidding site?
corepressor
what is positive control of transcription controlled by?
what do activators do?
what site do they have?
activator proteins that bind on activator binding sites
OR
Bind to repressors which make them disassociate
binding to repressor makes it leave & allows RNA pol binding at the promoter & intimate transcription
DNA binding site
some activators need a ____ to activate the DNA binding domain, then ___ happens, allowing for binding to DNA
allosteric effector compound
allosteric change
what happens if activator binds an inhibitor?
will not bind to DNA
OR
If a repressor, will unbind from DNA
what is a common shape of DNA reg proteins?
what 2 protein segments contact the DNA?
what is the most common structural motif in bacteria?
a helices
-single poly peptide folds to form 2 domains that bind specifically
-reg protein consists of 2 or more polypeptides joined to form a dimer or trimer or more
helix turn helix motif–> 2 alpha helices fit into the major groove of DNA
what are operons ?
genes that are undergoing transcriptional regulation by shared regulatory region
-contain additional regulatory DNA sequences that interact with promoters to exert control
what does glycolysis of glucose produce?
how is lactose made into glucose?
pyruvaqate + ATP
-B galactosidase breaks the B galactoside link to get glucose + galactose
what are the functions of B galactosidase ?
break lactose to glucose + galactose
convert lactose to allolactose– important in regulating transcription of lac operon—-> acts as inducer
what are the regulatory components of the lac operon?
promoter– contains -10 and -35 sites
operator—> lacO–> binds repressor, +1
CAP binding site, on promoter
+++ all partially overlap+++
what are the structural genes of the lac operon and what do they do?
lacz— encodes B galatosidase
lacY—encodes permease, which allows lactose to enter the cell
lac A—transacetylase– not essential for metabolism
Lacl: the repressive
are transcribed as polycistronic mRNA
when does the lac operon function?
when no glucose is available and when lactose is there
if lots of gluecose— repressor bound to the operator
if lots of lactose and NOT glucose—allolactose, which is the inducer, binds the repressor— which makes it unbind the operator, so we have transcription
CAP-cAMP must also bind to CAP binding site
when glucose is available, what is low? what if it is high, what are cAMP levels like?
cAMP–> so not CAP( activator)-cAMP (coactivator) can form and bind to the sit to help with initiation
high cAMP to bind CAP-cAMP–> binds at site & transcription begins
what is catabolite repression?
glucose blocks transcription even when lactose is present
the preferred catabolite –> glucose–> represses transcription
which two complementation groups formed that lac- mutants formed?
what are polar mutations ???
lacZ ( b galactosidase) and lacY (permease)
in lacZ– reduces or preventing translation of other genes sequences in the transcript due to the Shino Dalgrano sequence
what are cis acting factors?
what is cis dominant?
only affect gene expression in the same piece of DNA squence– do not diffuse
ex: promotor, operator
- the only genes the operator is able to influence are the genes located downstream on the same gene
what are trans acting factors?
capable of influencing the expression of genes on other chromosomes
- can diffuse and bind to another target
ex: proteins— repressor, activator
what are the conditions that take place only when glucose is depleted and lactose is present?
cAMP levels rise
CAP-cAMP formation– ->which binds to CAP region on lac promotor
allolactose is produced
repressor protein is modified by allolactose, making it release from the operator, allowing transcription
when does basal transcription occur?
both glucose and lactose is present
What are characteristics of lac superepressor?
Can’t bind inducer molecule
Always binds the operator
Gain of function dom mutation
What is catabolic repression mediated by?
Activator protein binds to promoter
OR
sugar kept out of cell by inactivating permease
