Gene expression/Transcription and Lac Operon Flashcards
Transcription regulation in bacteria involves what?
a single activator or repressor
When does transcription and translation occur in prokaryotes?
simultaneously
How does transcription and translation happen simultaneously in prokaryotes?
there’s no membrane bound organelles so mrna gets made and free floating ribosome converts to amino acids
What is RNA polymerase made of?
R subunit core, has two beta, two alphas, 1 sigma and 1 omega factors
What does the sigma factor do?
It positions the enzyme correctly at the promoter and leaves as initiation of the transcription factor occurs
Are sigma factors specialized to promoters? explain what this means?
some sigma factors recognize diff promoters, so yes factors are specialized to promoters
What are the two ways termination occurs?
factor independent termination
Rho dependent termination
Describe how factor independent termination occurs?
If there’s GC rich rna they form a hairpin so weak A rich RNA causes it rna polymerase to be less stable on dna, bumps into hairpin and falls off
How does Rho dependent termination work?
The Rho factor recognizes C rich sequence and releases RNA polymerase
How do bacteria conserve energy?
They only make the enzymes required to produce lactose if it’s in the environment
Whats a promoter?
DNA sequence where RNA polymerase binds to initiate transcription
What are activators? What do they do?
are proteins that bring the RNA polymerase closer to the promoter by binding to activator binding sites, overall promote transcription
What are repressors? What do they do?
Are proteins which block RNA polymerase from binding to the promoter and stops it from moving along RNA, they bind to operators
If the activator doesn’t bind to the activator site what happens?
low-level/basal transcription
What are allosteric effectors?
small molecules that bind to the
allosteric site of regulatory
proteins that bind to the activator site
How do allosteric effectors promote or stop transcription?
If they bind to activator proteins they’ll cause confirmational chnage which lets it bind to activator site and promote transcription, they may also bind to the repressor which cause a change that stops it from binding to the operator
What type of regulation involves a repressor?
negative regulation
What type of regulation involves an activator?
positive regulation
What is an operon?
linked genes under the control of a single promoter
* Functionally-related genes (eg: all involved in lactose metabolism)
* Genes are transcribed onto a single mRNA molecule
* Either all or none of the gene products (enzymes) will be synthesized
What is the lac operon?
: Operon required for the transport and metabolism of lactose
What are cis acting elements in the lac operon?
Promoter, operator, and genes Z, Y
What is Z-?
inactive Z, no matter what won’t make beta glactosidase
What is P-?
RNA polymerase can’t bind, everything after it won’t work
What is Oc?
The repressor can never bind to the operator, so operon is on no matter what
If there’s no lactose present in negtive regulation, what does the repressor do?
binds so operon is off
If there is lactose present, what does the prepressor do?
allosteric effector binds to repressor, stops it from binding to operator, operon is on and inducible
What are F’ plasmids?
plasmids that carry genomic dna
How do we create a merozygote (a partial diploid)?
when we insert a F factor that has left the chromosome it’s integrated in and has picked up some genomic dna which is now an F’ plasmid into an existing bacterial cell (have two copies of dna!)
What is an I- mutation, is it recessive or dominant, cis or trans?
inactive repressor, is recessive and trans
What is an Is mutation? Is it dom or recessive, trans or cis ?
super repressor, dominant over I+, trans
Oc is what to Is?
epistatic, masks effect and repressor can’t bid to operator in Oc.
Do bacteria prefer glucose or lactose?
glucose
If glucose s present what kind of expression do we get from the lac operon?
minimal
If there’s no glucose present what kind of expression do we get from the lac operon?
enhanced
How does glucose effect production of CAMP?
if there’s glucose it stops atp from turning into camp so you get low camp
if there’s no glucose you get high camp
What is CAMP?
an allosteric effector for protein CAP
What is CAP?
catabolite activator protein
What does the CAP-CAMP complex do?
enhances transcription
If high glucose how much CAMP do you get? Does CAP bind? What happens to transcription?
high glucose, no camp, so no cap, so reduced transcription
If low glucose how much CAMP do you get? Does CAP bind? What happens to transcription?
Low glucose, more CAMP, more CAP, more expression
