Gene Regulation in bacteria part 2 Flashcards
Which hypothesis is right?
Hypothesis 1 which states the lacl si a repressor & lacl- mutant is an inactive repressor to yield a constitutive operon
The ________ strain is partial diploid
Merozygote
The ______ strain is hemizygous because its monoploid for lacl & monoploid for operon
Mutant strain
The _______ is heterozygous because its diploid for lacl & diploid for operon (it has lacl- on the chromosome & lacl+ on the plasmid)
Merozygote
In _________ the lacl- is an activator repressor & the lacl+ on the plasmid is an active repressor which inhibits both lac operons
Hypothesis 1
In hypothesis 1 the ______ is on the chromosome where it has no effect (l.o.f.)
lacl-
In hypothesis 2 where the ______ is a constitutive activator the lacl- is on the chromosome (g.o.f.) (activated operon)
lacl-
What are the steps for testing the two hypotheses?
- Grow mutant & merozygote strains separately
- Each strain is divided into two test tube (4 test tubes)
- One of the two test tubes (tubes 2 &4) gets lactose added
- Incubation
- The cells are lyse with sonicator
- The substrate B-ONPG is added where if B-galaclactose is present it will cut it down in the test tube & the tube will turn yellow
- Incubate
- Measure the yellow color produced
What are the results for the mutant strain?
For the mutant strain the lacl- is constitutive where the operon is on without lactose & adding lactose has no effect where the operon stays on
What are the results for the merozygote strain ?
The merozygote strain is het. where the lacl+ is on the plasmid (lacl+ dominated lacl- therefore lacl- is l.o.f.) the operon is off without lactose (consistent with hypothesis 1)
For the ________ strain the lacl+ on the plasmid is inactivated by allolactose where operon is turn on by 200% (consistent with hypothesis 1)
merozygote
Trans-effect
Form of regulation that occurs between two DNA sequences that aren’t adjacent (on the same molecule) (ex. lac repressor on the lac operon)
The lac repressor is a __________ factor (regulates operon)
Trans-acting factor
Cis-acting factor
A DNA segment that is adjacent (on the same molecule) to the gene it regulates (ex. lac operon is a cis-acting factor)
A _________ is caused by genes that encoded regulatory proteins
Trans-effect
________ is caused by DNA sequences that are bound by regulatory proteins
Cis-effect
The ______ mutant is a binding site for lacl so its a cis factors as well
lacO
A mutation in the ________ factor can be rescued by introducing a second gene with normal functions ( a second wild type gene that is het.)
Trans-acting factor
A mutation in the _________ factor can’t be reused by introducing another cis-acting factor with normal function (can’t be rescued by second wild type factor that is het.)
Cis-acting factor
Another way that the lac operon can be regulated is by _________ which is influenced by the presence of glucose where it represses the lac operon
Catabolite repression
In __________ when glucose is gone then the operon is turned on
Catabolite repression
In catalbolite repression glucose isn’t the effector molecule that binds to the regulatory protein but _________ is
Cyclic-AMP (cAMP)
lac operon is regulated _______ & _________
Repressor lacl & activator called CAP
For max transcription repressors are ______ & activators are ______
Off, On
What are the 3 operator sites in lac operon?
- O1 - the operator site is slightly downstream from the promoter
- O2 - is located farther downstream past the lacZ coding sequence
- O3 - is located slightly before from the promoter
So the lac operon can bind to O1 & O2 or to O1 & O3 but never to ________
O2 & O3
When the lac repressor binds to two operator site a ______ must formed
Loop
The lac repressor is a ______ where it has binding sites for each operator site (like dimer such as O3)
tetramer
Because each dimer in the tetramer recognizes a single promoter site, when two dimers are used (like O1 & O3) the tetramer requires that the two operator site are closer together and that is why a ______ forms in DNA
Loop
The loop inhibits RNA polymerase from passing the ____ site & transcribing the operon
O1
