Lecture 11 Flashcards
Constitutive genes
Housekeeping genes that are expressed continuously by the cell
Inducible genes
Genes that code for inducible enzymes
Which takes fewer steps to metabolize to obtain energy, glucose or lactose?
Glucose b/c lactose needs to break its bond
Do you think E.coli prefers to metabolize lactose, glucose, or both?
Glucose b/c lactose takes more energy to break down
-Glucose directly does glycolysis
Is bacteria polycistronic or monsocistronic
Polycistronic
True or false: the mRNA in eukaryotes is polycistronic
False
Monocistronic
Where does RNA polymerase bind?
Promoter
In the presence of lactose where does the repressor bind?
It does not bind
-if lactose is present then allolactose is also present
-allolactose–>binds to repressor so repressor will not bind to promoter
How does the lac operon prevent RNA polymerase from accessing promoter?
Lac repressor is made from Lacl gene
-repressor binds to the promoter and bends the DNA strand
-Bent DNA strand–>prevents RNA pol from binding
-DNA strand is straight when repressor is off
Diauxic growth
-uses one carbon source over another (glucose over lactose)
Why is there a lag/plateau in growth curve
Metabolic pathway needs to switch/change from glucose to lactose which takes time
True or false: CAP is active without cAMP
False
CAP is only active when bound to cAMP
What regulates cAMP?
cAMP levels depend on phosphoenolpyruvate (PE-P) and the sugar phosphotransferase system
-High glucose levels: glycolysis will occur and PEP turns into pyruvate, no cAMP is made
-Low/no glucose: Phosphate activates adenylyl Cyclase, cAMP is made
Is cAMP synthesized when there is little/no glucose or a lot of glucose
-Little/no glucose
-PE-P transfers phosphoric group to AC (adenyl cyclase)
-cAMP is synthesized
What happens to cAMP and CAP when there is high glucose
CAP is inactive because there is no/low production of cAMP
In low/no glucose CAP is?
Active
In high glucose CAP is?
Inactive
What happens to lac operon when there is HIGH glucose and NO lactose
-Repressor binds–>b/c no allolactose
-CAP is not active b/c cAMP is not made
-No gene expression–>b/c RNA pol cannot bind since DNA is bent
What happens to lac operon when there is LOW glucose and NO lactose
-Repressor binds–>b/c no allolactose
-cAMP activates CAP–>b/c glucose levels are low
-No gene expression–>b/c RNA pol cannot bind since DNA is bent
What happens to lac operon when there is HIGH glucose and LACTOSE
-allolactose IS present–>prevents repressor from binding to promoter
-DNA is no longer bent, RNA pol CAN bind
-Low level/no cAMP b/c high glucose–> does not activate CAP
-Low level of gene expression
What happens to lac operon when there is LOW glucose and LACTOSE
-allolactose IS present–>prevents repressor from binding to promoter
-DNA is no longer bent, RNA pol CAN bind
-cAMP activates CAP b/c low glucose–>CAP helps RNA pol bind
-High level of gene expression
True or False: When CAP is active RNA polymerase cannot bind efficiently to the promoter
False
-When CAP is active RNA pol can bind efficiently to promoter b/c it bends DNA in the correct formation
How is the Lac operon induced first/ Where is allolactose coming from at the beginning?
-Leaky promoter: RNA pol binds & falls off–>overtime produces allolactose
-When there is no lactose–> 10 molecules of allolactose are produced per cell , overtime it accumulates
What does LacZ gene make
B-galactosidase
What does LacY gene encode
lactose permease
What does lacA encode
galactoside transcetylase
What does lacl endode
represser genes
Are lacl and lacZ, lacY, and lacA under the same promoter
No
Lacl has its own promoter
-LacZ, lacY, and lacA are under the same promoter
The lacl gene is a constitutive gene, what does this mean?
The repressor is always on
How does allolactose work?
-binds to repressor
-causes conformational change to repressor
-repressor can longer bind to promoter
