BIOL 438 Exam 2 Review Questions and
Complete Solutions
Suppose that you made a special mutation in the laci protein that blocked its binding to
allolactose but did not affect its ability to bind to laco.
What effect would this mutation have on:
A) the expression of the lac operon?
B) the ability the cell to use lactose as carbon source? ✅a. Eliminate expression
because it will not be transcribed
B. Unable to use lactose as a carbon source
Positive control Operons ✅-have poor promoters (absent -35 promoter)
-need transcriptional activators to assist binding of RNA polymerase to the poor
promoters
-operators usually before the promotor
Activator proteins: 2 confirmations
-one that bind to the operator and assists promoter recognition by RNA polymerase
-one does not interact with DNA or RNA polymerase
Ara operon ✅arac: positive regulator
-also has negative regulatory function: when L-arabinose is not present, it functions as a
repressor by blocking the binding of RNA polymerase to the P(BAD) promotor
Arabad: operon
P(BAD): promotor
Ara operon process ✅-arac binds arai1 in the absence of arabinose
-arac binds both arai1 and arai2 in the presence of arabinose and then assists RNA
polymerase to bind the promoter
-Arac binds arao1 in the presence of arabinose and acts as a transcriptional activator
for arac leading to increased synthesis of arac
2 component regulatory system ✅Prominent regulatory mechanism by which
organisms couple environmental signals to specific adaptive responses, most
commonly the expression of genes.
Consists of:
-signal sensor
-signal transducer (regulates some cellular response)
Usually via positive control
2 component responses ✅-nutrient acquisition
Complete Solutions
Suppose that you made a special mutation in the laci protein that blocked its binding to
allolactose but did not affect its ability to bind to laco.
What effect would this mutation have on:
A) the expression of the lac operon?
B) the ability the cell to use lactose as carbon source? ✅a. Eliminate expression
because it will not be transcribed
B. Unable to use lactose as a carbon source
Positive control Operons ✅-have poor promoters (absent -35 promoter)
-need transcriptional activators to assist binding of RNA polymerase to the poor
promoters
-operators usually before the promotor
Activator proteins: 2 confirmations
-one that bind to the operator and assists promoter recognition by RNA polymerase
-one does not interact with DNA or RNA polymerase
Ara operon ✅arac: positive regulator
-also has negative regulatory function: when L-arabinose is not present, it functions as a
repressor by blocking the binding of RNA polymerase to the P(BAD) promotor
Arabad: operon
P(BAD): promotor
Ara operon process ✅-arac binds arai1 in the absence of arabinose
-arac binds both arai1 and arai2 in the presence of arabinose and then assists RNA
polymerase to bind the promoter
-Arac binds arao1 in the presence of arabinose and acts as a transcriptional activator
for arac leading to increased synthesis of arac
2 component regulatory system ✅Prominent regulatory mechanism by which
organisms couple environmental signals to specific adaptive responses, most
commonly the expression of genes.
Consists of:
-signal sensor
-signal transducer (regulates some cellular response)
Usually via positive control
2 component responses ✅-nutrient acquisition
