MCB4304 Exam 2 Questions & Answers 2024/2025
lacZ :
lacY :
lacA :
They are all transcribed together to produce one messenger RNA, called a ___ message, starting from a single ___. - ANSWERSlacZ : b-galactosidase; cuts the lactose into glucose and galactose
lacY : lactose (galactoside) p...
They are all transcribed together to produce one messenger RNA, called a ___ message, starting from a
single ___. - ANSWERSlacZ : b-galactosidase; cuts the lactose into glucose and galactose
lacY : lactose (galactoside) permease; allows lactose to enter the cell
lacA : galactoside transacetylase; function unclear
They are all transcribed together to produce one messenger RNA, called a polycistronic message, starting
from a single promoter.
5. Describe and give the results of an experiment that shows that the lac operator is the site of repressor
binding. - ANSWERSWe use nitrocellulose filter binding assay. First, lacO-containing DNA and add an
increasing amount of lac repressor. Assay binding between repressor and operator by measuring the
radioactivity attached to nitrocellulose. Only labeled DNA bound
to repressor would attach to nitrocellulose. Logarithmic curve: repressor bound
in the absence of the inducer IPTG
Barely growing curve: repressor bound in
the presence of 1 mM IPTG, which prevents repressor-operator binding.
B-gal activity can be measured using - ANSWERSX-gal
When all operators are functioning, the repression is 1300 fold.
O2 omitted: lose about __ fold regulation
O3 omitted: lost __ fold
O1: lose about ___ fold --> most impactful in repression - ANSWERSWhen all operators are functioning,
the repression is 1300 fold.
, O2 omitted: lose about 3 fold regulation
O3 omitted: lost 2 fold
O1: lose about 700 fold --> most impactful in repression
Glucose uptake lowers the quantity of cAMP by inhibiting the enzyme ____ which converts ATP to cyclic
AMP - ANSWERSGlucose uptake lowers the quantity of cAMP by inhibiting the enzyme adenylcyclase
Explain the fact that insertion of an integral number of DNA helical turns (multiples of 10.5 bp) between
the araO2 and araI sites in the araBAD operon permits repression by AraC, but insertion of a nonintegral
number of helical turns prevents repression. Illustrate this phenomenon with diagrams. -
ANSWERSBecause insertion of a nonintegral number of helical turns will cause araO2 and araI sites to
not be facing each other and thus araO2 cannot interact with araI.
Does cAMP-CAP promote RNA's open promoter complex? Describe the experiment - ANSWERSYes. If we
add rifampicin and nucleotides to a DNA along with RNA polymerase, no transcription will occur.
However, if we first allow cAMP-CAP complex to bind to the DNA and RNA polymerase, then add
rifampicin and nucleotides, transcription will occur because the c-C complex promoted an open
promoter complex.
List evidence used to support the direct interaction model between cAMP-CAP and the C-terminal
domain of the RNA polymerase subunit. - ANSWERS1. co-sedimentation
2. chemical cross-linking
3. Dnase footprinting
4. Mutations in CRP that decrease activation but NOT DNA binding
How does cAMP-CRP binding to the activator site facilitate binding of polymerase to the promoter? -
ANSWERS1. cAMP-CRP complex "touches" the polymerase --> cooperative binding
2. cAMP-CRP causes the DNA to bend.
More recent studies have shown that repressor/polymerase : operator interactions are in ____. -
ANSWERSMore recent studies have shown that repressor/polymerase : operator interactions are in
equilibrium.
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