QUESTION 1 An operon is a cluster of contiguous genes transcribed from a single
ID: 58539 • Letter: Q
Question
QUESTION 1
An operon is a cluster of contiguous genes transcribed from a single promoter giving rise to a ___________ mRNA containing coding sequences for multiple proteins.
polytechnic
polyadenylated
polycistronic
polygamous
5 points
QUESTION 2
Genes whose expression depends on the engagement of an activator protein are said to be ____________ .
negatively regulated
constitutive
positively regulated
unregulated
5 points
QUESTION 3
A strong artificial inducer of the lac operon in is ____________.
Allolactose
X-Gal
Galactose
IPTG
5 points
QUESTION 4
The lac operon contains the gene(s) for the following protein(s) (choose all that apply):
operator
Lac permease
factor
Lac repressor
-galactosidase
Thiogalactoside transacetylase
5 points
QUESTION 5
Match the following structural and regulatory components of the lac operon with their function. Note that not all items will be used.
Determines the site of transcription initiation.
Codes for the lactose transporter (permease).
Binds the CAP protein and allows it to bind to its binding-site on the DNA.
DNA binding site for the lac repressor.
Synthesizes cAMP from ATP.
Codes for the -galactosidase enzyme.
Changes the conformation of the repressor by binding to it.
cAMP
lac repressor
lacZ
Promoter
allolactose
lacY
operator
adenylyl cyclase
5 points
QUESTION 6
Which of the following describes the function of the lacO region of the lac operon?
It encodes for the galactoside permease protein.
It encodes for the Lac repressor protein.
Mutations in this region inhibit expression of the operon, regardless of the presence of absence of the inducer.
It contains the promoter for the operon.
Mutation of this region leads to constitutive expression of the operon.
5 points
QUESTION 7
A strain of E. coli, with a wild-type (WT, "normal") lac operon is often designated I +P +O +Z +Y +A +, where superscripted "+" denotes a normal gene or control element. A mutation in the specific gene or control element is denoted by a different superscript.
Please determine for the following WT and mutant strains what would the levels of -galactosidase ( -Gal) be under the specified conditions. Fill in the blanks in the following table using the following key and the already filled-in examples as a guide:
H: high levels
L: low levels VL: no expression or extremely low levels
Genotype
(molecular interpretation)
+glucose
- lactose
+glucose
+ lactose
- glucose
+ lactose
I +P +O +Z +Y +A +
(WT)
VL
L
H
I +P +O +Z -Y +A +
(deletion in the middle of Z)
VL
VL
Blank 1
I +P +O cZ +Y +A +
( O with scrambled sequence)
Blank 2
Blank 3
Blank 4
I -dP +O +Z +Y +A +
(repressor's DNA binding domain is defective)
Blank 5
Blank 6
Blank 7
I sP +O +Z +Y +A +
(repressor's allolactose binding domain is defective)
Blank 8
Blank 9
Blank 10
15 points
QUESTION 8
In bacteria, the cya gene encodes the adenylate cyclase protein. When cultured in conditions of low glucose and high lactose, would you expect the expression of ß-galactosidase to be different between the cya– mutant strain and the wild-type strain?
Yes, ß-galactosidase expression will be entirely absent from the cya– mutant but actively transcribed in the wild-type strain.
No, ß-galactosidase expression will be low in both bacterial strains.
Yes, ß-galactosidase expression will be lower in the cya–mutant as compared to the wild-type strain but will still be expressed in both.
Yes, ß-galactosidase expression will be higher in the mutant as compared to the wild-type, but it will still be expressed in both.
No, ß-galactosidase expression will be high in both bacterial strains.
5 points
QUESTION 9
Fill in the following table with the appropriate option for each column in regard to a mutant E. coli strain the produces a lac repressor that cannot bind the inducer but is otherwise normal (IdibP+O+Z+Y+A+ ).
Glucose
+/-
Lactose
+/-
cAMP
low/high
CRP(CAP)
bound/free
Repressor
bound/free
-galacotosidase activity
very low/low/high
+
-
low
Blank 1
Blank 2
Blank 3
+
+
Blank 4
free
Blank 5
Blank 6
-
+
Blank 7
Blank 8
Blank 9
Blank 10
15 points
QUESTION 10
Glucose exerts its inhibitory effect over the lac operon (so called catabolite repression) by inhibiting the activity of the enzyme that converts ____________ to ____________.
dAMP to cAMP
cAMP to ATP
cAMP to dAMP
ATP to cAMP
5 points
QUESTION 11
In Figure 3, the levels of glucose in the medium and -galactosidase (-gal) in the cells are plotted together with the growth curve from Figure 1. Fill in the blanks in the following description of the results as plotted in Figure 3 with terms from the list at the bottom (not all terms are used, and some may appear more than once).
Following a short Blank 1, the bacteria enter the Blank 2 and divide rapidly leading to Blank 3 increase in the culture density. Concomitant to the depletion of Blank 4, the culture enters a temporary Blank 5, lasting about 40 min. The culture enters a new Blank 6, which continues unabated for the duration of the experiment. Paralleling this log phase is a dramatic increase in Blank 7.
Choose from: beta-gal, death phase, exponential, galactose, glucose, lactose, lac repressor, lag phase, linear, log phase, stationary phase,
15 points
QUESTION 12
To understand the relationships between the different components of the lac operon Jacob and Monod performed complementation experiments creating partially diploid bacterial cells comprising the genetic material from a mutant with defective regulation of its lac operon and wild-type genetic material (so called "merodiploid analysis"). Which of the following narrations describe results that support that suggested the lac repressor acts in trans to regulate the lac operon:
a non-functional lacI mutant cannot be rescued by a wild-type lacI allele.
a non-functional lacO mutant cannot be rescued by a wild-type lacO allele.
a non-functional lacI mutant is rescued by a wild-type lacI allele.
a non-functional lacO mutant is rescued by a wild-type lacO allele.
5 points
QUESTION 13
Predict the phenotype of mutant E. coli cells (I-) with a deletion encompassing lacI.
Cells will not be able to express -galactosidase, lac permease and thiogalactoside transacetylase neither in the presence nor absence of lactose.
Cells will express -galactosidase, lac permease and thiogalactoside transacetylase in the presence or absence of lactose.
Cells will express -galactosidase, lac permease and thiogalactoside transacetylase only in the presence of lactose.
Cells will express -galactosidase, lac permease and thiogalactoside transacetylase only in the absence of lactose.
5 points
QUESTION 14
The lac repressor and the CAP proteins have similar helix-turn-helix motif in their respective __________________.
Inducer binding sites
DNA binding sites
RNA polymerase binding sites
Lactose binding sites
5 points
QUESTION 15
Which of the following mutations will most likely result in increased levels of -galactosidase in E. coli cells in the presence of both glucose and lactose?
A mutation in the adenylate cyclase that makes it constitutively active.
A mutation in adenylate cyclase making it inactive.
A mutation in the CAP binding site.
A mutation in the catabolite activator protein (CAP) making it inactive.
A.polytechnic
B.polyadenylated
C.polycistronic
D.polygamous
Explanation / Answer
Q 1). c. polycistronic
An operon is a cluster of contiguous genes transcribed from a single promoter giving rise to a ___polycistronic____ mRNA containing coding sequences for multiple proteins.
Q 2). c. positively regulated
Genes whose expression depends on the engagement of an activator protein are said to be positively regulated (if it is repressor protein, then it is negatively regulated).
Q 3). D. IPTG
A strong artificial inducer (synthetic inducer) of the lac operon in is Isopropyl beta-thiogalactoside (IPTG).
Q 4). a. operator
b. lac permease
d. lac repressor
e. -galactosidase
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.