Download BISC403 Genetic and Evolutionary Biology Spring, 2011 May 16

BISC403
Genetic and Evolutionary Biology
Spring, 2011
May 16, 2011
Summary of requirements for Exam 4 (to be given on May 24) plus exam 4 from fall,
2010
The primary responsibility is for any topic covered in lecture. This will include those
portions of the textbook which relate to the lecture.
Reading: (note that figure references always carry with them the focus on the associated
text)
Chapter 15:
Section 15.1
Section 15.2 through first half of page 533. Figure 15.25 covers the last assigned
portion.
The remainder of section 15.2 and all of section 15.3 are NOT assigned.
Chapter 9:
Section 9.1
Section 9.2
Section 9.3
Chapter 11:
Section 11.1
Section 11.2 through first paragraph of page 375. Figure 11.6 covers the last
assigned portion.
Section 11.3 up to but not including section “Large-scale …” on bottom of page
381. Figure 11.13 covers the last assigned portion.
Aside from the specific topics listed above, any topics in these chapters which were not
covered in lecture will not be on the examination.
Problems to be studied:
I on page 545 ("Solved Problems")
15.11, 17.13
The only portions of last fall’s fourth exam which are relevant for this spring are
questions 20 through 30 plus 32 and 33. The topics covered by the first 19 questions
and number 31 from last fall were on exam 3 this spring. The topics that were
covered after operons this spring were not on last year’s exam.
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EXAM 4, FALL, 2010
20.
a)
b)
c)
d)
e)
The following figure displays the fundamental experimental results with wild type
E. coli that gave rise to the Lac operon model.
Assuming that both glucose and lactose were present at the start of the
experiment, which of the following is true?
During the first growth phase, the presence of glucose indirectly prevents the
transcription of the Lac operon.
When glucose is depleted at the end of the first growth phase, lactose gains the
ability to bind to the repressor protein.
When glucose is depleted and the first growth phase ends, adenyl cyclase activity
is decreased, stimulating transcription of the Lac operon.
The sequential consumption of glucose, then lactose would not be observed in
cells which had a mutation and became Lac I -.
a and c.
3
21.
a)
b)
c)
d)
22.
a)
b)
c)
d)
23.
Which of the following is true? (Assume the promoter, operator and structural
genes are all wild type).
lac IS mutants of E. coli are not able to remove the repressor protein from the
operator.
lac I - mutants of E. coli never express ß-galactosidase.
Production of ß-galactosidase is induced by lactose in lac I - mutants of E. coli.
a and c.
c
Consider a cell which is lac IS and o but has wild type lac Z and lac Y genes and
a wild type promoter. What is the phenotype of this cell and why?
The ß-galactosidase gene will never be expressed since lac IS will be dominant in
c
its effect to o
c
The ß-galactosidase gene will be expressed constitutively since o will be
S
dominant in its effect to lac I
The synthesis of ß-galactosidase will not be inducible by lactose because lactose
will not bind to the repressor protein.
b and c.
a)
b)
c)
d)
CRP (also known as CAP) is the cAMP receptor protein (also known as the
cAMP activator protein). Which is the following is true?
CRP monomers are synthesized only in the presence of lactose.
The lac repressor protein blocks the action of CRP.
The dimer of CRP stimulates the binding of RNA polymerase to the promoter.
The dimerization of CRP releases cAMP and therefore stimulates adenyl cyclase.
24.
a)
b)
c)
d)
CRP
will bind to the operator if the promoter is mutated.
blocks the transcription of both anabolic and catabolic operons.
has two domains, one for binding cAMP, one for binding DNA.
only binds to the promoter when glucose is present.
25.
In E. coli with genotype lac IS with all other relevant genes being wild type,
which proteins are bound to the lac operon during the second growth phase after
glucose has been depleted. Assume lactose was present from the start of the
experiment.
only CRP
CRP and lac repressor
only lac repressor
neither CRP nor lac repressor
a)
b)
c)
d)
26.
a)
b)
c)
Which of the following is true?
The promoter operates in a trans fashion while the operator functions in a cis
fashion.
The lac repressor protein operates as a trans-regulator.
Proteins act in cis, but DNA sites act only in trans.
4
d)
'
Partial diploids constructed with F plasmids show trans-regulation for the
promoter.
For questions 27, 28 and 29, the following abbreviations are used for 5 genes
related to lactose metabolism:
I = Lac I, the gene for the lac repressor
p = promoter (the genotype p- indicates a deletion of the promoter)
o = operator
Z = Lac Z, the structural gene for ß-galactosidase
Y = Lac Y, the structural gene for lactose permease
27.
a)
b)
c)
d)
28.
a)
b)
c)
d)
29.
a)
b)
c)
d)
30.
a)
b)
c)
d)
S + c
+
-
Consider an E. coli cell which has genotype (I p o Z Y ). What will be he
phenotype for ß-galactosidase expression?
inducible
constitutive
absent (not expressed under any conditions)
the same as lactose permease expression.
Consider an E. coli cell which is a partial diploid due to the presence of a stable
plasmid carrying the lac operon. If the genotype of this cell for these five genes is
- + + + - + - c + +
(I p o Z Y /I p o Z Y ), what will be the phenotype for ß-galactosidase
expression?
inducible
constitutive
absent (not expressed under any conditions)
the same as lactose permease expression
Consider an E. coli cell which is a partial diploid due to the presence of a stable
plasmid carrying the lac operon. If the genotype of this cell for these five genes is
- + c - + + - + + +
(I p o Z Y /I p o Z Y ), what will be the phenotype for lactose permease
expression?
inducible
constitutive
absent (not expressed under any conditions)
the same as ß-galactosidase expression
The AraC protein stimulates RNA polymerase binding to the promoter in the
arabinose operon:
when arabinose is present in high concentration.
by linking together two copies of the same binding site on the DNA to from a
loop.
after binding to non-adjacent binding sites on the DNA.
when arabinose is absent, so an allosteric shape change cannot take place.
5
Multiple choice answers
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
a
a
d
c
c
b
b
b
a
b
a
32.
Consider an E. coli which had a mutation which prevented cAMP (cyclic AMP)
from binding to CRP monomers. If a culture of this mutant were grown in the
presence of both glucose and lactose, would both sugars be eaten by the bacteria
at the same time or would glucose be eaten first? Explain.
Glucose would be the first and only sugar eaten by this mutant. The CRP has no effect
on glucose utilization, so that would proceed normally. However, the Lac operon
would not be transcribed at all. If cAMP did not bind to the CRP monomers, then the
CRP dimer would not be formed and therefore the promoter would not be in the
appropriate configuration for transcription of the Lac operon.
33.
In the PaJaMo experiment, Pardee, Jacob, and Monod mated an Hfr E. coli of
genotype Lac I+ Lac Z+ and an F- E. coli of genotype Lac I- Lac Z- in a medium
containing no lactose. The expression of ß-galactosidase by the F- cell began
immediately and stopped in 1 to 2 hours. Explain what would have happened to
the pattern of ß-galactosidase expression if the experiment were repeated with an
Hfr strain of genotype Lac I- Lac Z+.
ß-galactosidase would be expressed continuously and not stop after 1 to 2 hours. In
the actual experiment, the production stopped as the wild type Lac I+ gene entered the
recipient. With this mutant, there would only be mutant Lac I- genes in the cell, so no
functional repressor would be present and the operator would remain open.