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HOUR EXAM I
BIOLOGY 108
FALL, 2004
In the spirit of the honor code, I pledge that I have
neither given nor received help on this exam.
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1. (12 points) Below is a diagram of a bacterium.
Is this a gram-negative or a gram-positive organism? (circle one)
Label the indicated parts.
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
What is the composition in terms of major macromolecules of
a._____________________________________________
b._____________________________________________
c.______________________________________________
d. ______________________________________________
If this bacterium were of the other type with respect to the Gram stain, what would be 3 major
differences in the cell structure?
1.
2.
3.
2. (16 points) Fill in the following table with respect to bacterial growth.
Organism and
medium
E. coli with
glucose and
nutrient broth
(rich medium)
E. coli with
glucose and
nutrient broth
E. coli with CO2,
NO3, H2SO4 , and
salts
Thiobacillus in
medium with
H2SO3 , and salts
Conditio Growth rate
ns
(fast, medium,
slow, or none)
aerobic
37o
biochemical
Electron
process producing donor
energy
Final electron
acceptor
anaerobi
c
37o
aerobic
37o
aerobic
25o
3. (7 points) Bacterial growth curve
1000
bacterial number
100
10
1
1
2
3
4
5
6
7
8
9
10
11
time (hours)
Identify each of the four phases of bacterial growth shown in the above graph.
A.______________________
B._____________________
C.______________________
D.______________________
What is the doubling time of the cells in phase B (to within 20 min.)? ________________
In which phase are most bacteria in nature? ____________________
4. (4 points) Some bacteria, such as Bacillus subtilis, form spores under conditions in which growth
can no longer be supported. Sporulation has many distinct stages and different proteins are made in
each stage. At the level of transcription, explain how the bacterium regulates transcription so that
the mRNA needed for various sporulation proteinsis made at the correct stages.
5. (7 points) The presence or absence or specific small molecules can influence the level of
transcription of an individual gene. There are 2 major mechanisms of regulation of transcription.
Label the molecules involved in the regulation of the genes below.
argCBH operon
P
O
argC
argB
argH
2.
1.
3.
a. What type of mechanism is depicted above? _______________________
b. Will this scenario lead to transcription? ___________________________
c. What is the corepressor in this system? ____________________________
d. How many proteins will a prokaryote make from this message (when the operon is
expressed) ? ________
6. (17 points) One example of positive control of transcription is the regulation of the maltose
operon. What is the major type of protein involved in positive control? ______________
Fill in the following table (using + and -) to indicate the phenotype of the various E. coli genotypes
listed below.
E. coli genotype
Protein B made
Ability to grow on
minimal media with
In presence of
In absence of
maltose
maltose
maltose
Wild type
A+p+abs+K+B+M-A+p+abs+(ATG of
K) K+B+M-A--p+abs+K+B+M+
A+p--abs+K-B+M-A--p+abs+K+B+M-A=activator, p=promoter, abs=activator binding site, K=maltose transport protein, B=lamB maltose
porin, M=maltase needed to digest maltose, =is a deletion
What would happen if the A+p+abs+K+B+M-- bacterium was infected with lambda?
_____________________
7. (8 points) B. pertussis is the bacteria which causes whooping cough in humans. In order to invade
hosts, B. pertussis must sense its environment and regulate the expression of sets of genes. For
example, B. pertussis makes a toxin only in the presence of host cells. In order to study the
reguation of the production of this toxin, you make a mutant of B. pertussis which no longer makes
toxin. You clone and sequence the mutated gene and find that it encodes a DNA binding protein.
Suggest a hypothesis for how this gene could be involved in the regulation of toxin biosynthesis.
_
In your continued study, you isolate another gene in which mutations abolish toxin biosynthesis.
This gene encodes a membrane protein. Suggest a hypothesis for how this second gene could be
involved in the regulation of toxin biosynthesis.
If your hypothesis is correct what will be the phenotype (with respect to toxin production) of a
mutant
a. in which the first gene is placed behind the lambda PR promoter? _______________________
b. in which the second gene is placed behind the lambda PR promoter? ______________________
8. (8 points) Shown below are the components of the chemotaxis system in E. coli.
cheR
cheW
cheA
Phosphorylation
response
cheB-P
Methylation
sensitivity
cheA-P
cheY
cheY-P
cheZ
Fill in the table with the phenotype of each of the listed mutants.
Mutation
Phenotype
Delete cheA
Delete cheZ
CheY mutant in which the histidine which
is phosphorylated is replaced by glycine
a. In the presence of a constant chemoattractant, E. coli will exhibit _______________
methylation of the receptor transducer proteins.
b. In the presence of an increased chemoattractant, E. coli will exhibit _______________
sensitivity over time.
9. ( 6 points)
a. How does growth in the presence of histidine (an amino acid) effect the amino acid phenylalanine
biosynthetic operon expression in E. coli bacteria with a mutation of Phe t-RNA synthetase so that it
puts histidine on Phe-t-RNA? Describe the mechanism of this regulation.
b. In a trpR-- (R=repressor gene) bacterium, if you deleted region 3 of the attenuator, will tryptophan
biosynthetic enzymes be made in the absence of tryptophan? _____________
In the presence of tryptophan? ___________________
10. ( 7 points) Fill in the following table indicating the major genes in each category for each virus.
virus
T4
T7
immediate early
genes
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
early genes
late genes
Herpes
11. (8 points) Fill out the following indicating the type of plaques (clear, cloudy, or none) which
would be formed if  of the indicated genotype infected the strains of E. coli shown. The genetic
map of  is given below.
PR cro tR1 CII tR2 Q tR3 PRlate SR...A...
______________________________________________________________________
xis att int
CIII tL1 N PL CI PRM
PRE
 genotype
E. coli K12 (-)
wild type
PR no longer binds CI
PR replaced with Ptrp and the
cells are grown on minimal
medium
PRM replaced with Ptrp and the
cells are grown on minimal
medium
bacterial host
E. coli K12 ()