Microbiology Exam #3
April 11, 2008
Name:____________________________________
Matching (30 pts)
Choose the best definition for each term below.
____ Operon
Regulon
Operator
Repressor
Co-repressor
Inducer
____ Activator
A.
B.
C.
D.
E.
F.
G.
Several unlinked genes controlled by the same regulator.
Regulatory element where a repressor protein binds.
Small molecule which binds to an apo-repressor.
Protein which binds to DNA to block transcription.
Protein that enhances RNA polymerase activity.
Several genes controlled by the same promoter.
Small molecule which binds to a repressor.
Match the mechanism for horizontal gene transfer with its description.
Conjugation
Transposition
Transduction
Transformation
A.
B.
C.
D.
Virus mediated gene transfer
Uptake of naked DNA from the environment.
Transfer of a plasmid via a mating bridge.
Transfer of DNA fragments between two insertion
sequences
Match the organelle with its likely microbial origin
Mitochondrion
Chloroplast
Flagellum
Hydrogenosome
A.
B.
C.
D.
anaerobic or aerotolerant proteobacterium
oxygenic phototroph
spirochaete
aerobic chemoheterotroph
Multiple Choice (30 pts)
Select the ONE best answer
____ The stem-loop structure formed at the end of an mRNA molecule would be called a(n)
A.
B.
C.
D.
E.
Terminator
Stop codon
Rho molecule
Anti-activator
Inhibitor
____ A mutation in the operator of a gene for heme biosynthesis results in constant production
of heme (an Oc mutation). Expression is constant because
A.
B.
C.
D.
The RNAP now has a higher affinity for expressing the gene.
The repressor can no longer turn off expression.
The activator is constantly bound to the DNA.
Inducer continuously binds to repressor preventing repressor binding
____ A mutation in the gene encoding the lactose repressor (lacI) that prevents lactose from
binding to the LacI protein would result in
A.
B.
C.
D.
Constant expression of the lac operon in the absence of lactose
Constant repression of the lac operon in the absence of lactose
Constant expression of the lac operon in the presence of lactose
Constant repression of the lac operon in the presence of lactose
____ How does catabolite activation influence gene expression?
A. When glucose levels are high, cAMP levels are high enough to bind CAP and activate
expression.
B. When glucose levels are high, cAMP levels are low enough to not bind CAP and
activate expression.
C. When glucose levels are low, cAMP levels are high enough to bind CAP and activate
expression.
D. When glucose levels are low, cAMP levels are low enough to not bind CAP and activate
expression.
____ What is the biological function of the lactose regulatory system?
A. It allows the cell to use many different types of carbohydrates.
B. It prevents the cell from using lactose.
C. It enables the cell to efficiently use its metabolic machinery to degrade glucose and
lactose simultaneously.
D. It prevents the cell from wasting energy making lactose-degrading enzymes when
lactose is not present in the environment.
____ Which of the following regulatory schemes is also called density dependent regulation?
A.
B.
C.
D.
Quorum sensing
Two-component regulation
Catabolite activation
Co-repression
____ Why are two-component regulatory systems particularly useful for controlling gene
expression in response to environmental signals?
A.
B.
C.
D.
Two proteins controlling a gene means there are two chances to activate a gene.
Two proteins delay the response time so the cell can be sure the change is permanent.
One of the two proteins can be exposed to the external environment to receive a signal.
Phosphorylation is a permanent change so genes are always turned on after signal.
____ What kinds of genes are typically found on plasmids?
A.
B.
C.
D.
E.
Antibiotic resistance genes
Genes for biodegradation pathways
Virulence genes
All of the above
None of the above
____ What is an auxotroph?
A.
B.
C.
D.
Another name for a phototroph.
Another name for a wild-type strain.
An organism with a mutation in a biosynthetic gene that requires a specific nutrient.
An organism with a mutation in a degradative pathway that can no longer use a carbon
source.
____ In Avery’s experiment in which he showed that DNA is the genetic molecule, the
acquisition of the virulence genes would be an example of
A.
B.
C.
D.
Transformation
Transduction
Conjugation
Electroporation
____ What other enzyme is often associated with a restriction endonuclease in bacterial cells?
A.
B.
C.
D.
DNA methylase
DNA ligase
DNA polymerase
RNA polymerase
____ What is genome annotation?
A. Adding new sequences to an incomplete genome sequence.
B. Comparing genome sequences of related organisms.
C. Determining the potential function of a gene product by its similarity to genes from other
organisms.
D. Eliminating genes with unknown function
____ When studying gene expression using DNA microarrays ___.
A. mRNA is copied to make fluorescently labeled cDNA which is then hybridized to the
DNA on the microarray.
B. cell are grown in the presence of fluorescent dyes which are incorporated into mRNA
and the mRNA is then hybridized to the DNA microarray.
C. fluorescently labeled proteins bind to their corresponding DNA sequence.
D. each gene from the cell is cloned into a plasmid and the plasmids are isolated and then
hybridized to the DNA microarray.
____ The genome sequence of a bacterium reveals several regions in which the average G+C
content is significantly different than the rest of the genome. What is the significance of this
observation?
A.
B.
C.
D.
The region was likely acquired by horizontal gene transfer.
The bacterium is a new species.
The bacterium is a thermophile.
The bacterium is a pathogen.
____ Herpes virus is an enveloped virus but it does not bud from its host cell. Where does it
get its envelope?
A.
B.
C.
D.
From the host endoplasmic reticulum.
From the host golgi apparatus.
From the host nucleus.
From the host phagocytic vesicle.
Short Answer (22 pts)
Addition of
substrate
Enzyme Activity
The figure at the right, illustrates expression of
enzyme activity for a catabolic pathway that is
regulated by an inducible repressor system.
On the two lines below, draw the position of
RNAP (
), Repressor (
), and inducer (
(if present) at both t0 and t3.
)
0
1
2
3
Time (hrs)
4
t0
P
O
Z
Y
A
P
O
Z
Y
A
t3
What is an autoinducer?
Why do organisms such as Vibrio fischeri use quorum sensing to control bioluminescence?
What is the difference between generalized and specialized transduction?
On what is the three-domain concept of life based?
What is a gene library?
Describe one traditional method of classifying bacteria (prior to 16S sequencing) and the
drawbacks to that method.
Why must all negative stranded RNA viruses package an RNA replicase in their capsid?
Why are the cellular slime molds used as a model system for development?
How do haploid eukaryotic microbes ensure that sexual reproduction leads to genetic
diversity?
Short Essay (18 pts)
Answer 3 of the 4 questions below. 6 pts each.
6 bonus points possible for answering all 4.
The ideal antimicrobial drugs target unique characteristics of the organism to be inhibited. This
makes it much more difficult to design drugs against eukaryotic microbes. We have discussed
a few strategies in class. Describe a potential drug target in a eukaryotic microbe and how that
target might be inhibited. What makes that characteristic unique to that particular microbe and
what function does it serve for the organism that possesses it?
Describe the “decision” bacteriophage lambda makes between lysis and lysogeny. What
proteins are involved in the decision making process? How can lysis occur if a lambda phage
has already formed a stable lysogeny?
Describe how 16S rRNA gene sequences are used in establishing prokaryotic taxonomies.
What features of the rRNA genes are critical for isolating and sequencing genes from
uncultured prokaryotes? What are the steps involved in generating 16S rRNA gene
sequences and using them to determine relatedness of prokaryotes?
Describe 4 different types of plasmid vectors used in gene cloning. What unique
characteristics do they possess and how are they used in studying cloned genes?