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BioSc221/325
Exam 3 2006
Name ______________________________
Multiple choice. (2 point each) Choose the one best answer to each of the following questions.
____ 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..
E. It enables the cell to use lactose, even in the absence of the inducer molecule (if necessary).
____ Most prokaryotic promoters have a two-part consensus DNA sequence that consists of a(n) ____.
A. promoter and terminator.
B. –10 and –35 region.
C. activator and operator.
D. promoter and operator.
____ Which of the following is not a mechanism for horizontal gene transfer in nature?
A. conjugation
B. electroporation
C. transduction
D. transformation
____ Genes encoding the enzymes required for synthesis of the amino acid phenylalanine are likely to be controlled by what
type of repressor?
A. inducible
B. repressible
C. constitutive
D. activatable
____ Genes which have a rho independent terminator have what type of signal to indicate transcriptional termination?
A. core enzyme
B. stem loop
C. co-repressor
D. sigma
____ In two-component regulatory systems a signal is relayed to the regulator protein by ____.
A. phosphorylation.
B. adenylylation.
C. autoinducer.
D. a peptide.
____ Natural transformation requires ____.
A. membrane associated transport proteins.
B. circular double stranded plasmid DNA.
C. holes in the membrane.
D. electron transport phosphorylation to generate ATP to drive the transport process.
_____ The function of lactose in controlling expression of the genes of the lactose operon is ____.
A. repressor of the activator protein.
B. activator of the repressor protein.
C. inducer.
D. corepressor.
____ Genes that are expressed at the same level at all times are said to be ____.
A. constitutive.
B. inducible.
C. repressible.
D. activated.
____ Small protein that associates with bacterial RNA polymerase to facilitate promoter recognition and is released during
transcription.
A. alpha factor
B. beta factor
C. gamma factor
D. sigma factor
____ Promoter strength is determined by ____.
A. the DNA sequence of the promoter region.
B. the number of operators.
C. how close the promoter is to the start of transcription.
D. the DNA sequence of the ribosome binding site.
___ Quorum sensing systems use ___ to determine cell density.
A. cell-cell contact
B. autoinducer
C. luminescence
D. phosphotransferase
____ Genes encoding the enzymes required for utilization of fructose as a growth substrate are likely to be controlled by what
type of repressor?
A. inducible
B. repressible
C. constitutive
_____ A repressible operon would most likely be used to regulate ____.
A. amino acid synthesis.
B. DNA replication.
C. sugar metabolism.
D. ATP synthesis.
_____ When studying gene expression, researchers typically use reporter gene “fusions” in which they connect the structural
gene for an enzyme such as -galactosidase (lacZ) to the promoter for the gene they want to study. What is the advantage of
using this system?
A. the reporter gene is smaller than the original gene so it is easier to control than the original gene.
B. the reporter gene codes for an enzyme that is easier to detect (using a simple assay) than the original gene product.
C. the reporter gene is larger than the original gene and therefore more stable than the original gene.
D. the reporter gene codes for a product that is safer than the original gene product.
____ What is the biological function of the tryptophan regulatory system?
A. It allows the cell to make many different amino acids.
B. It prevents the cell from degrading tryptophan.
C. It enables the cell to use tryptophan as a carbon and energy source.
D. It prevents the cell from wasting energy making tryptophan when tryptophan is present in the environment.
E. It enables the cell to make tryptophan (if necessary), even in the absence of the inducer molecule.
____ Which of the diagrams below represent the correct arrangement of molecules at the lactose promoter/operator when
lactose is present (assuming glucose is absent)?
____ From 16S rRNA analysis we have learned that ____.
A.
B.
C.
D.
E.
Archaea and Bacteria are closely related.
photosynthesis evolved in the Archaea.
mitochondria came from the Archaea.
the prokaryotes constitute one of the three domains of life.
the prokaryotes constitute two of the three domains of life.
_____Molecular sequencing suggests that mitochondria arose from a group of prokaryotic organisms called the proteobacteria
which includes the genera Agrobacterium and Rhizobium. This theory is called the ____.
A. endosymbiont theory.
B. ectosymbiont theory.
C. epibiont theory.
D. organelle theory.
E. endocytosis theory.
____ Mobile elements that are flanked with insertion sequences and usually carry a few other genes such as those that confer
antibiotic resistance are called ____.
A. mobilizable plasmids.
B. fertility plasmids.
C. transposons.
D. viral genes.
E. resistance domains.
_____ Max Delbrueck and his colleagues designed an experiment to demonstrate that mutations arise before an organism is
exposed to a selective agent. This type of test was called the ____.
A.variability test.
B fluctuation test.
C. fermentation test.
D. induction test .
____ Which of the diagrams below represent the correct arrangement of molecules at the tryptophan promoter/operator when
tryptophan is not present?
Short answer. (variable points)
In the quorum sensing system that controls light production in the luminescent bacterium Vibrio harveyi the response regulator
protein is called LuxR. LuxR responds to high density as an activator of the lux genes, turning them on at high density. At the
same time, LuxR also represses several genes, turning them off at high density. Describe where the LuxR protein binds to
DNA (relative to the promoter) when it is function as an activator and when it is functioning as a repressor.
Activator
Repressor
What is the difference between a generalized and a specialized transducing phage?
In the lac operon expression of the enzyme -galactosidase is under the control of the lac repressor (LacI) which binds at the
lac operator (lacO). Complete the table with High if -galactosidase is expressed at high levels under the conditions described
or Low if -galactosidase is expressed at low levels under the conditions described. (Assume glucose is not present.)
Mutation
Wild-type (no mutation)
-
lacI - doesn’t make LacI
lacOC - LacI can’t bind the operator
Lactose absent
Lactose present
Irradiated food is generally considered sterile and at least has a very long shelf life. However, Deinococcus radiodurans was
isolated from irradiated meat. How did it manage to survive this "sterilization" process?
One of the diagrams below represents the activity over time of an enzyme involved in the biosynthesis of the amino acid
arginine. At time 0, there is no arginine present and, at a specific time, arginine is added to the culture medium. Circle the
diagram that appropriately represents the activity of the enzyme over time and draw an arrow to indicate the time at which
arginine was added to the culture medium.
Enzyme
Activity
Enzyme
Activity
The bacterium that causes cholera, Vibrio cholerae, produces cholera toxin, which is responsible for the symptoms of the
disease. The gene for the cholera toxin is in a region of the V. cholerae genome that is called a “pathogenicity island” (PI).
The genome of V. cholerae has a G+C content of 47.5% whereas G+C content of the PI is 40%. What is the significance of
this difference?
What is an operon?
Some bacteria, in response to severe DNA damage, produce an “error-prone” DNA repair system which repairs the damage to
the DNA but has a greater tendency to produce errors, leading to mutations. Why might this be an advantage to a bacterium?
Why are ribosomes “popular” targets for antibiotics?
Short Essay Questions. Please answer three of the following four short essay questions (5 points each - 5 bonus points
possible for answering all 4 questions)
Describe three principle methods for lateral gene transfer.
Describe how bacterial gene expression can be controlled at the DNA level, at the RNA level and at the protein level.
Explain why rRNA seems to have been a good choice for studying the relatedness of living organisms. Include in your
explanation, some of the features of the rRNA molecule.
E. coli, when grown on 2 different carbon sources, such as glucose and lactose, exhibits a phenomenon which is referred to as
diauxic growth. Draw a diagram representing a growth curve of E. coli growing under these conditions and explain what is
happening at the various stages.