Download Exam #2 Bio310 Microbiology F`06 11/15/06

Exam #3 Bio310 Microbiology S’09 4/20/09
NAME:__________________________________
Read each question carefully, some questions contain multiple parts. Point values of
each question are noted in ( ) at the beginning of each question. Ask me if you are
having trouble understanding a question.
1.) ( 5 pts.) Draw out the “Central Dogma” of biology (how does information flow
through a cell? Be sure to label all processes).
DNA  RNA  Protein
(arrows: Transcription & Translation)
2.) ( 4 pts.) Why does a cell need to keep the 2 DNA Pol III complexes together
during replication?
Lagging strand takes longer to synthesize same amount of DNA, so is slower.
Leading strand would rapidly outpace lagging strand complex, eventually creating
large amounts of ssDNA.
3.) (10 pts.) Draw out a DNA replication fork, you do not need to include enzymes,
but must label all nucleic acids and show directionality (5’ & 3’ ends).
Only DNA need be drawn (not enzymes). Be careful with diagram in book as the
stands are labeled wrong! Also, draw strands as straight lines to keep 5’ and 3’ end
labels easier to follow (don’t “twine” strands). Lagging strand must be labeled and
Ozaki fragments must be labeled.
4.) ( 6 pts.) Why is it important for cells to regulate transcription? What selective
advantage does it confer?
Energy efficiency. Bacteria are constantly competing for resources in a niche, the
cell that can survive with the lowest possible energy expenditure will generally
dominate the niche. Regulating transcription saves energy by not transcribing genes
that are not currently needed.
5.) ( 10 pts.) Diagram and briefly explain the mechanism of action of one of the types
of transcriptional regulation in prokaryotes that we talked about in class (also in the
textbook).
Lac operon, Trp operon, or Maltose operon (all in book). Must diagram and label operon
and describe mechanism of regulation.
6.) ( 6 pts.) Why are frameshift mutations so disruptive to gene function?
They change the amino acid sequence through the rest of the gene, usually resulting
in a non-functional or even toxic protein.
7.) (8 pts.) Draw a diagram (with labels) for the lytic life cycle of a bacteriophage
From notes and book (lytic NOT lysogenic)
8.) (4pts.) How can you attack a retrovirus and try to disrupt its life cycle, that
would not be effective against an ordinary DNA virus?
Attach reverse transcriptase or integrase, DNA viruses always lack the first and
often the second enzyme as well.
9 .) ( 9 pts. ) What are the three type of horizontal gene transfer in bacteria, briefly
define each of them.
Transformation, Conjugation, and Transduction (definitions in book and notes)
10.) ( 10 pts.) Describe the Griffith experiment. What did the results of this
experiment suggest (although not prove)?
Diagram or explain experiment. Exp. demonstrated that genetic material can be
transferred from one cell to another, but NOT what that material was.
11.) ( 3 pts. ) What must a plasmid have in order to be passed on vertically (between
generations) in a bacterial population?
an origin of replication
12.) (6 pts.) Define the term: “transposon” and briefly suggest why they are
important to modern molecular biology.
Transposon is a DNA element capable of catalyzing its own excision from one piece
of DNA and reinsertion in another piece of DNA. They can be used to shuttle in new
genes, and are good mutagenic agents, because they usually interrupt the gene into
which they insert (think huge frameshift mutation).
13.) (6 pts.) List and define the two general classes of mutations.
Substitution and Insertion/Deletion mutations (defs in book and notes)
14.) (6 pts) List and briefly describe two techniques for bacterial identification other
than metabolic testing (i.e. you cannot include any of the metabolic tests done in the
lab).
Mass spec: Using a “finger print” pattern of ribosomal proteins to compare to a set
of known samples
Lipids: Use gas chromatography to detect particular types of lipids present in the
cellular membranes.
16 S rRNA: Use PCR to amplify 16 S rRNA and sequence it to compare to
sequences of known organisms in a database.
I also accepted Gram staining, but not cell morphology
15.) ( 6 pts.) Interpret the following metabolic test results. Briefly describe what the
basis for each test is (how does it work).
a.) Your dextrose fermentation tube turned yellow and there is a large bubble in the
Durham tube inside the larger test tube.
Bacteria was able to ferment dextrose and produced organic acids (lowering pH and
changing the color of the tube due to the presence of an acid/base indicator dye) and
gas. Result Acid(+) Gas (+)
b.) After inoculation and a week in the incubator you put your gelatin tube in an ice
bath for ten minutes and it hardened (does not flow when turned upside down).
Bacterium produces gelatinase, which enables it to break down gelatin for food.
Breakdown of gelatin results in the tube staying liquid even when cooled to below its
normal hardening point. Gelatin (+) result