Download Midterm I Key

CVEN 4484/5484
Environmental Microbiology
Midterm I
February 28, 2003
Name__Marty Microbe
This exam is open book, open note.
Be succinct in your answers, using no more than one or two sentences.
Pace yourself, carefully answer the questions you are sure of before looking up details.
55 minutes allowed.
Scoring
Pg 1 24 pts
Pg 2 24 pts
Pg 3 30 pts
Pg 4 22 pts
Total 100
_24_
_24_
_30_
_22_
100_
Cell classification
1) Is a virus alive? Justify your response using at least two criteria (3pts)
A virus is not alive as it has no means of independent metabolism or
reproduction.
2a) What class of organism is the cartoon below depicting? (2pts)
Gram- Bacteria
b) Label the parts (10pts)
outer
membrane
cell wall
Perplasmic
space
ribosome
granule
plasmid
nucleoid
cytoplasm
cytoplasmic
membrane
porin
3) Circle the eukaryotes listed below (5pts)
anthrax
blue-green algae
fungi
Archaea
frog
4) Give two structural or biochemical characteristics of Archaea that distinguish it from
Bacteria. (4 pts)Various species of Archaea have a 1) single-layer phospholipid
membrane with 2) ether linkages and 3) elevated concentrations of isoprene, and
4) peudopeptidoglycan cell walls
1
Biochemistry of substrates and disruptors
5a) Surfactants belong to what class of macromolecules? (2pts) lipids
b) How do surfactants enhance cell function? (4pts) Surfactant micelles facilitate the
solubilization of hydrocarbon substrates, enhancing bioavailability
c) How do surfactants disrupt cell function? (4pts) Surfactants can disrupt the
cytoplasmic membrane of cells.
6a) What is an epimer? (2pts)An epimer is an isomer that occurs at one of several
carbons in a chain, hexose, for example.
b) Why are isomers important in the context of environmental engineering? (4pts) There
are many xenobiotics that occur as raciemic mixtures (i.e. many isomers mixed
together), some of which be more biodegradable or toxic than others
7a) Which bond has more a greater energy of dissociation: C-C or C=C? (1pts) C=C
b) Which bond has greater entropy (1pts) C-C
Cell functions
8a) What is the common function of spores, oocysts, and cysts? (2pt)
These structures are all survival mechanisms of unicellular organisms formed in
response to environmental stressors such as low substrate availability,
temperature extremes or lack of water.
b) Why do these structures present a challenge in water treatment? (4pts)
Spores, cysts and oocysts protect genetic material inside a thick protein coat that
is resistant to heat, UV light, and disinfectants that target cell membranes and cell
walls.
9) Why is conjugation significant to environmental microbiologists? (4pts)
2
Conjugation results in the recombination of genetic material in cells through DNA
exchange; a consequence of this is the development of resistance to disinfection
and antibiotics.
10) What are the limitations of diffusion for a cell? (4pts)
Diffusion of substrates, ions, and waste products across the cytoplasmic
membrane is the most efficient for a small, spherical cell, which maximizes
surface area to volume. Diffusion across a phospholipid bilayer is limited to small
uncharged particles, Noble gasses and water by energetic constraints.
11a) Transcription and translation vary between Eukaryotes and Bacteria. What is an
outcome of the differences in terms of variety and number of proteins? (4pts)
mRNA in Eukaryotes is split into discrete sections by specialized enzymes,
resulting in more varied and numerous proteins in this class.
12) What is endotoxin? (4 pts)
Endotoxins are highly soluble, toxic chemicals that are produced in the
lipopolysacharide outer membrane of Gram- Bacteria. Endotoxins are the cause
of Bacteria-linked illnesses (e.g., cholera, botulism) in humans.
Cell biochemistry and structures
13) a) Polymerization of monosaccharides is accomplished through glycosidic_
linkages (2pts)
b) Name three structures in a cell that include saccharide polymers (6pts)
polysaccharide granule, cell walls (peptidoglycan and pseudopeptidoglycan),
outer cell membrane (Gram-; lipopolysaccharide), DNA, RNA (polysaccharide
“backbone”)
14a) Protein is a polymer of amino acids (2pts).
b) Name two protein biomolecules in a cell. (4pts)
porins, enzymes
15a) What are the three major structural components of DNA? (6pts)
3
The nucleotide monomer of DNA includes an N-containing cyclical base, a
pentose sugar, and phophate groups
b) What are two places in the cell where DNA is found? (4pts)
DNA is found in the nucleoid or nucleus of a cell and as plasmids in the
cytoplasm
16a) Is the molecule on the following page amphipathic? (1pt) yes
b) Indicate on the diagram the following (5pts)

saturated fatty acid

unsaturated fatty acid

phosphate group

glycerol group

head group [indicate using brackets]
c) Where are you likely to find this molecule? (2pts)
This is a phospholipid and can be found as a structural unit in the cytoplasmic
membrane
d) How might this molecule vary in a solvent-tolerant organism with increasing
concentrations of solvent? (4pts)
A solvent-tolerant cell will increase the number of fatty acids, and the degree of
saturation of fatty acids, in the cell envelope in response to solvent exposure
(Pinkart et al, 1996; App & Env Microbiology 62, 1129-1132; abstract in class
handout). This phospholipid molecule will likely see the saturation of the
unsaturated fatty acid.
4
head group
Phosphate group
glycerol group
Unsaturated
fatty acid
saturated
fatty acid
5