ESGN 586 Midterm Exam Fall 2007
Show all work for complete credit. Name ________________________________
NO Cheat sheets, calculators or electronic devices are allowed. Turn your cell phone, OFF.
1. (10 points) Define:
vibrio: __comma shaped organisms, ~ 1 x 3 µm in length, ex: Desulfovibrio
cell: ___The fundamental unit of living matter.
Enrichment Culture: __A method for isolating microorganisms from nature
using specific culture media and incubation conditions.
Peptidoglycan: __A polysaccharide composed of alternating repeats of
acetylglucosamine and acetylmuramic acid arranged in adjacent layers and
cross linked by short peptides.
Stromatolite: __A laminated microbial mat, typically built from layers of
filamentous microbiota (and other microorganisms) which can become
fossilized.
2. (5 Points) What (things) are needed for life?
Water; a carbon source; an electron donor; and an electron acceptor.
3. (20 points) Explain to your mother what electrophoresis is. Give details (e.g. how to
perform).
At it’s root electrophoresis is the separation of charged molecules in an electric field. DNA,
for example, has a net negative charge. When placed into an electric field, it will ‘run’
through a matrix toward the positive cathode. That matrix can be something like a 1%
agarose gel for basic determination of DNA presence; to a polyacrylamide matrix for
separation of nucleotides in ‘conventional’ Sanger DNA sequencing. Electrophoresis is
useful for separation of biological macro-molecules such as proteins as well.
To perform electrophoresis:
1. You need to pour a 1 – 1.5% agarose (a polysaccharide sugar from algae) gel.
The agarose is a sol, whose particles never really go into solution, rather, they
fully hydrate and so serve as a molecular sieve for molecules to flow through.
2. You need a buffer to conduct electricity; stabilize the biological molecules; and
one that allows for even flow of the macromolecules. Something like a Tris-
Acetate-EDTA (TAE) buffer, or, a Tris-Borate-EDTA buffer.
3. You make the gels with a comb which makes ‘lanes’ for loading your solutions to
be determined for presence/absence of molecule.
4. You need an indicator in the gel to show presence—for DNA you can use
Ethidium Bromide, which intercalates into the small groove of DNA.
