brambl at graz.cbs.umn.edu
Mon Sep 12 13:35:45 EST 1994
In article <199409111722.KAA20953 at net.bio.net> npk3325 at VENUS.TAMU.EDU
(Nancy Keller) writes:
> I appreciate all of you who gave me some ideas on teaching labs. & if
> you've got any other neat ideas, please pass by. I'd be happy to share
> those labs that were & weren't successful.
> Nancy P. Keller
Several years ago Salomon Bartnicki-Garcia (bart at ucrac1.ucr.edu) published
(I think in the ASM News) a lab demonstration of dimorphism in Mucor that
is easy and nifty. He cooled agar almost to the point of solidification,
mixed in Mucor spores, and poured the suspension into a plastic beaker.
Later, this beaker was cut in half to reveal a dimorphic cell gradient
from top to bottom (reflecting, presumably, an oxygen gradient) that could
be seen with a low-power microscope. Anyone else tried this?
Another easy demonstration that also can be used in an experimental sense
is an assay of pectinases produced by Rhizopus. This fungus, when grown
as a floating mat on a liquid medium (consisting of sweet potato broth)
produces a powerful pectinase. (Be certain to get a producing isolate of
Rhizopus directly from the surface of any sweet potato.) Then, the
enzymology begins. The enzyme activity assayed directly in the filtered
culture medium or precipitated with ammonium sulfate for concentration. A
simple acoustic assay (quantitative: time-to-endpoint) for enzyme activity
is to prepare uniform thin disks of carrot root that are perforated in the
centers. One hook placed through the perforated disk anchors the enzyme
substrate (the carrot disk) to the bottom of the incubation tube, and
another hook is tied to a string that hangs out of the incubation tube
with a small weight on the other end. Digestion of the plant tissue
causes the weight to drop noisily into a metal pan on the floor. (I know,
I know. This sounds comical, but it works in its primative way.). One can
set up several assays at once to record enzyme protein concentration and
denaturation effects, pH, temperature, culture production curves, etc.).
If nothing else, it teaches a new respect for the discoverers and
suppliers and costs of restriction enzymes.
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