Ideas for presentation?
Dr Engelbert Buxbaum
engelbert_buxbaum at hotmail.com
Thu Jun 17 03:59:32 EST 2004
Trond Erik Vee Aune wrote:
> I'm going to participate at a "Science Day" in the city where I live,
> and have been asked to make an interactive presentation for children
> from 10 to 19 where the topic is gene technology/microbiology. I can
> borrow some equipment from the lab where I work (general molecular
> biology lab). Do any of you have any ideas what I could do? Ideally it
> should involve the children and trigger their curiosity while being fun
> at the same time.
Chromatography is always a nice topic for science demos. Leaf pigments,
extracted from some weed, separated on paper or on a TLC plate.
Chlorophyll itself is fluorescent, use a slide projector as light
source, with a cobalt glas as excitation monochromator. The
chlorophyll-fluorescence can also be demonstrated in the microscope,
chloroplasts will light up red in blue light.
For a slightly more involved presentation, separate the pigments by
column chromatography and measure their spectrum. Expose a suspension of
motile algae (e.g. _Euglena viridis_) to a spectrum of light and see at
which wavelengths the buggers assemble. Compare this action spectrum
with the spectra of the various pigments. Variation: Project a spectrum
onto a leaf, then stain the starch produced with iodine (this works only
with some species).
Lipids can be extracted e.g. from egg yolk with petrol
ether/iso-popanol (3+2) (less toxic than chloroform/methanol). Dry a ml
of the extract with a little Na2SO4 sicc. Separation is by 2D-TLC on
Kieselgel G plates activated 1 h at 130 degrees C, with 1-butanol/acetic
acid/water 6+2+2 for the first dimension and chloroform/methanol/ammonia
50+40+5 for the second. Carotenes are visible immediately. Exposure of
the plate for a few min to iodine vapours (a few crystals in a
chromatography jar) will stain all lipophilic samples yellow. 1 mg/ml
ninhydrine in water saturated n-butanol heated 10 min at 85 degrees
stains primary amines red (phosphatidyl choline and -serine). Phosphate
reagent (5 ml 60\% HClO4, 10 ml 1 n HCl and 25 ml 4% ammonium molybdate
ad 100 ml) heated 7 min at 85 degrees stains phospholipids blue.
Finally, charring at 130 degrees will give brown spots for all organic
compounds. All staining except the last is transient, the spots need to
be marked while visible. Optional: Use a scanner (or an electronic
camera) after each staining step, and combine the images on a computer
into a false-colour picture.
Of course, other materials may also be used for chromatography, many
inks are mixtures of various pigments, that can be separated on silica
gel plates with the standard butanol/acetic acid/water mixture. But that
would be more chemistry than biology.
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