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Carbohydrates are the most abundant biological
compounds. Cells use carbohydrates as structural
building blocks and energy resources. Biochemically,
we recognize three different groups of
carbohydrates, the monosaccharides, the
oligosaccharides, and the polysaccharides. Glucose
is an example of a monosaccharide, sucrose an
oligosaccharide, and starch a polysaccharide.
Monosaccharides can
be further divided and classified into various
groups depending on their chemical structures.
Glucose is a hexose because it contains six carbon
atoms. Ribose, with five carbon atoms, is a pentose.
We also recognize biologically important tetroses
(with four carbon atoms) and trioses (with three
carbon atoms). Monosaccharides may also be
classified as either aldoses or ketoses depending on
the functional groups attached to the molecule. An
aldose, such as glucose, will contain a functional
aldehyde group whereas a ketose (such as fructose)
contains a ketone group.
Although
represented as two-dimensional flat units in most
texts, the carbohydrates form a group of diverse
three-dimensional molecules. Because the carbon
atoms can rotate freely around their chiral centers,
the carbohydrates have a full range of stereometric
isomers.
ACTIVITY
In this activity
you will access Jon Maber's Monosaccharide Browser
and view space-filling projections of
monosaccharides. You will view monosaccharides of
varying structures, both ketoses and aldoses.
Use your browser to
go to
http://www.terravivida.com/vivida/monosaccharide/
Part 1.
Choose
Monosaccharide Browser. It may take a few
moments to load.
1. D-Glucose should
already be on the Browser. What atoms do
the black, red, and grey spheres represent?
2. Use the
Reverse All button to view L-Glucose. How does
D-Glucose differ from L-Glucose?
3. Choose the
Ketose (right under Aldose) to see a six-carbon
ketose. What six-carbon ketose did you view?
4.
How did the ketose
differ from the aldose?
5. Try clicking some of the
other buttons. Describe two other molecules you
find.
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