Cell Membrane Physiology

name        allyson
status       student
grade        9-12
location     IN

Question -   what is the difference in the function of the
proteins and the carbohydrates attached to a cell membrane?
What is the difference in the function of the proteins and the carbohydrates
attached to a cell membrane?
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Many of the proteins in a cell membrane actually have carbohydrates attached
to them as they are secreted through the endoplasmic reticulum and Golgi
apparatus, and these are called glycoproteins.  It's hard to generalize the
function of glycoproteins since they are involved in really diverse
processes such as cell signaling, development, immune response, sperm-egg
recognition, virus-host cell interactions etc and can also play important
roles in making sure a protein folds correctly so it can function.  It's
important to note that glycoproteins can interact with other glycoproteins
or proteins that don't have sugars attached to them.  As an example, many
hormones are peptides with sugars attached to them.  Sugars can also be
attached to lipids (which are the main component of membranes), such as
glycosphingolipids which are also important in immunology and cell
signaling.

Since the sugars attached to glycoproteins can be very heterogeneous,
glycoproteins are harder to isolate and study than proteins without sugars
attached to them. People are still working hard to figure out what the sugar
attachments to many of these proteins actually do, so it's an exciting area
of current research.

Wikipedia doesn't have a great entry for them, but you can look up
glycoproteins on that site.  Also if you're really interested, you can look
up an excellent paper by Ajit Varki of UCSD, the reference is:

Biological roles of oligosaccharides: all of the theories are correct.
Varki A. Glycobiology vol 3 no 2 pp. 97-130, 1993.

Ethan Greenblatt
Stanford Department of Chemistry
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