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Name: Allyson
Status: Student
Grade:  9-12
Location: IN
Country: United States
Date: September 2006


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?



Replies:
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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