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Name: Amanda
Status: Student
Age: 16
Location: N/A
Country: N/A
Date: August 2003


Question:
What are homodimeric glycoproteins?



Replies:
Amanda,

If we break down the fancy words, the meaning becomes clear. A dimer is something made up of two subunits (a trimer is made up of three subunits, a monomer has one subunit). So a dimeric protein is made up of two individual protein chains. Now, you could have two of the same thing, say, A and A, or you could have two different subunits, say, A and B. "Homo" means the same, so a homodimeric protein is made up of two identical subunits. If it was made up of A and B, it would be a "heterodimer" or heterodimeric protein.

All that leaves is the "glyco" part. "Glyco-" means "sugar" in biology. Many proteins are modified after they are made. One of the most common modifications is to have one or more short chains of sugars attached to the proteins at certain, specific places in the protein.

So.... a homodimeric glycoprotein is a protein made up of two identical (protein) subunits, with the protein chains modified by having sugar chains on them. Incidentally, glycosylated proteins (i.e., glycoproteins, or proteins modified with sugar chains) and are usually either present on the cell surface, or they are secreted. In other words, the vast majority of proteins inside a human cell are not glycosylated, while the majority of proteins that are secreted are glycosylated.

An example of a homodimeric glycoprotein in your body would be an antibody molecule. Two identical chains of "IgG" are made and brought together inside the cell, modified with sugar chains, and secreted as one large assembly.

Paul Mahoney, Ph.D



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