Glycoproteins are proteins with carbohydrates covalently attached. The predominant sugars found linked on glycoproteins are N-acetylglucosamine (GlcNAc), fucose, mannose, galactose, and sialic acid (N-acetylneuraminic acid). Correctly attaching these sugars through the process of glycosylation is the most extensive post-translational modification made to proteins produced in eukaryotic cells, such as yeast, plant and animal cells. The attachment of these sugars is catalyzed by specific transferases in the lumen of the endoplasmic reticulum and the Golgi apparatus of cells. N-glycans are attached to the amino acid asparagine and share a common core structure that may become branched to terminate in two, three, or four “antennae”. The carbohydrate components of the glycoprotein affect the functionality of the molecule by determining protein folding, solubility, and rate of clearance from the bloodstream. N-glycans, the predominant form of glycosylation on human glycoproteins, are comprised of sugars linked in a specific order, terminating in sialic acid. If the protein is missing these terminal sialic acids, the exposed underlying galactose signals the liver to remove the glycoprotein from circulation.