The graphic, The Mucin Pathway, illustrates how the human body makes mucin from glucose.

The pathway graphic consists of three columns.

The main or central column illustrates the various molecular steps that lead to N-Acetylglucosamine and its derivative N-Acetylgalactosamine. The right-hand column lists the names of the various molecules along the pathway and the important enzymes that transform glucose at each step. The left-hand column shows the two small molecules that are added to the glucose derivatives to form the higher molecular weight molecules in the pathway.

Along the bottom is a cartoon of a mucin molecule. Mucin has a protein backbone that accounts for about 20% of the molecular weight. From the backbone are carbohydrate or glycan structures that make up about 80% of the molecule.

The circle to the right shows the linker molecule N-Acetylgalactosamine bound to the protein backbone. N-Acetylglucosamine is the source of
N-Acetylgalactosamine and is essential for the formation of complex glycan structures.

Additional modification steps (not shown) incorporate sialic acid (an N-Acetylglucosamine derivative), galactose (a glucose epimer), fucose and sulphate molecules. These molecules bound to the protein backbone combine with water and give mucin its viscoelastic properties.

It is this layer that provides protection for the gut lining throughout the gastrointestinal tract.