This guide to a graphical representation of human milk oligosaccharide (HMO) structures follows that presented by Lars Bode (Bode2012). Sugar units within the HMO are represented by shapes and the configuration of glycosidic linkages are shown between these shapes. HMOs are made up of 5 monosaccharides: three of these, i.e. glucose (), galactose (), N-acetylglucosamine (), form the backbone or core of the oligosaccharide; the other two, fucose () and a sialic acid - which is predominately 5-N-acetylneuraminic acid () - are enzymatically added subsequently.

1. The vast majority of HMOs contain lactose,

2-1. Type 1 chains extend a lactose unit with a lacto-N-biose: . Addition of this disaccharide terminates the chain.

2-1-1. Elongation can occur at the 3'-position of lactose to give lacto-N-tetraose (LNT):

2-1-2. Branching can occur at the 6'-position of lactose to give lacto-N-hexaose (LNH):

2-2. Type 2 chains are created when an N-acetyllactose, , is added to a lactose unit. This can be extended further with either another N-acetyllactose or lacto-N-biose dissacharide.

2-2-1. Lacto-N-neotetraose (LNnT) is formed by a 1,3-link:

2-2-2. Lacto-N-neohexaose (LNnH) has additional branching:

2-2-3. A branched extension produces iso-lacto-N-neooactaose:

2-2-4. A linear extension can produce para-lacto-N-octaose terminated by a lacto-N-biose:

3-1. Lactose or elongated oligosaccharides (above) can be fucosylated,, at α-1,2, α-1,3 or α-1,4 positions.

3-1-1. Simple lactose can be fucosylated at the 3-position to form 3-fucosyllactose: , or 2'-position to form 2'-fucosyllactose:

3-1-2. Fucosylation of oligosaccharides can occur internally, at either terminal, on a glucose, galactose or N-acetylglucosamine unit.

3-1-2-1. Internally on N-acetylglucosamine: lacto-N-fucopentaose II,

3-1-2-2. Reducing terminal on glucose: lacto-N-fucopentaose V,

3-1-2-3. Terminal on galactose: lacto-N-fucopentaose I,

3-2. Similar to fucosylation, lactose or the elongated oligosaccharides can be sialylated,, but only at α-2,3 or α-2,6 positions.

3-2-1. Simple lactose can be sialylated at the 3'-position to form 3'-sialyllactose: , or 6'-sialyllactose:

3-2-2. Sialylation of oligosaccharides can occur internally, or at the non-reducing terminus, and on a galactose or N-acetylglucosamine unit.

3-2-2-1. Internally on N-acetylglucosamine: lactosialyl-tetrasaccharide b (LST b),

3-2-2-2. Terminally at a galactose residue: lactosialyl-tetrasaccharide a (LST a),

3-2-2-3. Disialylated: disialyllacto-N-tetraose (DSLNT),