Oligosaccharides often consist of an extended glycan disaccharide. Describe two examples of oligosaccharides that differ in their core disaccharide.

Oligosaccharides are carbohydrates formed by linking a small number (2-10) of monosaccharides together through glycosidic bonds. Disaccharides, a type of oligosaccharides, have only two monosaccharides bonded together. Examples of common disaccharides include sucrose, lactose, and maltose.

Lactose, also known as milk sugar, is a disaccharide composed of the monosaccharides galactose and glucose, linked by a β(1→4) glycosidic bond. So, an oligosaccharide containing lactose as its core disaccharide will have lactose as the main structure and may contain some other monosaccharide residues. One example of a lactose-containing oligosaccharide is Lacto-N-tetraose, which features the disaccharide lactose linked to an N-acetylglucosamine and another galactose residue.

Sucrose is another common disaccharide consisting of the monosaccharides glucose and fructose, connected by an α(1→2) glycosidic bond. An oligosaccharide with sucrose as its core disaccharide will be built around the sucrose structure and may contain additional sugar units. One example of a sucrose-containing oligosaccharide is the raffinose family of oligosaccharides which includes raffinose, stachyose, and verbascose. Raffinose, for instance, contains the core disaccharide sucrose and one galactose linked together by an α(1→6) glycosidic bond. By analyzing and comparing these two examples, we can observe that the lactose-containing oligosaccharide has a core disaccharide of lactose (galactose and glucose), while the sucrose-containing oligosaccharide has a core disaccharide of sucrose (glucose and fructose).