Final answer:
Glucose and fructose are sugars that form ring structures in solution, with glucose forming a six-membered ring and fructose forming a five-membered ring. The position of the OH group on the anomeric carbon determines the alpha or beta configuration of the glucose ring.
Step-by-step explanation:
Linear and Ring Structures of Glucose and Fructose
Both glucose and fructose are monosaccharides that can exist in two forms: as a linear chain or as a ring-shaped molecule. In aqueous solutions, they predominantly form ring structures. Glucose forms a six-membered ring known as pyranose where an aldehydic group on the first carbon atom reacts with the hydroxyl (OH) group on the fifth carbon atom. This forms a hemiacetal linkage. In the glucose ring, the OH group on the first carbon (anomeric carbon) can be in two different positions: if it's below the plane of the sugar, it's called the alpha (α) position, and if it's above, it's referred to as the beta (β) position.
On the other hand, fructose, which is a ketose sugar, predominantly forms a five-membered ring known as furanose. This occurs when the ketonic group on the second carbon atom of fructose reacts with the OH group on the fifth carbon atom, also forming a hemiacetal linkage. Unlike glucose, fructose has a five-member ring, despite both being hexoses.