What do the two molecules ( fructose and glucose ) have in common?

1. Hexoses: Both fructose and glucose are hexoses, meaning they contain six carbon atoms in their molecular structure.

2. Carbonyl Group: They both have a carbonyl group, which consists of a carbon atom double-bonded to an oxygen atom (C=O). In glucose, the carbonyl group is located on the first carbon (C1), forming an aldehyde functional group, while in fructose, it's located on the second carbon (C2), forming a keto functional group.

3. Hydroxyl Groups: Both molecules contain multiple hydroxyl groups (-OH). Glucose has four hydroxyl groups, while fructose has five. These hydroxyl groups contribute to the polarity and solubility of these sugars in water.

4. Cyclic Structures: In aqueous solutions, both fructose and glucose predominantly exist in cyclic forms rather than their linear open-chain forms. These cyclic structures are formed through the reaction of the carbonyl group with a hydroxyl group within the same molecule, resulting in the formation of a hemiacetal ring (in the case of glucose) or a hemiketal ring (in the case of fructose).

Functional Group Differences:

1. Aldehyde vs. Keto: The main difference between glucose and fructose lies in their functional groups. Glucose is an aldose sugar, meaning it contains an aldehyde group (-CHO) on its first carbon atom. Fructose, on the other hand, is a ketose sugar, as it has a keto group (=O) on its second carbon atom.

Taste and Sweetness:

Fructose is sweeter than glucose. The presence of the keto group in fructose allows it to form more extensive hydrogen bonds with water molecules, which reduces its interaction with taste receptors on the tongue, leading to a sweeter perception.

Overall, fructose and glucose share structural similarities as hexoses with hydroxyl groups and cyclic structures. However, they differ in their functional groups, with glucose being an aldose and fructose being a ketose, which influences their sweetness and interaction with taste receptors.