What is a common property of glucose, galactose, and fructose?
a) They can all form six-membered rings
b) They are all aldoses
c) They have the same chemical formula
d) They can form the trisaccharide lactose
The correct answer and explanation is:
Correct Answer: c) They have the same chemical formula
Glucose, galactose, and fructose are all monosaccharides, which are the simplest form of carbohydrates. A common property shared among them is that they all have the same chemical formula, C₆H₁₂O₆. This means they are isomers of each other. Even though they have the same number and types of atoms, the arrangement of these atoms in space is different, giving each sugar unique structural and chemical properties.
Glucose and galactose are aldoses, meaning they contain an aldehyde group (-CHO) at the end of their carbon chain. Fructose, on the other hand, is a ketose, containing a ketone group (C=O) typically on the second carbon atom. This difference rules out option (b), since fructose is not an aldose.
Option (a) is also incorrect because although glucose and galactose can form six-membered rings known as pyranose rings, fructose typically forms a five-membered furanose ring in solution, although it can occasionally form a six-membered ring under certain conditions.
Option (d) is incorrect because lactose is a disaccharide, not a trisaccharide. It is formed by the combination of glucose and galactose only. Fructose does not take part in forming lactose. Instead, fructose commonly forms disaccharides like sucrose (with glucose).
In conclusion, the shared feature among glucose, galactose, and fructose is their identical molecular formula, which categorizes them as structural isomers. This commonality underlines how molecules can have the same composition but different structures and functions, a key concept in organic and biological chemistry.