Question

Which of the following is a keto sugar?

• A. Glyceraldehyde
• B. Fructose
• C. Glucose
• D. Ribose

Answer 1

The correct option is B Fructose

Monosaccharides are the simplest sugars which cannot be hydrolysed further.

Monosaccharides can be divided further based on the number of carbon atoms present into trioses (3C) which include glyceraldehyde (aldose) and dihydroxyacetone (ketose), tetroses (4C) which include erythrose (aldose) and erythrulose (ketose), pentoses (5C) which include ribose (aldose), deoxyribose and ribulose (ketose), hexoses (6C) which include glucose (aldose), fructose (ketose), galactose, etc.

If the structure contains a -CHO (aldehyde) group, it is referred to as aldose sugar and if it contains >C=O (keto) group, it is referred to as ketose sugar. Fructose has a subterminal >C=O group, so it is a keto sugar.
Glucose

Glyceraldehyde
Ribose