Question

What is the class of the monosaccharide ribulose?
A.Ketopentose.
B.Ketohexose.
C.Aldopentose.
D.Aldohexose.

Answer 1

Hint: We know that Monosaccharide is the polyhydric aldehyde and ketone which can be hydrolysed into the simpler carbohydrates. The monosaccharides which contain the aldehydic group are called the aldose and those which contain the ketonic group are called the ketoses.

Complete answer:
Let us study monosaccharides and the structure of pentose and hexose. Monosaccharides are the simplest carbohydrates that cannot be hydrolyzed into smaller molecules. They contain three to seven carbon atoms. There are twenty monosaccharides which occur in nature. These are of two types: Aldose: monosaccharides containing an aldehyde \[\left( -CHO \right)\] group are called aldose. Since the aldehyde group is monovalent, therefore, it is always present at one end of the carbon chain.
Ketose: monosaccharides containing a keto \[\left( >C=O \right)\] group are called ketose. Since the keto group is divalent, it can be present anywhere along the carbon chain. However, in all the naturally occurring ketose, the keto group is always present at a carbon atom next to the terminal carbon. Aldoses and ketose are further classified as trioses, tetroses, pentoses, hexoses, heptoses, etc. according to as they contain three, four, six, seven, etc. Ribulose is a sugar that is obtained by the hydrolysis of the RNA molecule. Ketopentose is the class of the monosaccharide ribulose. It has five Carbon atoms and a keto group.
Therefore, correct answer is option A. i.e. Ketopentose is the class of the monosaccharide ribulose.

Note:
Remember that the ribulose has wide applications in the biological system. It is a base sugar for the nucleosides which builds the DNA or RNA in organisms. The adenosine, cytidine, guanosine and uridine are the ribonucleosides which are derived from the ribose furanose (it is a closed ring ribose structure, Haworth formula of ribulose) and the glucose can be named aldohexose.