Question

Ribose is an example of
A) Ketohexose
B) Aldopentose
C) Disaccharide
D) Aldohexose

Answer 1

Ribose is a simple sugar and has a molecular formula as$\text{ }{{\text{C}}_{\text{5}}}{{\text{H}}_{\text{10}}}{{\text{O}}_{\text{5}}}\text{ }$. The monosaccharides which contain the aldehydic group $\text{ }-\text{CHO }$ are called as the aldose and those which contain the ketonic group $\text{ C=O }$ are called as the ketoses. While naming the monosaccharide the prefix indicating the number of carbon atom-like tetra- (4), Penta-(5), hexa-(6) , hepta-(7), etc.is incorporated in the aldoses or ketoses.

Complete step by step solution:
Monosaccharide is the polyhydric aldehyde and ketone which can be hydrolysed into the simpler carbohydrates .the monosaccharides which contain the aldehydic group $\text{ }-\text{CHO }$ are called as the aldose and those which contain the ketonic group $\text{ C=O }$ are called as the ketoses. These are further classified based on the number of carbon atoms in the chain such as triose, tetrose, pentose, hexose, heptose, etc.
The ribose is a simple sugar and has a molecular formula $\text{ }{{\text{C}}_{\text{5}}}{{\text{H}}_{\text{10}}}{{\text{O}}_{\text{5}}}\text{ }$ . The fisher representation of the ribose is as follows,

The structure contains the aldehydic group .Thus it must be an ‘aldose’. The ribose structure contains five carbon atoms in it. We know that, if monosaccharides contain the five-carbon atom we use the prefix for the carbon number as ‘Penta-‘.

The class of the sugar can be simply found by adding the prefix (number of carbon atoms) to the aldose such that Penta drops its ‘a’ and adds in between the aldo and use. Here, the name would be written as,
$\text{ Aldo + penta }-\text{ a + o + se = Aldopentose }$
Thus, ribose is an aldopentose.

Hence, (B) is the correct option.

Note: The ribose 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 ribose).
The glucose can be named aldohexose.