Aldose sugar is- A) Ribose B) Ribulose C) Fructose D) None of the above
Hint:Aldose sugars have aldehyde groups present on them. Ribulose and fructose are ketonic sugars. And we know that there is an aldehyde group associated with ribose.
Complete Answer: Aldose is a monosaccharide having a carbon backbone chain in which the last carbon atom has a carbonyl group present on it. Aldose has an aldehyde and a hydroxyl group connected to all the carbon atoms except to the one having carbonyl group. Aldoses differ from ketoses as in ketoses, the carbonyl group is present away from the end of the molecule and therefore are ketones. Simple aldoses like most other carbohydrates have the general chemical formula $C_n(H_2O)_n$. The triose glyceraldehyde is the basic aldose, it contains only three carbon atoms. All aldoses exhibit stereoisomerism due to presence of at least one asymmetric centre carbon. Aldoses can be present in either dextrorotatory form or laevorotatory form. The chirality of the asymmetric carbon is determined on the basis furthest from the aldehyde end, usually the second-last carbon of the chain. d-aldoses are the ones with alcohol groups on the right of the Fischer projection while those with alcohols present on the left are l-aldoses. In nature, d-aldoses are found more abundant than l-aldoses. Glyceraldehyde, erythrose, ribose, glucose and galactose are some of the examples of aldose. Aldoses are classified on the basis of the number of carbons present in the main chain. In order to form a molecule that can be considered as a carbohydrate, minimum 3 carbons in a backbone are required. Carbohydrates with three carbons are named trioses. Glyceraldehyde is the only triose having one chiral stereocenter. There are 2 possible enantiomers, d- and l-glyceraldehyde.
Thus, the correct answer is- A. ribose.
Note: Ribose is carbohydrate, a simple sugar with molecular formula C5H10O5. It is naturally present as d-ribose and is a major component of the ribonucleotides used to synthesise RNA. Ribose is a necessary sugar involved in coding, regulation, decoding and expression of genes.