Question

The carbohydrates “Ribose” present in DNA is 
A. A pentose sugar 
B. Present in pyranose form 
C. In “D” configuration 
D. A reducing sugar, when free 
E. In \( \alpha \)-anomeric form

• A. A, C and D Only
• B. A, B and E Only
• C. B, D and E Only
• D. A, D and E Only

Hint:

Ribose in DNA exists in the D-configuration and as a pentose sugar. It is a reducing sugar when free and typically forms a furanose ring, not a pyranose ring.

Answer 1

The Correct Option is A

To address the question about the characteristics of ribose, the carbohydrate found in DNA (though deoxyribose is the specific form), let's evaluate each provided option:

1. A. A pentose sugar
   • Ribose is classified as a pentose sugar due to its five-carbon structure. Specifically, it is an aldopentose, possessing an aldehyde group. While deoxyribose is the sugar in DNA, ribose itself is fundamentally a pentose. This statement is accurate.
2. B. Present in pyranose form
   • Ribose typically adopts a furanose structure, a five-membered ring. A pyranose form denotes a six-membered ring, which is not characteristic of ribose. This statement is inaccurate.
3. C. In "D" configuration
   • Biological ribose predominantly exists in the D-configuration, determined by the orientation of its furthest asymmetric carbon from the aldehyde group in a Fischer projection. This statement is accurate.
4. D. A reducing sugar, when free
   • In its unbound state, ribose functions as a reducing sugar because its free aldehyde group can undergo oxidation. This statement is accurate.
5. E. In \( \alpha \)-anomeric form
   • The anomeric form (\(\alpha\) or \(\beta\)) is dependent on the molecule's configuration in solution. While ribose can exist in both cyclic forms, asserting it is solely in the "\(\alpha\)-anomer" as a definitive characteristic of ribose in DNA is not precise. This statement is inaccurate.

Based on this analysis, the correct descriptions of ribose are A, C, and D. Ribose is characterized as a pentose sugar, possesses the D-configuration, and acts as a reducing sugar in its free state.