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 answer the question regarding the characteristics of the carbohydrate "Ribose" present in DNA, let's examine each option:

1. A. A pentose sugar
   • Ribose is indeed a pentose sugar. A pentose sugar has five carbon atoms in its molecule. Ribose, in particular, contains an aldehyde group, which classifies it as an aldopentose. In the context of DNA, Deoxyribose, a derived form of ribose with one less oxygen atom, is the sugar present. However, in its basic form, ribose is a pentose sugar. Therefore, this option is correct.
2. B. Present in pyranose form
   • Ribose generally exists in a furanose form, which is a five-membered ring structure. Pyranose refers to a six-membered ring, which is not typical for ribose. Thus, this statement is incorrect.
3. C. In "D" configuration
   • Ribose in biological systems usually exists in the D-configuration. The D and L designations refer to the orientation of the asymmetric carbon furthest from the aldehyde or keto group in Fischer projection. Hence, this option is correct.
4. D. A reducing sugar, when free
   • Ribose, like other aldoses, is a reducing sugar when it is in its free form due to the presence of a free aldehyde group that can be oxidized. Therefore, this option is correct.
5. E. In \( \alpha \)-anomeric form
   • The anomeric form (\(\alpha\) or \(\beta\)) depends on the specific molecule's configuration in solution. While ribose can exist in both configurations in its cyclic form, specifying "\(\alpha\)-anomer" as a characteristic of ribose in DNA is not accurate. Hence, this option is incorrect.

Based on the above analysis, the correct options are A, C, and D only. The characteristic features of ribose that are consistent with the options provided are as a pentose sugar, with D-configuration, and it being a reducing sugar when in free form.

Answer 2

Statement A: Ribose is a pentose sugar, which means it contains five carbon atoms. This is true. Ribose is indeed a pentose sugar, so Statement A is true.

Statement B: Ribose in DNA is primarily found in its furanose form, which is a 5-membered ring structure. It is not found primarily in the pyranose form (6-membered ring). Therefore, Statement B is false.

Statement C: Ribose is found in the D-configuration. Ribose is derived from D-galactose, and thus, it exists in the D-configuration. Therefore, Statement C is true.

Statement D: Ribose is a reducing sugar when it is free (i.e., not part of a nucleotide or in its free form). Ribose has a free aldehyde group in its open-chain form, making it a reducing sugar. Therefore, Statement D is true.

Statement E: Ribose can exist in both \( \alpha \)- and \( \beta \)-anomeric forms, depending on the position of the hydroxyl group at the anomeric carbon. However, it is not always in the \( \alpha \)-form. This statement is not always true. Therefore, Statement E is false.

Conclusion:

The correct answer is \( \boxed{(1)} \), which corresponds to Statements A, C, and D being true.