Question

Sugar present in DNA is

• A. $\beta$-D-2-ribose
• B. $\beta$-D-2-deoxyribose
• C. $\alpha$-D-2-ribose
• D. $\alpha$-D-2-deoxyribose

Hint:

DNA contains the sugar 2-deoxyribose. RNA contains the sugar ribose.
Both are D-sugars.
The N-glycosidic bond linking the sugar to the base is in the $\beta$-configuration in both DNA and RNA.
Thus, sugar in DNA is $\beta$-D-2-deoxyribose.
Sugar in RNA is $\beta$-D-ribose.

Answer 1

The Correct Option is B

DNA stands for Deoxyribonucleic Acid. The sugar component of DNA is a pentose (5-carbon) sugar called deoxyribose. Specifically, it is 2-deoxyribose, meaning it is derived from ribose by the removal of an oxygen atom from the hydroxyl group at the 2' position (carbon atom 2 of the sugar ring). The structure of ribose and deoxyribose in their furanose (5-membered ring) form is important. In nucleic acids, the sugar is D-ribose or D-2-deoxyribose. The 'D' refers to the D-series of sugars. The anomeric configuration (alpha or beta) of the N-glycosidic bond linking the sugar to the nitrogenous base is also specific. In naturally occurring nucleotides and nucleic acids, this bond is in the $\beta$ configuration. This means the base is "up" relative to the CH$_2$OH group (C5') if the ring is drawn in a standard orientation (Haworth projection with ring oxygen at the back top). So, the sugar present in DNA is $\beta$-D-2-deoxyribose. \begin{itemize} \item $\beta$: Refers to the configuration at the anomeric carbon (C1'). The N-glycosidic bond is $\beta$. \item D: Refers to the D-family of sugars (based on the configuration of the highest numbered chiral carbon relative to D-glyceraldehyde). \item 2-deoxyribose: Indicates that the sugar is ribose lacking an oxygen atom at the C2' position (i.e., C2' has -H, -H instead of -H, -OH as in ribose). \end{itemize} Therefore, the sugar in DNA is $\beta$-D-2-deoxyribose. RNA contains $\beta$-D-ribose. \[ \boxed{\beta \text{-D-2-deoxyribose}} \]