The pentose sugar in `DNA` and `RNA` has the :

Options

A. Open chain structure
B. Pyranose structure
C. Furanose structure
D. None of the above

Explanation

To solve the question regarding the structure of the pentose sugar in DNA and RNA, we will follow these steps:

### Step 1: Understand the Types of Sugars
- **Pentose Sugar**: This is a five-carbon sugar. In the context of nucleic acids, we are specifically looking at two types: deoxyribose (in DNA) and ribose (in RNA).
- **Pyranose vs. Furanose**: Pyranose refers to a six-membered ring structure, whereas furanose refers to a five-membered ring structure.

**Hint**: Recall that the term "pentose" indicates a five-carbon sugar, which will help you distinguish between furanose and pyranose.

### Step 2: Identify the Sugars in DNA and RNA
- **DNA**: The pentose sugar present in DNA is **beta-D-deoxyribose**.
- **RNA**: The pentose sugar present in RNA is **beta-D-ribose**.

**Hint**: Remember that deoxyribose has one less oxygen atom compared to ribose, which is key to understanding their structures.

### Step 3: Draw the Structures
- **Deoxyribose Structure**: When you draw the structure of beta-D-deoxyribose, you will notice it forms a five-membered ring (furanose).
- **Ribose Structure**: Similarly, when you draw the structure of beta-D-ribose, it also forms a five-membered ring (furanose).

**Hint**: Visualizing the structures can help you confirm that both sugars are indeed furanose forms.

### Step 4: Conclude the Type of Structure
- Since both beta-D-deoxyribose (in DNA) and beta-D-ribose (in RNA) are five-membered ring structures, they are classified as **furanose** sugars.

**Hint**: The key takeaway is that both sugars are furanose, which is a direct answer to the question.

### Final Answer
The pentose sugar in DNA and RNA has the **furanose structure**.