XNA is a laboratory - made nucleic acid made of nucleotides in which one component has been replaced by chemical X. The chemical X is not found in nature. The part of the molecule responsible for coding is not changed . Which organic component of a DNA or RNA nucleotide has been replaced by X ?

Options

A. Purine base
B. Phosphate group
C. Five - carbon sugar
D. Pyrimidine base

Answer

To solve the question regarding the laboratory-made nucleic acid XNA, we need to analyze the components of a nucleotide and determine which part has been replaced by the chemical X.

### Step-by-Step Solution:

1. **Understanding Nucleotides**:
- A nucleotide is made up of three main components: a nitrogenous base (which can be a purine or pyrimidine), a five-carbon sugar (either ribose in RNA or deoxyribose in DNA), and a phosphate group.

2. **Identifying the Components**:
- The nitrogenous bases are adenine (A), guanine (G) (purines), and cytosine (C), thymine (T) (pyrimidines in DNA), or uracil (U) (pyrimidine in RNA).
- The sugar component can be ribose (in RNA) or deoxyribose (in DNA).
- The phosphate group is consistent in both DNA and RNA.

3. **Analyzing the Question**:
- The question states that in XNA, one component has been replaced by chemical X, which is not found in nature.
- It also mentions that the part of the molecule responsible for coding is not changed. This implies that the nitrogenous bases remain the same since they are responsible for coding the genetic information.

4. **Determining the Replaced Component**:
- Since the nitrogenous bases are unchanged, we can eliminate options related to them (purine base and pyrimidine base).
- The phosphate group is also stated to be similar to that in natural nucleic acids, so it cannot be the replaced component.
- This leaves us with the five-carbon sugar as the only component that could have been replaced by chemical X.

5. **Conclusion**:
- Therefore, the organic component of a DNA or RNA nucleotide that has been replaced by chemical X in XNA is the **five-carbon sugar**.

### Final Answer:
The organic component of a DNA or RNA nucleotide that has been replaced by chemical X is the **five-carbon sugar**.

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