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XNA is a laboratory - made nucleic acid ...

XNA is a laboratory - made nucleic acid made of nucleotides in which one component has been replaced by chemical X. The chemical X is not found in nature.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 Which organic component of a DNA or RNA nucleotide has been replaced by X ?

A

Purine base

B

Phosphate group

C

Five - carbon sugar

D

Pyrimidine base

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The correct Answer is:
To solve the question regarding the laboratory-made nucleic acid XNA, we need to analyze the components of a nucleotide and determine which organic component has been replaced by the chemical X. ### Step-by-Step Solution: 1. **Understand the Structure of Nucleotides**: - A nucleotide consists of three main components: a nitrogenous base, a pentose sugar, and a phosphate group. - The nitrogenous bases can be classified into purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). 2. **Identify the Components of DNA and RNA**: - In DNA, the pentose sugar is deoxyribose, while in RNA, it is ribose. - The nitrogenous bases remain the same in both DNA and RNA, except for thymine in DNA, which is replaced by uracil in RNA. 3. **Analyze the Information Given**: - The question states that the part of the molecule responsible for coding is not changed. This indicates that the nitrogenous base, which carries the genetic information, remains the same. - The chemical X is not found in nature, suggesting that it is a synthetic replacement. 4. **Determine Which Component is Replaced**: - Since the nitrogenous base is unchanged, we can eliminate it as the component that has been replaced. - The phosphate group is not considered an organic compound, as it does not contain carbon in the same way sugars and bases do. Therefore, it cannot be replaced by chemical X. - This leaves the pentose sugar as the only component that could be replaced. 5. **Conclusion**: - The chemical X has replaced the pentose sugar in the nucleotide, making it the organic component that has been substituted in XNA. ### Final Answer: The organic component of a DNA or RNA nucleotide that has been replaced by chemical X is the **pentose sugar**. ---
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