Which of the following is not relevant to the structure of double helical DNA

Options

A. The helix makes one complete spiral turn every `34Å`
B. The diameter of the helix is `20Å`
C. The distance between adjacent nucleotide is `3.4 nm`
D. Each strands of helix has a backbone made up of alternating ribose sugar and phosphate

Answer

To solve the question "Which of the following is not relevant to the structure of double helical DNA?", we will analyze each option provided and determine which one does not accurately describe the structure of DNA.

### Step-by-Step Solution:

1. **Understanding the Structure of DNA**:
- DNA is a double helical structure composed of two strands that coil around each other. Each strand has a backbone made of sugars and phosphates, with nitrogenous bases attached to the sugars.

2. **Analyzing Each Option**:
- **Option 1**: "The helix makes one complete spiral turn at every 34 angstrom."
- This statement is correct. The double helix of DNA does make one complete turn approximately every 34 angstroms (3.4 nm).

- **Option 2**: "The diameter of the helix is 20 angstrom."
- This statement is also correct. The diameter of the DNA double helix is approximately 20 angstroms (2 nm).

- **Option 3**: "The distance between adjacent nucleotides is 3.5 nanometer."
- This statement is correct as well. The distance between adjacent base pairs in the DNA structure is about 3.4 nm (or 34 angstroms).

- **Option 4**: "Each strand of helix has a backbone made up of alternating ribose sugar and phosphate."
- This statement is incorrect. In DNA, the sugar present is deoxyribose, not ribose. Ribose is found in RNA. Therefore, this option does not accurately describe the structure of DNA.

3. **Conclusion**:
- The option that is not relevant to the structure of double helical DNA is **Option 4**: "Each strand of helix has a backbone made up of alternating ribose sugar and phosphate."

### Final Answer:
**Option 4** is not relevant to the structure of double helical DNA.

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