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BIO NMDCAT Structure of DNA
nmdcat.online July 3, 2026

7. The total diameter of the standard B-form DNA double helix as determined by Watson and Crick is exactly

A. 1 nanometer
B. 2 nanometers
✓
C. 3.4 nanometers
D. 0.34 nanometers

📝 Explanation

The double helix maintains a constant width of 2 nm (20 A˚) because a double-ringed purine always pairs with a single-ringed pyrimidine.

📖 Additional Information

  • 1 nanometer
  • 2 nanometers
  • 3.4 nanometers
  • 0.34 nanometers

The double helix maintains a constant width of 2 nm (20 A˚) because a double-ringed purine always pairs with a single-ringed pyrimidine.

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