How many strands or sugar-phosphate backbones are present in a typical DNA molecule?

• A. One
• B. Three
• C. Four
• D. Two

Answer: (D)

Verified step by step guidance

1. Recall the basic structure of DNA, which is composed of two long strands forming a double helix.
2. Each strand consists of a sugar-phosphate backbone with nitrogenous bases attached to the sugars.
3. The two strands run in opposite directions (antiparallel) and are held together by hydrogen bonds between complementary bases.
4. Since each strand has its own sugar-phosphate backbone, a typical DNA molecule has two sugar-phosphate backbones.
5. Therefore, the number of strands or sugar-phosphate backbones in a typical DNA molecule is two.