In DNA structure, what is the backbone of a DNA strand primarily made of?

• A. Alternating deoxyribose sugars and nitrogenous bases
• B. Alternating phosphate groups and hydrogen bonds
• C. Alternating deoxyribose sugars and phosphate groups (a sugar-phosphate backbone)
• D. Alternating nitrogenous bases and phosphate groups

Answer: (C)

Verified step by step guidance

1. Recall the basic structure of a DNA strand, which consists of a sequence of nucleotides.
2. Understand that each nucleotide is composed of three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base.
3. Identify that the backbone of the DNA strand is formed by the repeating units of sugar and phosphate groups linked together.
4. Recognize that the nitrogenous bases are attached to the sugar molecules and extend inward, pairing with complementary bases on the opposite strand.
5. Conclude that the backbone is made of alternating deoxyribose sugars and phosphate groups, often referred to as the sugar-phosphate backbone.