In DNA structure, what chemical components form the repeating backbone of the DNA double helix?

• A. A continuous chain of hydrogen-bonded base pairs
• B. Alternating deoxyribose sugars and phosphate groups linked by phosphodiester bonds
• C. Alternating nitrogenous bases linked by peptide bonds
• D. Alternating ribose sugars and phosphate groups linked by glycosidic bonds

Answer: (B)

Verified step by step guidance

1. Understand the structure of DNA: DNA is composed of nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base.
2. Identify the backbone components: The backbone of DNA consists of alternating sugar and phosphate groups, which provide structural support.
3. Recognize the sugar type: In DNA, the sugar is deoxyribose, not ribose (which is found in RNA).
4. Understand the type of bonds: The sugar and phosphate groups are connected by phosphodiester bonds, forming a strong, covalent linkage.
5. Clarify the role of bases: Nitrogenous bases are attached to the sugar but are not part of the backbone; they pair via hydrogen bonds to form the rungs of the double helix.