In nucleic acids, what molecules form the backbone of DNA and RNA?

• A. Alternating nitrogenous bases and phosphate groups linked by hydrogen bonds
• B. A continuous chain of amino acids linked by peptide bonds
• C. Alternating fatty acids and glycerol linked by ester bonds
• D. Alternating sugar and phosphate groups linked by phosphodiester bonds

Answer: (D)

Verified step by step guidance

1. Understand the structure of nucleic acids, which are composed of nucleotides. Each nucleotide consists of three parts: a sugar, a phosphate group, and a nitrogenous base.
2. Recognize that the backbone of DNA and RNA is formed by the sugar and phosphate groups, not the nitrogenous bases or other molecules like amino acids or fatty acids.
3. Know that the sugar in DNA is deoxyribose, while in RNA it is ribose. These sugars alternate with phosphate groups to create the backbone.
4. Identify the type of bond that links the sugar of one nucleotide to the phosphate of the next nucleotide. This bond is called a phosphodiester bond.
5. Conclude that the backbone of DNA and RNA is a continuous chain of alternating sugar and phosphate groups connected by phosphodiester bonds, providing structural stability to the nucleic acid.