In terms of chemical composition and basic structure, which statement best describes a similarity between RNA and DNA?

• A. Both use thymine (T) as a standard nitrogenous base.
• B. Both are always double-stranded helical molecules under physiological conditions.
• C. Both contain deoxyribose as the pentose sugar in their nucleotides.
• D. Both are polymers of nucleotides linked by $3\prime$-to-$5\prime$ phosphodiester bonds and contain a sugar-phosphate backbone.

Answer: (D)

Verified step by step guidance

1. Recall the basic chemical components of DNA and RNA: both are nucleic acids composed of nucleotides, which include a sugar, a phosphate group, and a nitrogenous base.
2. Identify the sugar in each nucleic acid: DNA contains deoxyribose, while RNA contains ribose. This difference affects their chemical properties and structure.
3. Consider the nitrogenous bases: DNA uses thymine (T), whereas RNA uses uracil (U) instead of thymine.
4. Examine the strand structure: DNA is typically double-stranded and helical under physiological conditions, while RNA is usually single-stranded.
5. Focus on the backbone linkage: both DNA and RNA nucleotides are connected by 3'-to-5' phosphodiester bonds forming a sugar-phosphate backbone, which is a fundamental similarity in their chemical structure.