Which of the following best describes the primary structure of a nucleic acid?

• A. The sequence of nucleotides linked by phosphodiester bonds
• B. The association of multiple nucleic acid strands into a complex
• C. The double helix formed by complementary base pairing
• D. The folding of the nucleic acid into a three-dimensional shape

Answer: (A)

Verified step by step guidance

1. Understand the concept of primary structure in biochemistry: The primary structure refers to the linear sequence of building blocks in a biomolecule. For nucleic acids, this means the specific order of nucleotides in the chain.
2. Recall the components of a nucleotide: Each nucleotide consists of three parts: a phosphate group, a sugar (either ribose or deoxyribose), and a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil).
3. Learn how nucleotides are linked: Nucleotides are connected by phosphodiester bonds, which form between the phosphate group of one nucleotide and the hydroxyl group on the sugar of the next nucleotide. This creates a sugar-phosphate backbone.
4. Differentiate primary structure from higher-order structures: The primary structure is distinct from secondary structures (e.g., double helix formed by complementary base pairing) and tertiary structures (e.g., three-dimensional folding). It is solely the sequence of nucleotides.
5. Identify the correct description: Based on the definition of primary structure, the correct answer is 'The sequence of nucleotides linked by phosphodiester bonds,' as this describes the linear arrangement of nucleotides in a nucleic acid.