What are the building blocks of nucleic acids?

Nucleic acids, such as DNA and RNA, are fundamentally composed of nucleotides, which serve as their building blocks. Each nucleotide consists of three components: a nitrogenous base, a five-carbon sugar (deoxyribose in DNA and ribose in RNA), and a phosphate group. The arrangement and sequence of these nucleotides carry genetic information and play critical roles in various biological functions, including the synthesis of proteins and the regulation of gene expression.

Other options, while essential in biology, do not form nucleic acids. Monosaccharides are the simplest carbohydrates, primarily involved in energy storage and structural functions in cells. Amino acids are the building blocks of proteins, not nucleic acids. Fatty acids are components of lipids and are involved primarily in energy storage and membrane structure. Thus, nucleotides specifically provide the necessary structure and function that define nucleic acids, making them the correct answer.