The type of molecule that serves as the building block of nucleic acids is called a nucleotide. Nucleotides consist of three components: a phosphate group, a sugar (either ribose in RNA or deoxyribose in DNA), and a nitrogenous base. These molecules link together to form the long chains of DNA and RNA, which are essential for genetic information storage and transfer within biological organisms. Understanding the structure and function of nucleotides is fundamental to the study of genetics and molecular biology.