The substance essential for the synthesis of DNA and RNA is nucleotides. These molecules consist of a nitrogenous base, a sugar (ribose for RNA and deoxyribose for DNA), and a phosphate group. Nucleotides serve as the building blocks for nucleic acids, facilitating the storage and transmission of genetic information. The sequence of nucleotides in DNA and RNA encodes the instructions for synthesizing proteins, which are crucial for cellular functions and organism traits.