1. Nitrogenous Base: These are the building blocks of the genetic code. There are five main nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T) (found in DNA), and uracil (U) (found in RNA).

2. Sugar: The sugar in DNA is deoxyribose, while the sugar in RNA is ribose. These sugars form the backbone of the nucleic acid molecule.

3. Phosphate Group: Phosphate groups are attached to the sugar molecules and link the nucleotides together, forming the sugar-phosphate backbone of the nucleic acid chain.

These three subunits combine to form a nucleotide, which is the basic building block of nucleic acids. Multiple nucleotides linked together form a polynucleotide chain.