The building blocks consisting of sugar phosphate, and nitrogen base are called nucleotides. Nucleotides are the basic structural units of nucleic acids (DNA and RNA). Each nucleotide consists of:

- A nitrogen-containing base (either a purine or pyrimidine)

- A five-carbon sugar (either ribose or deoxyribose)

- A phosphate group

The nitrogenous bases are classified into two types: purines and pyrimidines. Purines include adenine (A) and guanine (G), while pyrimidines include thymine (T), cytosine (C), and uracil (U). Uracil is found in RNA, while thymine is found in DNA.

Nucleotides are linked together to form polynucleotide chains, which are the building blocks of nucleic acids. The sequence of nucleotides along the polynucleotide chain determines the genetic information encoded in the nucleic acid.