A nitrogenous (nitrogen-containing) base is a nitrogen-containing molecule having the chemical properties of a base. It is an organic compound that owes its property as a base to the lone pair of electrons of a nitrogen atom. In biological sciences, nitrogenous bases are typically classified as the derivatives of two parent compounds, pyrimidine and purine. They are non-polar and due to their aromaticity, planar. Both pyrimidines and purines resemble pyridine and are thus weak bases and relatively unreactive towards electrophilic aromatic substitution. Their flat shape is particularly important when considering their roles in nucleic acids as nucleobases (building blocks of DNA and RNA): adenine, guanine, thymine, cytosine, and uracil. These nitrogenous bases hydrogen bond between opposing DNA strands to form the rungs of the "twisted ladder" or double helix of DNA or a biological catalyst that is found in the nucleotides. Adenine is always paired with thymine, and guanine is always paired with cytosine. Uracil is only present in RNA: replacing thymine and pairing with adenine.
Famous quotes containing the word base:
“Things base and vile, holding no quantity,
Love can transpose to form and dignity.
Love looks not with the eyes, but with the mind,
And therefore is winged Cupid painted blind.”
—William Shakespeare (1564–1616)