What Class of Biological Molecule Do Guanine, Adenine, Cytosine and Thymine All Belong To?

Nitrogenous bases are the class of biological molecule to which guanine, adenine, cytosine and thymine belong. These nitrogenous bases combine with a five-carbon sugar and a phosphate group to form nucleic acids such as DNA and RNA.

Guanine and adenine belong to the purines, while thymine and cytosine are pyrimidines. A major difference between the two types of nitrogenous bases is their ring structures: Purines have two rings, whereas pyrimidines have a single ring.

NItrogenous bases make up the rungs of the DNA ladder structure. Chargaff's base-pairing rules dictate that two bases pair with one another — a purine to a pyrimidine. In DNA, adenine usually pairs with thymine and cytosine connects to guanine. Two purines cannot join together because the resulting rung would be too long; in the same vein, two pyrimidines cannot pair up because the rung would then be too short. A purine and pyrimidine pair up as the result of hydrogen bonds. In humans, the relative proportions of adenine and thymine are greater than those of cytosine and guanine; these proportions are also true of many eukaryotes.

DNA has subunits called nucleotides. Each nucleotide consists of a phosphate group, the sugar deoxyribose and a nitrogenous base. Alternating sugar and phosphate molecules bonded covalently make up the backbone of the DNA double helix. A nucleoside consists of only the sugar portion bonded to a nitrogenous base.