Principles of Genetics and Breeding

1.2.2.The chemical nature of polynucleotides

By the mid 1940s, biochemists know the fundamental chemical structures of DNA and RNA. When they broke DNA into its component parts, they found these constituents to be nitrogenous bases, phosphoric acid, and the sugar deoxyribose. Similarly, RNA yielded bases and phosphoric acid, plus a different sugar ribose.

• The four bases found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).

• RNA contains the same bases, except that Uracil (U) replaces thymine.

• Adenine and Guanine are purines and are two ringed structures.

• Others are single ringed and are called pyrimidines.

• These structures constitute the alphabet of genetics. Ribose contains a hydroxyl (OH) group in the 2 - position. Deoxyribose lacks the oxygen and simply has a hydrogen.

• The bases and sugars in RNA and DNA are joined together into units called Nucleosides.
• The subunits of DNA and RNA are nucleotides, which are nucleosides with a phosphate group attached through a phosphodiester bond.