alkali, base - any of various water-soluble compounds capable of turning litmus blue and reacting with an acid to form a salt and water; "bases include oxides and hydroxides of metals and ammonia"

cytosine, C - a base found in DNA and RNA and derived from pyrimidine; pairs with guanine

T, thymine - a base found in DNA (but not in RNA) and derived from pyrimidine; pairs with adenine

organic compound - any compound of carbon and another element or a radical