both molecules contain a phosphate molecule, a pentose sugar and organic bases. dna has a phosphate molecule, pentose sugar which is deoxyribose and the organic bases are adenine, thymine, guanine and cytosine. rna has a pentose sugar which is ribose, has a phosphate molecule and organic bases which are adenine, guanine, cytosine and uracil. rna is a single, short polynucleotide; dna is made of two long polynucleotide chains joined by hydrogen bonds.