Predominant structure [edit]. DNA is a double-stranded molecule with a long chain of nucleotides while RNA is single-stranded molecule, in most of its biological roles and has a shorter chain of nucleotides (after transcription and splicing, only exons remain in RNA).redominant structure [edit]. DNA is a double-stranded molecule with a long chain of nucleotides while RNA is single-stranded molecule, in most of its biological roles and has a shorter chain of nucleotides (after transcription and splicing, only exons remain in RNA).