how were the researchers able to independently measure dna synthesis and rna synthesis? how were the researchers able to independently measure dna synthesis and rna synthesis? uridine is a nucleoside building block for both dna and rna, but thymidine is a nucleoside building block for dna only. thymidine is a nucleoside building block for both dna and rna, but uridine is a nucleoside building block for rna only. uridine is a nucleoside building block for dna, but not rna, whereas thymidine is a nucleoside building block for rna, but not dna. thymidine is a nucleoside building block for dna, but not rna, whereas uridine is a nucleoside building block for rna, but not dna.