In the eukaryote cell nucleus RNA can be found dispersed in the nuclear fluid, along with DNA, and as the main constituent of the nucleolus. In cytosol (in eukaryotes or in bacteria) RNA molecules can be found free, as structural constituent of ribosomes (organelles specialized in protein synthesis) or even associated with them in the process of making proteins.
In replication the enzyme DNA polymerase catalyzes the formation of a new polynucleotide chain using free nucleotides in solution and putting them in the new chain according to the DNA template exposed and to the rule A-T, C-G. In transcription the enzyme RNA polymerase makes a new polynucleotides chain according to the DNA template exposed obeying, however, the rule AU, C-G.
In replication the original template DNA a chain is kept bound by hydrogen bonds to the newly formed DNA chain and a new DNA molecule is then created. In transcription the association between the template DNA chain and the newly formed RNA is undone and RNA constituted of only one polynucleotide a chain is liberated.
