Central Dogma
Information in molecular biology flows from DNA, which is replicated, to RNA by transcription, and then polypeptide sequence by translation. There are exceptions to this such as reverse transcription from RNA to DNA and RNA replication, both are found in some viruses. There is also the replication of prion protein structures. Signals from the environment also constitute a major source of information that influences all of these steps.
This is not to imply that all DNA is transcribed into RNA nor that all RNA is translated into Protein. The majority of DNA in eukaryotic genomes is not transcribed, DNA can have a function in its own right (such as chromosomal structural sequences), and many RNA's carry out their functions without being translated into proteins.
DNA-DNA, DNA-RNA, DNA-Protein, RNA-RNA, RNA-Protein, and Protein-Protein interactions are all necessary mechanisms to carry out these steps of information flow.
