Final answer:
DNA is the fundamental director of protein synthesis, with mRNA acting as the messenger that carries the genetic code from DNA to the site of protein synthesis at the ribosome.
Step-by-step explanation:
The ultimate director of the entire protein building is DNA. Information flow in an organism follows from DNA to mRNA to protein. DNA, through the process of transcription, dictates the sequence of mRNA, and during translation, RNA dictates the structure of the protein to be synthesized. This is encapsulated in the Central Dogma of Molecular Biology.
mRNA is the messenger molecule that provides the code for protein synthesis, interacting with ribosomes to produce proteins. The rRNA makes up the ribosomes where proteins are synthesized, and the tRNA brings the correct amino acids to the ribosome to be added to the growing protein chain. Therefore, while the immediately active entities in protein synthesis are mRNA, rRNA, and tRNA, it is the DNA that ultimately directs the process by determining the sequence of mRNA and consequently the sequence of amino acids in a protein.