* RNA (Ribonucleic Acid) plays a crucial role in protein synthesis. It acts as a messenger, carrying the genetic code from DNA in the nucleus to the ribosomes in the cytoplasm, where proteins are made.

Let's look at the other options:

* DNA (Deoxyribonucleic Acid) is the blueprint of life, containing the genetic instructions for an organism. It resides in the nucleus and is not directly involved in directing protein synthesis.

* Mitochondria are organelles responsible for energy production within cells. They have their own DNA but don't dictate the synthesis of proteins from the cell's primary DNA.

* Ribosomes are the cellular machinery that translate the instructions carried by RNA into proteins. They don't contain the information themselves, but they are the sites where the information is used.

In summary: RNA is the intermediary that carries the instructions from DNA to the ribosomes, directing the process of protein synthesis.