QUESTION 12: WHERE IS THE RNA?

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Although to answer the question of where the DNA is, we only have to know if we were talking about a eukaryotic cell (with differentiated nucleus) or a prokaryotic cell (without differentiated nucleus), when the question arises for RNA, the answer is complicated. And this is so because there is no single RNA and because the place where it is synthesized and the place where it performs the function that has to fulfill is not always the same.

But, let's start with the simplest case. In prokaryotes, as we have said, there is no nucleus understood as an independent compartment. Therefore, the genetic material is not enclosed in any isolated structure. In this way there is no other possibility than to find the RNA, regardless of the type in question, in the cytoplasm.

In eukaryotes, the situation is more complex. First, we must bear in mind that the synthesis of RNA, whatever the type, is in the nucleus, but the translation of that sequence into a sequence of proteins occurs in the cytoplasm. In addition, both processes (transcription and translation) take place both the maturation of the RNA and its transport to the exterior of the nucleus. Therefore, if we consider that the rRNA and tRNA perform their function in the synthesis of proteins and this takes place in the cytoplasm, it is immediate to conclude that it will be here where we can find them both. On the other hand, the regulatory RNA or RNAs plays an important role in the maturation of the mRNA, and as this is carried out in the nucleus, it will be where we find it. Finally, the mRNA can be found both inside the nucleus and in the cytoplasm. Finding it to a greater or lesser extent inside or outside the nucleus will depend on the half-life of the synthesized mRNA, and this, ultimately, will depend on the maturation process that the molecule has undergone.