Here's why:

* DNA in the Nucleus: The nucleus of a cell contains the genetic code (DNA). This code holds the instructions for building and maintaining the cell.

* Transcription: The process of copying the DNA code into mRNA is called transcription. This happens within the nucleus.

* mRNA Travels to the Cytoplasm: mRNA, which is a single-stranded molecule, then leaves the nucleus and travels to the cytoplasm.

* Translation: In the cytoplasm, the mRNA encounters ribosomes, which are the protein-making machinery of the cell. The ribosomes read the mRNA code and use it to assemble amino acids into proteins.

So, mRNA acts as the messenger carrying the genetic blueprint from the nucleus to the cytoplasm where proteins are made.