Here's why:

* DNA in the nucleus contains the genetic code. This code is the blueprint for making proteins.

* mRNA is a copy of a gene from DNA. It's like a messenger taking the instructions from the nucleus to the ribosomes.

* Ribosomes are the protein factories of the cell. They use the information in the mRNA to assemble amino acids into proteins.

So, the journey looks like this:

1. DNA in the nucleus contains the gene for a specific protein.

2. mRNA is created as a copy of that gene.

3. mRNA travels out of the nucleus and into the cytoplasm.

4. mRNA binds to a ribosome.

5. The ribosome reads the mRNA code and assembles amino acids into a protein.

Let me know if you'd like more information about the process of protein synthesis!