Here's why:

* DNA is located in the nucleus: The genetic code, which is contained within DNA, must be accessed for transcription to occur.

* mRNA is synthesized in the nucleus: The mRNA molecule, which carries the genetic code from the DNA to the ribosomes for protein synthesis, is created during transcription.

* Nuclear pores allow mRNA to exit: Once transcribed, mRNA molecules must exit the nucleus through specialized pores to reach the ribosomes in the cytoplasm.

Let me know if you'd like to learn more about the process of transcription itself!