The RNA molecule copy of DNA code for a polypeptide is called messenger RNA (mRNA) because it carries the genetic message from the DNA in the nucleus to the ribosomes in the cytoplasm.

Here's why:

* Messenger: It acts as a messenger molecule, transporting the genetic information from the DNA template to the site of protein synthesis (the ribosomes).

* RNA: It is composed of ribonucleic acid, a single-stranded nucleic acid similar to DNA but with uracil instead of thymine.

* Code for a polypeptide: The sequence of nucleotides in mRNA encodes the amino acid sequence of a specific polypeptide chain.

In essence, mRNA is like a blueprint that instructs the ribosomes how to assemble the amino acids in the correct order to create a specific protein.

Let me know if you have any other questions! 😊