Final answer:
mRNA is synthesized by RNA polymerase, which creates a messenger molecule used for protein synthesis. Other types of RNA like rRNA and tRNA play different roles in protein synthesis.
Step-by-step explanation:
mRNA is synthesized by RNA polymerase. This molecule attaches to the DNA during transcription and creates an mRNA molecule, which is a messenger molecule that carries the code for protein synthesis. Neither rRNA, tRNA, nor any of the other options listed are responsible for the synthesis of mRNA. rRNA is a component of the ribosome, which is the site of protein synthesis, and tRNA carries amino acids to the ribosome to be added to the growing protein chain. It is RNA polymerase that traverses the length of a gene and synthesizes the mRNA strand.