During transcription, RNA polymerase makes a copy of a gene from the DNA to mRNA as needed. This process is similar in eukaryotes and prokaryotes. One notable difference, however, is that prokaryotic RNA polymerase associates with mRNA processing enzymes during transcription so that processing can proceed quickly after the start of transcription. The short-lived, unprocessed or partially processed, product is termed pre-mRNA; once completely processed, it is termed mature mRNA.
Messenger ribonucleic acid, commonly called messenger RNA or mRNA, is an RNA molecule that encodes a chemical "blueprint" for the synthesis of a protein. Messenger RNA contains a copy of the genetic data contained on a strand of DNA. Ribosomal ribonucleic acid (ribosomal RNA or rRNA) helps to form the ribosome itself.
Same like messenger RNA (mRNA), ribosomal RNA does not transmit genetic information. Instead of this it combines with proteins to create a structure that systematically transforms mRNA into proteins.

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