A sequence of three bases on mRNA is called a codon . One codon codes for one amino acid. The enzyme RNA polymerase regulates transcription. There are regions in the pre mRNA that have specific characteristics. Promoter regions indicate the starting point of protein synthesis.
Exons are regions of mRNA that actually codes for the final protein.
They are clipped out before translation takes place. So the mature mRNA contains no introns. At the end of the mRNA is a terminal region which stops protein synthesis. A ribosome is a large protein molecule which helps direct protein synthesis. The region on the tRNA that binds to the codon on the mRNA is called an anticodon .