How genes direct the production of polypeptides
Gene expression is the process by which a gene product (RNA or polypeptide) is made. Two steps (transcription and translation) are required to make a polypeptide from the instructions in a DNA gene.
In transcription, an enzyme called RNA polymerase makes a copy of one of the DNA strands (an RNA copy).
In translation, this RNA (messenger RNA or mRNA) carries the genetic instructions to the cell’s protein factories called ribosomes. The ribosomes “read” the genetic code in the mRNA and put together a protein according to its instructions.
Ribosomes already contain molecules of RNA (ribosomal RNA or rRNA). Experience shows that ribosomes are non-specific translation machines that can make an unlimited number of different proteins, according to the instructions in the mRNAs that visit the ribosomes.