Protein synthesis - polysomes

The protein synthesis as shown before is in fact simultaneously performed on a series of ribosomes all using in succession the same mRNA template. This complex is called a polysome and is seen on the animation below.

mRNA which carries information about the sequence of the aminoacids in the future protein chain fuses with ribosome subunits on the surface of the endoplasmic reticulum (ER). Many ribosomes work using the code of a single mRNA. Such assemblies are called polysomes. The aminoacids of which protein is composed are brought by the tRNA molecules

The growing protein chain protrudes into the lumen of the endoplasmic reticulum.