Protein synthesis as shown on a single ribosome

You observe how the protein synthesis occurs on the surface of the endoplasmic reticulum (ER).

How proteins are synthesized

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). 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.