Why do ribosomes move along mRNA during translation?
During translation the ribosome always exposes two mRNA codons to be translated by moving along the mRNA. When a peptide bond is made the ribosome moves to expose the next codon. This moving is known as ribosomal translocation. (In the rough endoplasmic reticulum ribosomes are attached outside the membrane and mRNA molecules rather moving by them).
Protein Synthesis - Image Diversity: ribosomal translocation