Why is protein synthesis diffrent in prokaryotes and eukaryotes?

In prokaryotes, translation occurs in the cytoplasm, where the large and small subunits of the ribosome bind to the mRNA. In eukaryotes, translation occurs in the cytosol or across the membrane of the endoplasmic reticulum where the entire ribosome/mRNA complex binds to the outer membrane of the rough endoplasmic reticulum and the new protein is synthesized and released into the ER; the newly created polypeptide can be stored inside the ER for future vesicle transport and secretion outside the cell, or immediately secreted.

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