Rough endoplasmic reticulum and polysomes

This electron micrograph shows a cell with RER and many polysomes, or polyribosomes.  Polysomes are groups of ribosomes attached to a single messenger RNA molecule that synthesize protein for internal use by the cell.  30,000x

Each polyribosome contains a single mRNA molecule being translated by many ribosomes.  For some proteins, e.g., cytoskeletal and metabolic proteins, translation occurs in the cytoplasm.  For others, such as secreted proteins or membrane spanning proteins, translation is temporarily halted while the polyribosome is translocated to the ER where translation continues.  The signal for where translation occurs is contained in the leader sequence of the mRNA.

This electron micrograph shows a cell with RER and many polysomes, or polyribosomes.  Polysomes are groups of ribosomes attached to a single messenger RNA molecule that synthesize protein for internal use by the cell.  30,000x

This electron micrograph shows a cell with RER and many polysomes, or polyribosomes.  Polysomes are groups of ribosomes attached to a single messenger RNA molecule that synthesize protein for internal use by the cell.  30,000x

This electron micrograph shows a cell with RER and many polysomes, or polyribosomes.  Polysomes are groups of ribosomes attached to a single messenger RNA molecule that synthesize protein for internal use by the cell.  30,000x