Yes, the endoplasmic reticulum (ER) can have ribosomes associated with it, particularly on its rough ER variant. The rough ER is studded with ribosomes on its cytoplasmic surface, giving it a ‘rough’ appearance under a microscope.
These ribosomes play a crucial role in protein synthesis. As the ribosome translates mRNA into proteins, these proteins are threaded into the lumen of the rough ER where they can undergo folding and modification. This process is essential for the production of proteins that are either secreted from the cell, incorporated into the cell’s plasma membrane, or sent to an organelle.
In contrast, the smooth ER does not have ribosomes attached to it and is involved in lipid synthesis, detoxification, and calcium storage. Thus, the presence or absence of ribosomes is a defining feature that distinguishes rough ER from smooth ER.