Rough endoplasmic reticulum (RER) looks rough under the microscope because of the attachment of which one of the following cell organelles to its surface?

The Rough Endoplasmic Reticulum (RER) derives its name from its physical appearance under an electron microscope, where it appears studded with tiny, granular structures [1]. These structures are ribosomes, which are attached to the cytoplasmic surface of the ER membrane. Ribosomes are the sites of protein synthesis, translating genetic information from mRNA into polypeptide chains [1]. While the Smooth Endoplasmic Reticulum (SER) lacks these attachments and is primarily involved in lipid synthesis and detoxification, the RER specializes in producing proteins destined for secretion or membrane insertion [1]. The attachment of ribosomes to the RER is dynamic; they bind to specific sites called translocons when a signal peptide is recognized during the translation process [1]. Consequently, the presence of these numerous fixed ribosomes gives the RER its characteristic 'rough' or 'studded' texture.

Sources

1. [1] https://www.sciencedirect.com/topics/immunology-and-microbiology/rough-endoplasmic-reticulum