Rough Endoplasmic Reticulum (RER)


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In this transmission electron micrograph, the nucleus is the most prominent feature. The nucleolus is a circular, dark region inside the nucleus. A nuclear pore can be seen in the nuclear envelope that surrounds the nucleus. The rough endoplasmic reticulum surrounds the nucleus, appearing as many layers of membranes. A mitochondrion sits between the layers of the E R membrane.
This transmission electron micrograph shows the rough endoplasmic reticulum and other organelles in a pancreatic cell. (credit: modification of work by Louisa Howard)

OpenStax Biology 2e

Scientists have named the rough endoplasmic reticulum (RER) as such because the ribosomes attached to its cytoplasmic surface give it a studded appearance when viewing it through an electron microscope.

Ribosomes transfer their newly synthesized proteins into the RER’s lumen where they undergo structural modifications, such as folding or acquiring side chains. These modified proteins incorporate into cellular membranes—the ER or the ER’s or other organelles’ membranes. The proteins can also secrete from the cell (such as protein hormones, enzymes). The RER also makes phospholipids for cellular membranes.

– What is a flattened membrane disk of the endoplasmic reticulum and Golgi apparatus?

If the phospholipids or modified proteins are not destined to stay in the RER, they will reach their destinations via transport vesicles that bud from the RER’s membrane.

Since the RER is engaged in modifying proteins (such as enzymes, for example) that secrete from the cell, you would be correct in assuming that the RER is abundant in cells that secrete proteins. This is the case with liver cells, for example.

– The outer face of the rough endoplasmic reticulum is studded with what that are the sites of protein synthesis?

The ER was observed with light microscope by Garnier in 1897, who coined the term ergastoplasm. With electron microscopy, the lacy membranes of the endoplasmic reticulum were first seen in 1969 by Keith R. Porter, Albert Claude, and Ernest F. Fullam. Later, the word reticulum, which means “network”, was applied by Porter in 1953 to describe this fabric of membranes.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: