Rough Endoplasmic Reticulum: Definition, Types, Structure and Functions

It is a large organelle composed of sheets and membranous tubules that begin near the nucleus and extend through the cell.

The entire structure can represent a large proportion of the endomembrane system of the cell. The endoplasmic reticulum can represent more than 50% of the total lipid bilayer of the cell.

There are two types of endoplasmic reticulum: rough endoplasmic reticulum and smooth endoplasmic reticulum.

Reticulo endoplasmatico rugoso

The rough endoplasmic reticulum is a part of the endomembrane system of the cell and a subset of the endoplasmic reticulum.

This extensive organelle, composed of very twisted but flat sealed sacs, is mainly related to the synthesis, folding, and modification of proteins, especially those that need to be delivered to different organelles within the cell or secreted from the cell.

The rough endoplasmic reticulum is also involved in the cell’s response to unfolded proteins and plays a role in inducing apoptosis due to its close interaction with mitochondria.

It is called the “rough” endoplasmic reticulum because it is characterized by ribosomes on the outer surface that give it a distinctive appearance under the microscope. These ribosomes look like nails and distinguish the organelle from the smooth sections of the endoplasmic reticulum.


Chains of ribosomes, called polysomes, also synthesize some proteins.

The rough endoplasmic reticulum can also be identified by its morphology: it often consists of crushed and convoluted sac-like structures near the nucleus. The lumen of the rough endoplasmic reticulum is continuous with the perinuclear space and the reticulum membranes.

Structure of the Rough Endoplasmic Reticulum

The endoplasmic reticulum can be morphologically divided into two structures: cisterns and laminae. The rough endoplasmic reticulum is composed primarily of laminae, a two-dimensional matrix of flattened sacs that run the length of the cytoplasm.

In addition to ribosomes, these membranes contain an essential protein complex called translocon, which is necessary to translate proteins within the rough endoplasmic reticulum.

The structure of the rough endoplasmic reticulum is also closely related to the presence of elements of the cytoskeleton, especially microtubules.

The reticulum network collapses and reforms only after the cytoskeleton is restored when the microtubule structure is temporarily disrupted.

Changes in the microtubule polymerization pattern are also reflected in changes to endoplasmic reticulum morphology. Furthermore, when ribosomes detach from sheets of rough endoplasmic reticulum, these structures can disperse and form tubular cisterns.

The edges of ER sheets have a high curvature that needs to be stabilized. Proteins called reticulons and DP1 / Yop1p play an essential role in this stabilization. These proteins are integral membrane proteins that form oligomers to form the lipid bilayer.

In addition, they also use a structural motif that is inserted into a membrane leaflet and increases its curvature. These two classes of proteins are redundant since the overexpression of one protein appears to compensate for the lack of the other protein.

Functions of the rough endoplasmic reticulum

The rough endoplasmic reticulum performs several functions within the cell, primarily associated with protein synthesis.

Polypeptides are synthesized, modified, folded into their correct 3-D shape, sorted into an organelle, or marked for secretion. It also plays a vital role in modulating the response of cells to stress and in quality control for the correct folding of proteins.

When the number of unfolded proteins increases, cells change the ratio of tubules: to sheets. This could arise from the most significant area available within the sheets of the rough ER to rescue the unfolded protein, or it could reflect the need for a different proteome of the rough endoplasmic reticulum.

The rough endoplasmic reticulum proteome reflects its specific role within the cell. It contains enzymes involved in RNA metabolism that bind and modify RNA. This is necessary since the organelle is involved in the translation of RNA to protein.

It also contains proteins that recognize various signal sequences within a growing polypeptide and aid in its translocation.

Glycosylation enzymes and proteins that act as molecular chaperones that ensure proper folding of the synthesized polypeptides are also essential proteins within this organelle.

Occasionally, apoptosis is induced by the endoplasmic reticulum in response to an excess of unfolded protein within the cell. This function is consort-mediated with mitochondria.