medicinal plants top

Granular (Rough) Endoplasmic Reticulum


Granular (Rough) Endoplasmic Reticulum




The endoplasmic reticulum (ER) is a continuous system of cell membranes,

which are about 6nm thick. Dependent on cell specialization and activity,

the membranes occur in different forms, such as stacks or tubules. The ER

double membranes may be smooth or have granules attached to their outer

surfaces. These granules are about 25nm in diameter and have been identified

as membrane-bound ribosomes. Therefore, two types of ER exist: the granular

or rough form ( rER, rough ER) and the agranular or smooth form (sER,

smooth ER).

Paired multiplanar stacks of lamellae are one characteristic forms of rER. The

membranes are narrowly spaced and spread over large parts of the cell. The

two associated membranes in this matrix are 40–70nmapart. When cells assume

a storage function, these membranes move away from each other and

thus form cisternae, with a lumen that may be several hundred nanometers


Elaborate systems of rER membranes are found predominantly in cells that

biosynthesize proteins. Proteins, which are synthesized

on membranes of the rER, are mostly exported from the cell. They may be secreted

from the cell (including hormones and digestive enzymes, etc.) or

become part of intracellular vesicles (membrane proteins). The smooth endoplasmic

reticulum. eluded light microscopy.

The cisternae of the endoplasmic reticulum interconnect both with the

perinuclear cisternae and the extracellular space.

This picture shows ergastoplasm (rER) from an exocrine pancreas cell, which

produces digestive enzymes.



The granular endoplasmic reticulum (rER) exists not only in the form of

strictly parallel-arranged membrane stacks, which are shown in Figure 21 as

transections. On the contrary, dependent on the specific function of a cell,

rER is found in various forms and dimensions. The transition between granular

and agranular ER can be continuous.

, the rER presents as loosely packed stacks of cisternae with ribosomes

attached to it like pearls on a string (membrane-bound ribosomes). The

figure shows a mitochondrion of crista-type 1 between the rER cisternae.

There are also free ribosomes 3 and polysomes 2 in rosette configuration

present in the cytoplasmic matrix. Such collocations of granular ER cisternae

and adjacent free ribosomes are identical to the structures that are visible

after staining with basophilic dyes in light microscopy preparations