The endoplasmic reticulum (ER) is a network of membrane-bound sacs and tubules that extends throughout the cytoplasm. It was first observed in 1945 and named ER in 1953. The ER is present in most eukaryotic cells except mature red blood cells. It has three types of structures - cisternae, tubules, and vesicles. The ER membrane is continuous with the nuclear membrane and Golgi complex. There are two types - smooth ER lacking ribosomes, found near the cell membrane, and rough ER with ribosomes on its surface, found deeper in the cytoplasm and involved in protein synthesis. The ER functions include intracellular support, transport, increased surface area for enzymes, and synthesis of proteins,

1. ENDOPLASMIC RETICULUM (ER)
Dr. Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry

2. ENDOPLASMIC RETICULUM (ER)
• Cytoplasmic matrix is traversed by a complex
network of inter – connecting membrane
bound vacuoles or cavities, remain
concentrated in the endoplasmic portion of
the cytoplasm – hence the name ER.
• First noted by Porter, Claude and Fullman
(1945).
• Named ER by Porter (1953).

3. • Present in almost all
eukaryotic cells except
ova, embryonic cells
and mature RBCs.
• ER seen in striated
muscle cells –
‘Sarcoplasmic
reticulum’ (SR).

4. ER -Transmission electron micrograph

5. Morphology of ER :
Three kinds of structures
a) Cisternae – flattened ,
unbranched sac- like
structures arranged in
parallel stacks –
Diameter 4 to 50 mµ.
Bear ribosomes on the
surface.

6. b) Tubules
• Irregular, branched –
form a network along
with other elements.
• Diameter 50 to 190
mµ
• Free of Ribosomes

7. c) Vesicles
• Oval or round , vacuole – like
elements.
• Occur isolated in the cytoplasm.
• Free of Ribosomes.

8. Ultrastructure of ER :
• The cavities of Cisternae, Vesicles and
Tubules are bound by a membrane of 50 – 60
A° thickness.
• The membrane is trilaminar, composed of an
outer and inner dense layers of protein
sandwiching two layers of phospholipids.
• The membrane of ER remain continuous with
the plasma membrane, nuclear membrane
and Golgi complex.

9. Types Of ER :
a) Smooth (Agranular) ER
[ SER]
• Devoid of Ribosomes
• Forms a tubular
network
• Usually lies near the cell
membrane
• Well developed in
muscle cells, adipose
tissue cells, glycogen
storing liver cells etc.
SER - Transmission electron micrograph

10. Types Of ER :
b) Rough (Granular) ER
[ RER]
• Has Ribosomes attached
to its outer surface –
makes the surface rough
or granular.
• Found abundantly in
cells which are active in
protein synthesis –
Pancreatic cells, liver
cells. The region of
cytoplasm containing
RER takes basophilic
stain- ‘Ergastoplasm’.
RER - Transmission electron micrograph

11. RER
• Consists mainly of
Cisternae
• Ribosomes are present on
its surface
• Usually lies deep in the
cytoplasm
• Take part in the synthesis
of protein
• Arises from the nuclear
envelope by outfolding.
• Gives rise to SER.
SER
• Consists mainly of Tubules
and Vesicles.
• Ribosomes are absent on
the surface
• Usually lies near the cell
membrane.
• Take part in the synthesis
of lipids, steroids, glycogen.
• Arises from the RER by the
detachment of Ribosomes.
• Gives rise to Golgi
apparatus, Lysosomes and
Vacuoles.

12. Functions of ER
1) ER forms an intracellular skeletal frame
work to the cell and gives mechanical
support to the colloidal cytoplasmic matrix.
2) It facilitates transport of materials from one
part of the cell to another.
3) It provides increased surface area for enzyme
activity.
4) ER form new nuclear envelope after each
nuclear division.

13. 5)RER offers extensive surface for protein
synthesis
6) SER provides surface for the synthesis of
cholesterol, lipids, steroid hormones,
glycogen etc.
7) SER produces Golgi apparatus, Lysosomes
and Vacuoles.

14. THANK YOU