STRUCTURE AND FUNCTIONS

1. ENDOPLASMIC RETICULUM
STRUCTURE AND FUNCTIONS
DR. DILIP V. HANDE
ASSOCIATE PROFESSOR, DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE, AMRAVATI MS.

2. INTRODUCTION
 Endoplasmic reticulum is double membrane
network system observed for the first time by
Porter, Claude & Fullan (1945) in the
cytoplasm.
 Later on in 1953 Porter & Kallmon termed it
as Endoplasmic Reticulum .
 It is an finely divided complex vascular
system extending from the outer nuclear
membrane passing through cytoplasm to
plasma-membrane.
 It is a network of cisternae, tubules &
vesicles.

3. Endoplasmic Reticulum - ER
 Network of hollow membrane tubules
 Connects to nuclear envelope & cell
membrane
 Functions in Synthesis of cell products
& Transport
copyright cmassengale 3Two kinds of ER ---ROUGH & SMOOTH

4. Rough Endoplasmic Reticulum
 Ribosomes attached to surface
◦ Manufacture protiens
◦ Not all ribosomes attached to rough ER
 May modify proteins from ribosomes

5. Rough Endoplasmic Reticulum
(Rough ER)
 Has ribosomes on
its surface
 Makes membrane
proteins and
proteins for
EXPORT out of cell
copyright cmassengale 5

6. Rough Endoplasmic Reticulum (Rough
ER)
 Proteins are made
by ribosomes on
ER surface
 They are then
threaded into the
interior of the
Rough ER to be
modified and
transported
copyright cmassengale 6

7. Smooth Endoplasmic Reticulum
 No attached ribosomes
 Has enzymes that help build molecules
◦ Carbohydrates
◦ Lipids

8. Smooth Endoplasmic Reticulum
 Smooth ER lacks
ribosomes on its
surface
 Is attached to the
ends of rough ER
 Makes cell products
that are USED
INSIDE the cell
copyright cmassengale 8

9. Functions of the Smooth ER
 Makes membrane
lipids (steroids)
 Regulates calcium
(muscle cells)
 Destroys toxic
substances (Liver)
copyright cmassengale 9

10. Endomembrane System
copyright cmassengale 10
Includes nuclear membrane connected to ER
connected to cell membrane (transport)

11. STRUCTURE

12. Occurrence
 It is almost found in all Eukaryotic
cells and more distinct in young
meristematic cells, the amount of
E.R. varies from cell to cell.
 It is found more in amount in those
cells which are active for protein
synthesis.

14. Types
Smooth or Agranular E.R. (SER):-
 The membrane of smooth E.R. are not granular
due to absence of ribosomes .
 It is more abundant near the peripheral part of
the cytoplasm & may found attached to the
plasma-membrane.
 It forms the transport vesicles in which large
molecules (protein & lipid) are transported from
one cell to other through plasmodesmata.
 Rough or granular E.R.(RER )
 The rough E.R. has granular surface due to the
presence of large number of ribosomes attached
to it.
 These are found more abundant in deeper part of
cytoplasm near the nucleus where it is connected
to outer nuclear membrane. It is active protein
synthesis.

16. Structure :
 Morphologically the E.R. consist of three
types of structures. i.e. cisternae. vesicles
and tubules.
 Cisternae :
 The cisternae are elongated, cylindrical,
unbranched flattened sac like lie parallel
to each other.
 These are interconnected with each other
and 40-50 A0 diameter.
 Generally they bears ribosomes on their
cytoplasmic faces and found in cell active
in protein synthesis.

17. Endoplasmic Reticulum
17

18. STRUCTURE
 Tubules :
 These are tube like extension generally connected to
cisternae.
 These are smooth and free from ribosomes.
 The tubules are irregular branching elements
which form network.
 It is having 50- 500 A0 diameter and active in
synthesis of steroid, cholesterol, glycerides.
 Vesicles :
 These are sac like or oval bodies, occur freely in the
cytoplasmic matrix.
 These are also lacking ribosomes. The diameter is
about 25-50 A0

21. Cell Parts and Functions
Endoplasmic Reticulum (E.R.)
Transports materials and sends messages to
all parts of the cell
Two types: smooth and rough (has
ribosomes)
Location: attaches from cell membrane to
nuclear membrane
Rough E.R.

22. STRUCTURE
 E.R. membrane :- The membrane is lipo-
proteinous in nature which encloses the
matrix of E.R.
 It is 50-60 A0 in thickness.
 Various enzymes are associated with E.R.
are stearases, NADH- cytochrome. C-
reductase, Mg++ activated ATPase & other
enzymes like of glycerides, fatty acids, L-
ascorbic acid and steroid metabolism.

23. Endoplasmic Reticulum
 Structure: a system of membranous tubules
and sacs
 Function: intercellular highway (a path along
which molecules move from one part of the cell
to another)
 Two types:
◦ Rough Endoplasmic Reticulum
◦ Smooth Endoplasmic Reticulum

24. Rough Endoplasmic Reticulum
 Rough Endoplasmic
Reticulum (rER):
prominent in cells that
make large amounts of
proteins to be exported
from the cell or inserted
into the cell membrane
◦ Covered with ribosomes

25. Smooth Endoplasmic Reticulum
 Smooth Endoplasmic
Reticulum (sER):
involved in the synthesis
of lipids and breakdown
of toxic substances
◦ Not covered with
ribosomes

26. Functions :
 The network of E.R. separates cytoplasm into
several small compartments which helps the
cell to perform specific activities by providing
enzymes and metabolites within specific
chambers excluding others.
 E.R. given mechanical support to cytoplasm
to provides a kind of inter cellular
cytoskeleton to maintain the form of cell and
keeps cell organelles distributed properly in
relation to one another.
 E.R. has osmotic properties and it is involved
in intra- cellular exchange of materials
particularly between the cytoplasm and the
nucleus.
 E.R. helps in membrane formation in
eukaryotic cell. It play a role in synthesis of
new nuclear membrane using cell division.

27. Functions :
 E.R. serves as circular system for the
transportation of cellular molecules and helps
in the storage of synthesized molecules.
 The enzymes of smooth E.R. involve in the
synthesis of cholesterol their conversion into
the steroid hormone.
 Rough E.R. play a role in protein synthesis
and some specific proteins synthesized by
ribosome when enter into E.R. lumen and
they get modified.
 Some enzymes of E.R. e.g. cytochrome P
450 convert lipid soluble molecules of drugs
into the water soluble molecules.

28. THANKS