Endoplasmic Reticulum

    Electron microscopic studies of eukaryotic cells reveal the presence of a network of reticulum of tiny tubular structures scattered in the cytoplasm that is called the endoplasmic reticulum (ER) 

Components of E.R. :

(1) Cisternae. These are long flattened and unbranched units arranged in stacks.

(2) Vesicles - These are oval membrane bound structures.

(3) Tubules - These are irregular, often branched tubes bounded by membrane. Tubules may free or associated with cisternae.

• Structure of E.R. is like the golgi body but in E.R. cisternae, vesicles and tubules are isolated in cytoplasm and these do not form complex.
• Golgi body is localised cell organelle while ER is widespread in cytoplasm. Er is often termed as "System of Membranes''.

• ER divide the intracellular space into two distinct compartment i.e., Luminal (inside ER) and extra luminal (cytoplasm) compartments.

fig : E.R.

Modifications of E.R.(Endoplasmic Reticulum) :

(1)  Sarcoplasmic Reticulum (S.R.) :- These smooth E.R. occurs in skeletal and cardiac muscles. S.R. Stores Ca+2 and energy rich compounds required for muscle contraction.

(2)   Microsomes - These are pieces of ER with associated ribosomal particles. These can be obtained by fragmentation and high speed centrifugation of cell. They do not exist as such in the living cell. Scientist used microsome for invitro protein synthesis study.

FUNCTIONS OF E.R.(Endoplasmic Reticulum) :

(1) Mechanical support :- Microfilaments, Microtubules and E.R. forms endoskeleton of cell

(2) Intracellular exchange :-E.R. forms intracellular conducting system. Transport of materials in cytoplasm from one place to another may occurs through the E.R.

• At some places E.R. is also connected to P.M. Sober can secrete the materials outside the cell.

(3) Rough E.R. :- Provides site for the protein synthesis, because rough E.R., has ribosomes on its surface.

(4) Lipid Synthesis:-Lipids (cholesterol & phospholipids) synthesized by the agranular portion of E.R. (Smooth E.R.).

(5) ER also helps in the synthesis of lipoproteins and glycogen.

(6) Cellular metabolism ;- The membranes of the reticulum provides an increased surface for metabolic activities within the cytoplasm. 

(7) Formation of nuclear membrane :-Fragmented (Mainly rough ER )vesicles of disintegrated nuclear membrane and ER elements arranged around the chromosomes to form a new nuclear membrane during cell division.