ENDOPLASMIC RETICULUM (ER)

(i) Introduction and Discovery

• The E.R. is another important cell organelle that is present in all eukaryotic plant and animal cells.
• But these are absent in prokaryotic cells.
• The E.R. was first discovered by Garnier in the year 1897.
• The structure of E.R. was described by Porter in the year 1953.
• The term Endoplasmic Reticulum was given by Fullmann in 1953.

(ii) Types of E.R.

• The E.R. is divided in 2 types depending on the presence or absence of ribosome, i.e.

1. Granular E.R. (Rough E.R.)
2. Agranular E.R. (Smooth E.R.)

Smooth Endoplasmic Reticulum                                 Rough Endoplasmic Reticulum

• Ribosomes are not present on the surface.          • Ribosome are present on the surface.
• These are present near the plasma membrane   .•These are mainly present near the nucleus.
• It consists of the tubules.                                       • It consists of cisternae.
•  As ribosomes are absent, it doesn’t help

in the protein synthesis.It helps in lipid synthesis.    Ribosomes are present, it helps protein synthesis .

(iii)Structure of E.R.

• Structurally the E.R. consists of three components:

1. a) Cisternae

• These are flat, elongated structures present in the form of stalk.
• In case of R.E.R., there are about 6 to 8 cisternae present.
• They are present one above another and are interconnected.

1. b) Vesicles                                                                                                                                                                              These are small, rounded structures which are present throughout the cytoplasm.

• These are developed from the cisternae by the process of exocytosis. .
• They may be rough or smooth.

1. c) Tubules

• These are tube like structures having the diameter of 50-100.
• These may be branched or unbranched.
• All the above three structures together constitute the cytoskeleton of endoplasmic reticulum.

(iv) Function of E.R.

• The E.R. acts as the cell circulatory system and it helps in the transport of different materials in a particular path.R.E.R. – S.E.R.- Golgi body Pr. Lysosome ⎯⎯→out of cell.It helps in the compartmentalization of cell.

• It acts as the storage reservoir of different materials.
• It helps in protein synthesis as well as lipid synthesis.
• The E.R. also synthesizes 30 different types of enzymes.
• It also synthesizes the steroid hormones.
• The E.R. also helps in the formation of primary lysosome.                                                                                                                                                                                                    PRESENTED BY                                                                                                                                                    Sarmistha Swain (Lect. in Zoology)