ENDOPLASMIC RETICULUM

 ENDOPLASMIC RETICULUM

·    Continuous with the outer membrane of the nuclear envelope is a netlike arrangement of flattened hollow tubules called Endoplasmic Reticulum (ER).

·       It is around 40 to 70 nm in diameter.

·       Many flattened sacs called Cisternae are present in Endoplasmic Reticulum.

·   Two types of Endoplasmic Reticulum are (i) Rough Endoplasmic Reticulum (RER) and (ii) Smooth Endoplasmic Reticulum (SER).

i) Rough Endoplasmic Reticulum

·   Rough Endoplasmic Reticulum (RER) is named for its Rough appearance, which is due to the Ribosomes (site of Protein synthesis) attached to its outer (cytoplasmic) surface.

·     RER lies immediately adjacent to the cell Nucleus, and its membrane is continuous with the outer membrane of the nuclear envelope.

·      Proteins produced by Ribosomes on the RER are inserted into the Lumen (central canal) of the RER and transported throughout the cell.

·    RER is a major producer of Glycoproteins and also produces new membrane material that is transported throughout the cell to enlarge the various membrane systems before cell division.

  ii) Smooth Endoplasmic Reticulum

·    Smooth Endoplasmic Reticulum (SER) is a Tube like membrane and it is not associated with Ribosomes.

·     The SER has a wide range of functions including Synthesis and Transport of Carbohydrates and Lipid.

·  Lipids such as Phospholipids and Cholesterol are necessary for the construction of Cell membranes.

·       SER also synthesizes Fats and Steroids such as Estrogens and Testosterone.