ENDOPLASMIC RETICULUM

The endoplasmic reticulum is a membranous system which is continuous with the outer nuclear membrane and scattered extensively in the cell. It forms an intra cellular transport system and a cytoplasmic skeleton. There are 2 distinct types of ER :

a.       Rough endoplasmic reticulum

The rough endoplasmic reticulum consists of an interconnected system of membrane bound flattened sacs called cisternae. It is continuous with the outer membrane of the nucleus and has many ribosomes on the outer surface of membrane. Rough endoplasmic reticulum is abundant in cell which are rapidly growing or secretory cell.

b.      Smooth endoplasmic reticulum

The smooth endoplasmic reticulum lacks ribosomes and is a system of interconnected tubules. Smooth ER is abundant in cell involved in lipid and steroid hormone synthesis e.x. cells in e testes and ovaries or cells involved in detoxification in liver.

Function of ER

a.       Intracellular transport of protein

Polypeptide chains synthesised by ribosomes are modified e.g. to form glycoprotein and transported in the rough ER. Transport vesicles containing modified protein are budded off from rough ER and are transport to Golgi apparatus.

b.        The smooth ER is the site of lipid synthesis and the metabolism of carbohydrates.

c.       Enzym of the smooth ER in the liver cell are involved in detoxification

d.      The smooth ER become modified to form the sarcoplasmic reticulum surrounding the muscle myofibril. It stores or release calcium iions for muscle contraction.

e.      The endoplasmic reticulum divided the cytoplasm into more compartement and increases surface area for chemical reactions take place.