ENDOPLASMIC RETICULUM (ER)
The nuclear membrane links with the membrane of the endoplasmic reticulum (ER). It is a system of complex network scattered throughout the cell. Present in Eukaryotic cells & are of two types: Rough endoplasmic reticulum (RER) & Smooth Endoplasmic reticulum (SER).
ROUGH ENDOPLASMIC RETICULUM
Ribosomes are attached on the surface of endoplasmic reticulum and it appears granular hence known as Rough Endoplasmic reticulum .
FUNCTION RER
The main function of RER is to keep together and transport the proteins made on the ribosomes.
Instead of simply diffusing away into the cytoplasm, newly made proteins enter into RER. Here they fold into three-dimensional shape.
A mature cell that makes and secretes large amounts of protein – such as one that makes digestive enzymes – has RER that occupies as much as 90 per cent of the total volume of the cytoplasm.
RER is also a storage unit for enzymes and other proteins. Small vesicles containing newly synthesized proteins pinch off from (he ends of the RER
and either fuse with the Golgi complex or pass directly to the cell surface membrane.
SMOOTH ENDOPLASMIC RETICULUM
ER with no ribosomes attached is known as SER.Smooth ER is not involved in protein synthesis but is the site of steroid (lipid hormone) production.
Functions of SER
It also contains enzymes that detoxify, or make harmless, a wide variety of organic molecules, and it acts as a storage site for calcium in skeletal muscle cells.
The channels having material present in them which is separated from the cytoplasmicmaterials by the spherical or tubular membranes is called cisternae.
E.R provides mechanical support to the cell.
In some cells SER transmit impulses. For example nerve and muscle cells.
Both RER and SER are involved in the transportation of materials from one part of the cell to the other.