Endoplasmic reticulum

Structure:

• single membrane-bounded

• highly folded in to flattened sacs and tubes which is
  

----cisternae

system of channel extends throughout cytoplasm, from outer nuclear membrane to cell
membrane. It is an extension of the outer nuclear membrane without pore. It filled with fluid containing enzymes for metabolic activities.
Tubular cisternae continuously pinched off to form Golgi Apparatus.

	Rough ER	Smooth ER
Appearance	ribosome attached	no
cisternae	nothing special	more tubular
function	Synthesize protein(secretary,membrane)	synthesize lipid and steroids

Function of all ER:

1. Extensive membrane system acts as cytoskeleton for support
2. Intricate channel of ER facilitate transport .
3. ER membrane provide a large surface area for attachment of enzyme

Example:
rough ER: pancreatic islet cells
smooth ER:sebaceous gland cells