Endoplasmic reticulum

The endoplasmic reticulum is a eukaryotic cellular organelle.

Structure of the endoplasmic reticulum

The endoplasmic reticulum is a network of membrane tubules (often interconnected) arranged through the cytoplasm of eukaryotic cells. Its membrane alone makes up more than half of the cell membrane system, and is in contact with the nuclear envelope.

The endoplasmic reticulum may be:

• granular (GER), when it contains ribosomes which form the "granules" ;
• or smooth (SER).

Role of the endoplasmic reticulum

The granular endoplasmic reticulum is firstly the site of synthesis (in its associated ribosomes) of proteins secreted outside of the cell and secondly of proteins and lipids forming the cellular organelle membranes (Golgi apparatus, lysosomes, mitochondria, nucleus, ribosomes, vesicles, etc.). It contributes to the correct foldings of the proteins that have just been synthesised.

The smooth endoplasmic reticulum takes part in cellular metabolism by synthesising lipids and storing calcium.