The Postal Service of the Cell

The Golgi Appartus can be described as the post office of the cell.

It packages, labels, inspects, and perfects proteins and other molecules.

Many of the molecules that reach the Golgi will be exported out of the cell and they need to know where they are going. Therefore the Golgi attaches molecular labels to them.

Also the Golgi has a system of postal workers, called vesicles, that will pick up packages from the endoplasmic reticulum (ER) and take them to the edge of the cell membrane after the Golgi's work is done.

As with many other organelles the Golgi alters from cell to cell.

In many cells there is a single Golgi situated to one side of the nucleus. Some other cells have several Golgi apparati appearing as stacks of membranes distributed throughout the cell.

The Golgi is most highly developed in cells which are specialised for secretion such as enzyme releasing cells of the digestive tract.

The Golgi apparatus has three important roles:

• modification of complex molecules (such as proteins) by the addition of sugars.
• proteolysis of peptide molecules which makes them become active.
• sorting of molecules for either, transport out of the cell, incorporation in the cell membrane, or transport to another part of the cell.

To facilitate this the Golgi itself is divided into three functionally separate areas.

1. The cis face (closest to the nucleus and the ER) receives transport vesicles from the smooth ER.
2. The medial Golgi which adds sugars to both lipids (fats) and peptides (proteins).
3. The trans Golgi network (closest to the cell membrane) which performs proteolysis and sorts molecules for their destination.

In this diagram the cis face is seen at the bottom next to the ER and the trans Golgi network is at the top of the picture. Vesicles containing complex molecules are seen breaking away fron the top of the trans Golgi network to be transported out of the cell by exocytosis.

Not all human cells are involved in producing secretions but even in those cells the Golgi has an impotant role in packaging digestive enzymes for intracellular use in the form of lysosomes.

                                                                      Electron micrograph of a section through a Golgi apparatus.

This page last updated on Tue Aug 17 14:41:55 BST 2004

[Back] [Up] [Next]