The Golgi Apparatus

In this cell (from a bat), the Golgi apparatus (boxed in red) is used for the final stages in the synthesis of proteins that are to be secreted from the cell. (Courtesy of Keith R. Porter.)
The Golgi apparatus is a cell structure mainly devoted to processing the proteins synthesized in the endoplasmic reticulum (ER).

The Golgi consists of a stack of membrane-bound cisternae located between the endoplasmic reticulum and the cell surface.

Many different enzymes (proteins) are present in the Golgi to perform its various synthetic activities. So there must be mechanisms All the details are far from worked out, but these are some of the features for which there is considerable experimental evidence.

The Outbound Path

Two mechanisms appear to participate in the migration of proteins from the endoplasmic reticulum through the Golgi apparatus.

Mechanism 1.

Mechanism 2.

In addition to the pinching off and fusing of shuttle vesicles, the cisternae of the Golgi actually migrate themselves; that is, the cis Golgi gradually migrates up the stack becoming a medial and finally a trans Golgi (depicted in the figure with red arrows).

The Inbound Path

The movement of cisternal contents through the stack means that essential processing enzymes are also moving away from their proper site of action.

Using a variety of signals, the Golgi separates the products from the processing enzymes that made them and returns the enzymes back to the endoplasmic reticulum.

This transport is also done by pinching off vesicles, but the inbound vesicles are coated with COPI (coat protein I)

How does a vesicle recognize its correct target?

This involves pairs of complementary integral membrane proteins

v-SNAREs and t-SNAREs bind specifically to each other thanks to the complementary structure of their surface domains.

Binding is followed by fusion of the two membranes.

The Golgi is not a static cell organelle

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6 June 2021