Golgi apparatus

What is the golgi apparatus?

• Made up of cisternae and sheets

• Generates vesicles

• Modifies and packages proteins and lipids for exocytosis

What is the Cis Golgi Network?

Closest to the endoplasmic reticulum and is the site at which vesicles from the ER dock.

What is the golgi apparatus?

• Made up of cisternae and sheets

• Generates vesicles

• Modifies and packages proteins and lipids for exocytosis

What is the Cis Golgi Network?

Closest to the endoplasmic reticulum and is the site at which vesicles from the ER dock.

What is the Trans Golgi Network?

The site from which vesicles depart for the cell surface or rotherham compartments.

What are the functions of the Golgi apparatus?

Proteins destined for secretion and for a variety of organelles/vesicles within the cell are sorted, modified and dispatched from the Golgi apparatus.

It is also a major site of carbohydrate synthesis in the form of glycoproteins and proteoglycans.

Therefore the Golgi tends to be prominent in secretory cells.

How are proteins dispatched from the endoplasmic reticulum to the golgi?

Almost all proteins in the ER lumen are glycosylated and this acts as a folding tag.

During the initial phases of folding 2 of the 3 terminal glucose molecules are removed.

Calnexin is a chaperone which recognises the single glucose of incompletely folded proteins and prevents their export to Golgi.

The final glucose is removed then:

1. If partially folded glucosyl transferase adds another glucose and it tries again

2. Misfolded proteins are chaperoned back to the ER protein translocator and are sent to the cytoplasm for degradation

3. Correctly folded proteins go on to be exported to the Golgi

How are full folded proteins targeted to ER exit sites?

For soluble proteins this involves interactions with transmembrane receptors.

• Proteins need “exit” signals for efficient export: non-cargos are packaged at a much lower rate

• Most exit signals are not known but:

ERGIC53 receptor protein binds to mannose on Factors V and VIII

ERGIC53 deletion → haemophilia (factor V and VIII involved in blood clotting)

• The coat protein COPII interacts with the cytosolic tail of the receptor causing a vesicle to bud off