I have recently started looking back at the function of the Golgi complex and am now aware not all proteins pass through the Golgi Complex (cytoplasmic translation). However I was always under the impression that most post-translational modifications (PTM) happen in the ER (co-translational) or Golgi complex.

Additionally, some types of PTMs happen in the mitochondria or at other organelles (transmembrane receptors come to mind).

My question is fourfold:

1. Are there specific PTM's exclusive to the Golgi complex.

2. By what mechanism can proteins translated by cytosolic (floating) ribosomes be folded and modified (in the ER the concentration/location of chaperone proteins and PTM-proteins will be much higher, but I can't imagine how that works for cytosolic ribosomes).

3. Are (some) proteins translated by cytosolic ribsomes still transported to the Golgi?

4. In case cytosolic ribosomes and ER ribosomes produce different (types) of proteins, how do they know which mRNA's to translate, or how does the mRNA reach the right ribosomes (escape the ER in case of cytosolic ribosomes)?

Thank you very much,

Jelle Bonthuis