Explanation

Post-translational modifications are processes that occur after protein synthesis, and they are essential for the functional maturation and regulation of proteins.

These modifications, such as:

• adding carbohydrate groups (glycosylation)
• phosphate groups (phosphorylation),
• predominantly take place in the endoplasmic reticulum (ER) 
• the Golgi apparatus.

The ER is involved in the initial modifications and folding of proteins,

While the Golgi apparatus further processes and sorts proteins for their final destinations.