The major site of protein modification and sorting within a cell is known as?

The major site of protein modification and sorting within a cell is the Golgi apparatus. This organelle functions as a central hub in the secretory pathway, and it is essential for post-translational modifications of proteins, such as glycosylation, phosphorylation, and sulfation.

Once proteins are synthesized in the endoplasmic reticulum, they are transported to the Golgi apparatus, where they undergo further modifications and are sorted for delivery to their final destinations, which could include secretion outside the cell, incorporation into the plasma membrane, or delivery to lysosomes.

The Golgi apparatus comprises a series of flattened membrane-bound sacs called cisternae, and proteins move through these compartments in a highly regulated manner. This sorting process is critical for the proper function of proteins, as distinct modifications and the correct localization are essential for their biological roles.