Which part of the eukaryotic cell is responsible for modifying and packaging proteins?

The Golgi apparatus is the part of the eukaryotic cell that is specifically responsible for modifying and packaging proteins. Once proteins are synthesized by ribosomes, they are transported to the Golgi apparatus, where they undergo further processing. This may include the addition of carbohydrate groups (glycosylation) or the cleavage of certain segments. After processing, the Golgi apparatus packages these modified proteins into vesicles, which can then be sent to various destinations within the cell or secreted outside the cell.

While ribosomes are crucial for protein synthesis, they do not modify or package proteins. The nucleus plays a key role in storing genetic information and overseeing the process of transcription, but it is not involved in protein modification or packaging. Mitochondria are primarily responsible for energy production through cellular respiration, not for processing proteins. Therefore, the Golgi apparatus stands out as the cell's central hub for protein modification and packaging, which is why it is the correct answer.