Which of the following cell organelles is responsible for packaging and modifying proteins?

The Golgi apparatus is the organelle responsible for packaging and modifying proteins. It acts as a key processing center within the cell where proteins synthesized in the endoplasmic reticulum are further modified, sorted, and packaged into vesicles for transport to their final destinations. This includes processing such as glycosylation, where carbohydrates are added to proteins, which is crucial for their function and stability.

In contrast, the endoplasmic reticulum is primarily involved in the synthesis of proteins (rough ER) and lipids (smooth ER), but it does not modify or package them for transport. Ribosomes are the sites of protein synthesis, translating mRNA into polypeptide chains, but they lack the capability to modify or package proteins. Mitochondria are primarily involved in energy production through ATP synthesis and do not play a direct role in protein processing or packaging. Therefore, the Golgi apparatus holds a specific and vital function in the post-translational modifications and the distribution of proteins within the cell.