Which cell structure is responsible for modifying, packaging, and distributing proteins?

The Golgi apparatus is critical for the processing and distribution of proteins within the cell. It acts as a sorting facility, where proteins synthesized in the endoplasmic reticulum are sent for modification. These modifications can include the addition of carbohydrate or lipid groups, which can be important for the protein's function or to determine its final destination within or outside the cell.

Once the proteins are properly modified, the Golgi apparatus packages them into vesicles. These vesicles then transport the proteins to specific locations, such as the plasma membrane for secretion or other organelles for various functions. This organelle's role is essential for ensuring that proteins reach their correct destinations and perform their designated tasks effectively.

Other cell structures mentioned have different primary functions: mitochondria produce energy for cellular processes, lysosomes are involved in digestion and waste removal, and the endoplasmic reticulum is primarily responsible for protein and lipid synthesis but does not modify and package them as extensively as the Golgi apparatus does. Thus, the Golgi apparatus is the key structure involved in the post-translational modification, packaging, and distribution of proteins.