The structure that packages protein molecules for transport and secretion is the Golgi apparatus.

Here's how it works:

1. Proteins synthesized in the endoplasmic reticulum (ER) are transported to the Golgi apparatus in transport vesicles.

2. The Golgi apparatus modifies, sorts, and packages these proteins. This includes adding carbohydrates, folding them correctly, and sorting them based on their destination.

3. Proteins are then packaged into different types of vesicles:

* Secretory vesicles transport proteins destined for secretion outside the cell.

* Transport vesicles carry proteins to other organelles within the cell.

* Lysosomes contain enzymes for cellular degradation.

4. Vesicles bud off from the Golgi apparatus and move to their target destinations.

In summary, the Golgi apparatus acts as a central processing and packaging plant for proteins, ensuring that they are properly modified and delivered to the correct location within the cell or outside of it.