Here's a breakdown:

1. Protein Synthesis: Proteins are synthesized by ribosomes in the cytoplasm.

2. ER Targeting: Some proteins contain a "signal sequence" that directs them to the ER.

3. ER Entry: The ribosome carrying the protein binds to the ER membrane and the protein enters the ER lumen (the space inside the ER).

4. Folding and Modification: Within the ER, proteins undergo folding, glycosylation (addition of sugar molecules), and other modifications.

5. Transport Vesicle Formation: Proteins are packaged into small membrane-bound sacs called transport vesicles.

6. Golgi Transport: These vesicles bud off the ER and travel to the Golgi apparatus.

In summary: Proteins synthesized by ribosomes with an ER signal sequence are transported from the ER to the Golgi apparatus in transport vesicles.