Final answer:
True, proteins destined for the ER and Golgi must first pass through the ER, where they are synthesized and undergo initial modifications before being transported to the Golgi apparatus for further processing and sorting to their final destinations.
Step-by-step explanation:
The statement that proteins destined to go to the ER and the Golgi to be directed to the appropriate destinations must first move through the ER only is true. The rough endoplasmic reticulum (RER) plays a crucial role in the synthesis of membrane and secretory proteins. Once synthesized, these proteins undergo modifications such as folding or the addition of side chains. If not destined to remain in the RER, these proteins are shuttled by transport vesicles to the Golgi apparatus.
At the Golgi apparatus, proteins continue to undergo processing, including glycosylation and phosphorylation which modify them and often add signal sequences that determine their final destinations. These packaged proteins are then sorted as they move from the cis to the trans face of the Golgi, and from there, they are dispatched to various cellular locations, including the plasma membrane or lysosomes, via vesicles that bud off from the trans-Golgi network.