Final answer:
The statement is false; transmembrane domains are inserted into the ER membrane via the translocon and do not fold within it. Ribosomes synthesize proteins that then enter the RER for modifications before being sent to the Golgi apparatus.
Step-by-step explanation:
The statement that transmembrane domains fold up in the translocon during import into the ER is false. Transmembrane domains of integral proteins are inserted into the ER membrane as they are being synthesized by ribosomes. These proteins do not fold within the translocon; instead, they pass through it and anchor in the membrane due to hydrophobic interactions facilitated by stop-transfer sequences. The ribosomes attached to the ER synthesize proteins, some of which will become integral membrane proteins with one or multiple transmembrane domains. These proteins are inserted into the ER membrane and then may undergo further modifications, such as folding, addition of sugars, or acquisition of side chains in the lumen of the Rough ER (RER). Afterward, they are packaged into transport vesicles and sent to the Golgi apparatus for further processing and sorting before reaching their final destination in the cell.