Question

A protein destined for the extracellular space could be translocated there in which of the following ways?

1) It is impossible to move proteins outside the cell.
2) Use of hydrophilic sequences to move everything properly
3) Type I secretion system
4) Use of SRP to deliver to membrane followed by Sec system to move into periplasm

Answer 1

Proteins destined for extracellular spaces are translocated there through a process involving the endomembrane system, which directs the proteins from the endoplasmic reticulum to the Golgi apparatus, and ultimately to the plasma membrane where they are released outside the cell.

Step-by-step explanation:

A protein destined for the extracellular space could be translocated outside of the cell through a well-orchestrated process involving the endomembrane system. This system includes the rough endoplasmic reticulum (RER), where proteins begin post-translational modification such as glycosylation, and the Golgi apparatus, where they are further modified and sorted to their appropriate destination. Specifically, transport vesicles carry proteins from the RER to the Golgi apparatus, where they are sorted and packaged into new vesicles that travel to and fuse with the plasma membrane, thereby releasing the proteins into the extracellular space. This process aligns with option 4 of the student's question, utilizing the Signal Recognition Particle (SRP) to deliver proteins to the membrane and the Sec system to move proteins into the periplasm and eventually out of the cell.