Question

What distinguishes proteins destined for regulated secretion?

A. They have special surface properties that cause them to form aggregates that are packaged into special secretory vesicles.
B. They have a series of amino acids that act as a tag that marks them for packaging into secretory vesicles.
C. They are cleaved from membrane domains in the Golgi apparatus prior to being packed into secretory vesicles.

Answer 1

Proteins that are destined for regulated secretion are marked for entry into the endoplasmic reticulum, modified in the Golgi apparatus, and sorted by specific proteins to be packaged into secretory vesicles for exocytosis.

Step-by-step explanation:

Proteins destined for regulated secretion are usually marked by a signal sequence that targets them to the endoplasmic reticulum (ER) where they are synthesized. Upon entering the ER, they begin the process of post-translational modification, such as core glycosylation. Subsequently, these proteins are transported to the Golgi apparatus via transport vesicles, where they undergo further modifications. Specific sorting proteins within the Golgi apparatus recognize these modified and tagged proteins to allocate them into different secretory vesicles responsible for various destinations, including the plasma membrane for exocytosis.

When the appropriately tagged proteins reach the trans face of the Golgi apparatus, they are packaged into secretory vesicles. Some vesicles deliver their contents to intra-cellular locations, while others are designed for extracellular release. In response to a signal, the secretory vesicles undergo fusion with the plasma membrane, leading to the release of their contents outside the cell.