Question

explain the sequence of movements of a protein that is going to be secreted through the organelles of a cell.

Answer 1

Secretory pathway :

The secretory pathway :

• Newly synthesized proteins enter the biosynthetic secretory pathway in the ER by crossing the ER membrane from the cytosol
• Transfer from one compartment to the next involves a delicate balance between forward and backward transport pathways
• To initiate their journey along the biosynthetic-secretory pathway, proteins that have entered the ER and are destined for the Golgi apparatus or beyond are first packaged into small COPII-coated transport vesicles. These transport vesicles bud from specialized regions of the ER called ER exit sites, whose membrane lacks bound ribosomes
• Some cargo proteins are actively recruited into vescicles and they display transport signals that recognize receptor proteins and then transport the proteins to their target

Now how are the proteins secreted outside the cells:

1. The secretory vescicles containing secretory proteins are released from the trans Golgi network and by detecting the signal, are fused to the membrane where the contents are released. This signals include neurotransmitters or hormona signals. This pathway is called Regulated secretory pathway
2. In a newly synthesized plasma membrane protein, the soluble proteins and lipids are present that fuses with the extracellular membrane in an unregulated manner and releases the proteins to the outer membrane space outside the cell. This pathway is called Constitutive Secretory pathway