245 bio vesicular transport

vesicular transport

allows materials to exit or enter cell

exocytosis

Vesicle fused to plasma membran, releasing content to surrounding

Endocytosis

Formation of vesciular structure grab stuff outside to inside; bud inward

Signal transmission between organelles

 mediated by vesicles formed by one organelle which is delivered to another organelle 

formation of clathrin coated pit to a clathrin coated vesicle

1. The cargo receptor in the organelle captures specific cargo (the stuff being transported).

2. Adaptin helps the cargo receptor hold onto the cargo and attaches it to the clathrin.

3. The clathrin proteins form a coat around the pit, shaping the membrane into a budding vesicle.

4. Dynamin pinches off the vesicle from the membrane after budding.

5. The vesicle is fully formed and coated with clathrin.

6. Both clathrin and adaptin are released, leaving a naked transport vesicle ready for delivery.

Key: Cargo receptor + adaptin → clathrin coat → dynamin pinches → coat removed → naked vesicle.

Rab proteins, tethering proteins and SNARES (t)

1. A Rab protein on the vesicle surface interacts with a tethering protein on the target membrane, helping the vesicle recognize and lock onto the correct membrane.

2. The v-SNARE (on the vesicle) binds to the t-SNARE (on the target membrane)

3. Fusion: SNAREs act like a winch, twisting together and pulling the vesicle and membrane close. This helps the lipid bilayers fuse, and the vesicle delivers its contents.

4. Final Step: Once fused, the SNAREs are pried apart to complete the process.

Key: Rab + tether → SNAREs dock and twist → membranes fuse → SNAREs separate.

Receptor-mediated endocytosis

1. Specific macromolecules in the extracellular fluid bind to receptors on the cell surface.

2. These receptor-macromolecule complexes gather into clathrin-coated pits (receptor ligand complex)

3. Clathrin shapes the membrane into a vesicle, which then pinches off and enters the cell.

4. vesicle merges with an endosome, which has a low pH. The acidic environment causes the macromolecule to detach from the receptor.

5. Receptors return to the plasma membrane, while the macromolecule, such as LDL, is sent to the lysosome for breakdown.

   Key: Bind → clathrin vesicle → endosome acid → detach → receptors recycle, LDL to lysosome.