Vesicular Transport. Pages 512 - 528. The general flow of membrane enclosed material within cells. The general flow of membrane enclosed material within cells - utilizes the endomembrane system as a system of highways. 15_17_Vesicles_bud.jpg. Vesicular Transport. Question:
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Pages 512 - 528
The general flow of membrane enclosed material within cells - utilizes the endomembrane system as a system of highways15_17_Vesicles_bud.jpg
Answer: use special protein paint to coat each vesicle on cytoplasmic side. Each paint color directs its vesicle along just one pathway
The cell does the same using different combinations of proteins to cover each vesicle.
General Properties of vesicle formation
Best studied system are vesicle coats made of clathrin. These vesicles bud from either the Golgi or the plasma membrane. Interplay of several proteins -
The material itself carries transport signals, that binds to cargo receptors. It appears that there are different kinds of adaptins in different areas
Vesicles travel along the cytoskeleton highway of the cell - more about these in a latter lecture
The SNARE proteins act like bag ties. They twist around each other bringing the two membranes close together until they fuse!15_21_membr_fusion.jpg
Material leaving the ER is stringently checked for quality - a quality control step. Material that fails to pass these tests is held back and eventually degraded. Some material actually carries a ER retention signal and if it is not properly removed the material is returned to the ER from the Golgi!15_23_Chaperones.jpg
The Golgi apparatus is normally located near the nucleus. It consists of a collection of flattered membranous disks. It has orientation - cis face, trans face
The Golgi itself may modify material too!
A classic example of vesicles that excrete material - in this case these cells are pancreatic B cells releasing insulin into bloodstream15_29_Secretory_vesicl.jpg
A macrophage ingesting, via phagocytosis, two RBC. FACT: each day 10E11 RBC are deleted from your body by this process!15_31_macrophage.jpg
The cell gains its cholesterol via specialized receptors. Note that the receptors are recycled to the cell surface!15_32_LDL_enters.jpg
The endomomes are key players in the endocytosis pathway, just as the Golgi was in the exocytosis pathway.
Endosomes determine the eventual outcome for ingested material
There are three possible outcomes from an early endosome:
Not know how lysosomes form: they may convert from an endosome or be made directly from the Golgi