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Intracellular vesicular transport: Part I From the er to the Golgi Apparatus

Intracellular vesicular transport: Part I From the er to the Golgi Apparatus. Types of Coated Vesicles. TRANSPORT FROM THE ER THROUGH THE GOLGI APPARATUS. Introduction/Basic Concepts Transport and Modification Many sorting steps for the proteins. Golgi Apparatus

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Intracellular vesicular transport: Part I From the er to the Golgi Apparatus

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  1. Intracellular vesicular transport: Part I From the er to the Golgi Apparatus

  2. Types of Coated Vesicles

  3. TRANSPORT FROM THE ER THROUGH THE GOLGI APPARATUS • Introduction/Basic Concepts • Transport and Modification • Many sorting steps for the proteins. • Golgi Apparatus • Major site for CHO synthesis. • Sorting and dispatching “station” for ER products. • Some of the small CHOs get attached to the proteins and directing their transport.

  4. Degraded by proteosomes

  5. Incompletely formed antibody molecules are retained within the ER

  6. HOW DO ER PROTEINS MOVE TO THE GOLGI APPARATUS? • ER transport vesicles have budded from the ER exit sites (see slide # 13) • Proteins on the vesicle’s surface allow for recognition and fusion. • The fusion forms “vesicular tubular clusters.”

  7. Vesicular Tubular Clusters Mediate Transport from the ER to the Golgi Apparatus Clusters are short-lived and simply function as transport containers and eventually fuse with the cis side of the Golgi Apparatus.

  8. Vesicular Tubular Clusters Mediate Transport from the ER to the Golgi Apparatus RETROGRADE TRANSPORT: Also notice the budding off from the vesicular tubular cluster, returning ER proteins and cargo receptors that participated in the ER budding reaction.

  9. Proteins that “came from” and “belong” to the ER (soluble ER resident proteins) must be returned to the ER. Receptors within the Golgi apparatus recognize and capture these ER proteins. The Golgi apparatus receptor releases the ER protein and is eventually returned to the Golgi apparatus.

  10. The Golgi Apparatus Consists of an Ordered Series of Compartments . . . Flattened, membrane enclosed compartments called cisternae, resembling flattened “stacks of pita bread.”

  11. Animal cell Cis face of the Golgi is always closest to the ER.

  12. Plant cell: Golgi are usually more distinct and separated than animal cells.

  13. Transported Molecules Undergo an Ordered Series of Modifications • CGN or cis Golgi Network • Proteins and lipids enter the cis face. • Proteins entering the cis face can either continue to move onward through the Golgi or be returned to the ER. • TGN or trans Golgi Network • Proteins and lipids will exit from the trans face. • Exiting proteins can end up at the lysosomes, secretory vesicles or the cell surface or be returned to an earlier compartment.

  14. Transported Molecules Undergo an Ordered Series of Modifications • The proteins arrive at the Golgi with a short string of carbohydrates attached, an oligosaccharide. • The Golgi modifies the oligosaccharides into various structures that are common in mature proteins. • After their arrival at the cis face, they move into the middle or medial cisternae and then to the trans cisternae where the addition/modification of the sugars is completed. • The proteins are modifed in stages as they move through the “Golgi stacks.” • Each area of stacks has its own specific enzymes that act on a glycoprotein • These enzymes are all “membrane-bound.”

  15. The process of sugar modification or “glycosylation” is so extensive and cell specific that it has its own field called GLYCOBIOLOGY.

  16. What is the Purpose of Glycosylation? • The making of short, yet sometimes complex, repeating units of sugars that get attached to proteins/lipids is different from the synthesis of DNA, RNA, proteins. • DNA, RNA and proteins are copied from templates, made in a repeated series of steps. • To make the oligosaccharides that will be attached to proteins and lipids, each molecule in the oligosaccharide is seen as a separate substrate for the next enzyme.

  17. What is the Purpose of Glycosylation? • Promotes Protein Folding • Adding sugars makes the proteins more soluble thus they don’t aggregate. • The sequence of adding sugars serves as a guide for ER-to-Golgi transport. • Protection Against Pathogens • The sugars on the outside of lung and intestinal cells form a mucus that help prevent against infection. • Cell-to-Cell Recognition • Cells will adhere to each other in the process of communicating with each other in order to direct cell movement such as in the movement of white blood cells

  18. Transport Through the Golgi Apparatus: Two Models

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