1. Intracellular Vesicular Traffic
ER to Golgi
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2. Golgi Apparatus Functions include: Carbohydrate synthesis
-pectin and hemicellulose in plants
-extracellular matrix in animals
Carbohydrate synthesis onto proteins
Sorting of products from the ER

3. Types of Coated Vesicles
ER exit sites

4. Formation of ER Transport Vesicles
Proteins that need to return to the ER:
Cargo receptors
-Contain exit signals
-Some are lectins
(ERGIC53 – clotting)
2. Resident ER proteins

5. Antibody Retention/Secretion
-Chaperone proteins (calnexin, BiP) retain misfolded or incomplete proteins in the ER
-They cover up exit signals
-ER imports peptide fragments
-Cystic Fibrosis, misfolded protein is retained in ER

6. Homotypic Membrane -Fusion of membranes from the same compartment
Vesicular
tubular
cluster
-Heterotypic fusion – a membrane from one compartment fuses with the membrane of a different compartment

7. Vesicular Tubular Clusters
-The clusters are short lived
-They move along microtubules to the Golgi while some are involved with transport back to the ER

8. Retrieval of ER Resident Proteins
-ER Retrieval signal
-KKXX or KDEL
-Lys-Asp-Glu-Leu
-KDEL receptors can bind directly to COP I coat proteins

9. Retrieval of ER Resident Proteins
-The affinity of the KDEL receptor changes depending on the compartment it is in
-Some proteins do not have return signals and are returned to the ER at a slower rate

10. Kin Recognition
-Retention of proteins within a compartment through their aggregation
-ER resident proteins may aggregate forming complexes
-Large number of proteins interacting with lower affinity

11. Golgi Apparatus
Animal Cells

12. Golgi Apparatus
Plant Cells

13. Golgi Apparatus ER side
During passage through the Golgi, molecules are covalently modified

14. Golgi Compartmentalization
Unstained
Stained
Acid
Phosphatase
trans Golgi
network
Nucleoside
Diphosphatase
trans

15. Golgi Compartmentalization
-Oligosaccharide
processing
-Resident proteins of the Golgi are all membrane bound
-Glycosidases and glycosyl transferases

16. Goblet Cell of Small Intestine
-There are more Golgi in cells specializing in secretion

17. N-Linked Glycosylation
-Glycoproteins – proteins containing sugar residues
-Linked to Asparagines in the sequences
Asn-X-Ser and Asn-X-Thr, where X cannot be Pro
-Transfer is catalyzed by oligosaccharide transferase which has its active site on the lumenal side of the ER

18. Precursor Oligosaccharide Synthesis
-The sugars are first activated in the cytosol by forming nucleotide-sugar intermediates
-O-linked oligosaccharides
are linked to hydroxyl
groups of Ser and Thr
residues and this
occurs in the Golgi

19. Protein Glycosylation
The precursor oligosaccharide is held in the ER membrane by a long and very hydrophobic lipid molecule, dolichol

20. Two Classes of Oligosaccharides

21. Two Classes of Oligosaccharides
Most are
complex
-Trisaccharide unit – GlcNAc-Gal-Sialic acid

22. Oligosaccharide Processing

23. Models of Golgi Organization
Static model
Dynamic Model