Secretory Pathway Flashcards
Describe the oath of the secretory pathway
ER to golgi to plasma membrane
Describe the path of the endocytic pathway
Cell surface to endosome to golgi/ER/endosome
How does material move from the rough ER to golgi?
Vesicle fusion
What does the trans golgi do?
Sorts out constitutively secreted proteins without the ned for signals
Where does glycoslation take place?
ER
What sorts of glycosylation can take place?
N- linked on Asp
O- linked on S/T
Describe how an Asp N-link forms
- Pre-formed oligosaccharide is added to an Asp in the ER
- Oligosaccharides are added and processed throughout the secretory pathway
- Oligosaccharides are trimmed and more sugars are added in the golgi
Why are proteins glycosylated?
Assist in folding
Can act as a ligand for intracellular trafficking/sorting and interactions with the extracellular matrix + proteins/sugars on other cells
What makes a suitable model organism to study cellular processes?
Simplicity- so single celled organisms
Allows analysis of specific types of secretion
What are some advantages of studying yeast for the secretory pathway?
Can do genetic studies between haploid and diploid
The entire genome sequence is known and fundamental pathways have been conserved
Cheap and easy to grow in large quantities
Limited gene diversity
What are some disadvantages of studying yeast for the secretory pathway?
Limited cell-cell contact, so not informative for multicellular organisms
Small (5μm) so high resolution imaging is difficult
Cell wall can prevent some studies such as microinjections
What hypothesis did Novick and Schekman have in 1980?
If proteins couldn’t be secreted (sec-), the cell density would increase as vesicles carrying the protein accumulates
What experiment did Novick and Schekman do in 1980?
Cells were analysed for their abilities to secrete invertase and acid phosphate at permissive and restictive temperatures
Secretory mutants synthesised by didn’t secrete them.
Heavier cells were analysed with electron microscopy to find alterations in ultrastructure, e.g accumulation of vesicles
How many genes were identified in Novick and Schekman’s experiments?
23
These were ordered by combining mutants from different classes
Describe the progress of α factor throughout the secretory pathway
- Modified in the ER by oligosaccharides
- Sugars are added in the golgi
- Proteolytically cleaved into 4 peptides before secretion
Why weren’t all the genes in secretory and exocytic pathway identified by Novick and Schekman?
Only temperature sensitive mutants were identified
Only secretion to the plasma membrane was identified- nothing to endosome or vacuole
Redundantly (rarely) functioning genes wouldn’t be identified
Where does the decision to traffic to the surface or lysosome take place?
Trans-golgi network
What pathways are affected by mutations between the endosome and lysosome?
Biosynthetic and degradative pathways
What is endocytosis?
Process where the plasma membrane invaginates into the cell
Produces a vesicle that can fuse with endosomes and enter the endo-lysosomal membrane system
What is the importance of endocytosis?
Retrieves molecules from the secretory vesicle for recycling
Downregulates certain signals
Remodels the cell surface
Describe the path of endocytosis
Plasma membrane
Endocytic vesicle
Early endosome
Late endosome
Golgi or vacuole
How were mutants in endosomal pathway identified?
End- screens looked at mutatants tht could not internalise lucifer yellow or an α-factor (pheromone)
What does the lysosome (vacuole) do?
Degrades extracellular material from endocytosis
Degrades intracellular components through autophagy
It’s proteolytic enzymes are kept separate from the rest of the cell
How are lysosome enzymes transported to the lysosome?
Secretory pathway and sorted at the trans-golgi network
