Cellular Logistics: Vesicular Traffic - Secretion & Endocytosis Flashcards
Where is cargo transported from and to in Foward Transport in the secretory pathway?
ER to cis-Golgi
Where is cargo transported from and to in Reverse Transport in the secretory pathway?
cis-Golgi to ER
Is Forward Transport Anterograde or Retrograde transport?
Anterograde
Is Reverse Transport Anterograde or Retrograde transport?
Retrograde
Which type of coated vesicles is involved in Forward Transport?
COPII coated vesicles
Which type of coated vesicles is involved in Reverse Transport?
COPI coated vesicles
In Reverse Transport, what sequence mediates the retrieval of most missorted soluble ER resident proteins to the ER?
C-terminal KDEL sequences
(Lys-Asp-Glu-Leu)
In Reverse Transport, what sequence mediates the retrieval of transmembrane ER resident proteins?
C-terminal KKXX sorting signal
(Lys-Lys-X-X)
Which model is widely favoured for transport through the Golgi?
Cisternal Progression Model
What type of vesicles mediate forward transport through the Golgi?
Retrograde vesicles
Which coated vesicles mediate retrograde vesicular transport in the cisternal progression model of transport through the Golgi?
COPI
What method can be used to study the secretory pathway?
Pulse-Chase Method
What is involved in the Pulse part of the Pulse-Chase Method?
- Tissue is exposed briefly to radioactive H3 Leucine
- H3 Leucine incorporated into newly synthesised protein
What is involved in the Chase part of the Pulse-Chase Method?
Subcellular localisation of labelled proteins examined at various timepoints
How many classes of secretion (sec) mutants have been identified in the study of secretion pathways in yeast?
5 classes
What type of coated vesicles mediate transport from Trans-Golgi to Endosomes?
Clatharin Coated Vesicles with associated Adapter Proteins (AP
What is the structure of Clatharin?
Three limbed structure called a Triskelion
How does Clatharin achieve a curved structure?
Triskelions polymerise to form a curved polygonal lattice
What is the inner layer of the Clatharin coated vesicles composed of?
Adapter protein complexes
What is the final step of vesicle budding for Clatharin coated vesicles?
Budding Off
What does Budding Off require for Clatharin coated vesicles?
GTP hydrolysis
Which GTPase forms a ring around the “neck” of a Clatharin coated vesicle in order for it to bud off?
Dynamin
TRUE OR FALSE:
GTPases are required for pinching off of COPI and COPII vesicles
False.
They are NOT required
TRUE OR FALSE:
In the the secretory and endocytic pathways, the outer Clatharin coat remains the same but the adapter proteins and sorting signals on the cargo proteins are different?
True.
What Adapter Proteins are involved in trafficking vesicles from Golgi to Endosomes?
AP1 or GGA
What Adapter Proteins are involved in trafficking vesicles from Plasma Membrane to Endosomes?
AP2
What Adapter Proteins are involved in trafficking vesicles from Golgi to Lysosomes?
AP3
TRUE OR FALSE:
Sorting signals on cargo proteins or cargo receptors interact with Clathrin?
False.
Sorting signals interact with the adapter proteins
What type of modification happens on Sorting Signals on proteins heading to the lysosomes?
Carbohydrate modifications
* Mannose-6-phosphate
Where does sorting signal modification occur?
cis-Golgi
What are the steps involved in Sorting Signal modification?
- Attachment of phosphorylated N-acetylglucosamine (GlcNAc) to Mannose
- Removal of N-acetylglucosamine to leave Mannose-6-phosphate (M6P)
What are the TWO enzymes involved in the carbohydrate modification of Sorting Signals?
- GlcNAc phosphotransferase
- Phosphodiesterase
What type of proteins do Mannose-6-phosphate (M6P) receptors bind to?
Proteins with M6P modified oligosaccharides
What pH causes release to M6P tagged cargo proteins in endosomes?
Low pH (5 - 5.5)
How are lysosomal storage diseases characterised?
Absence of one or more lysosomal enzymes
Which enzyme do cells lack in I-cell disease (lysosomal storage disease)
N-acetylglucosamine phosphotransferase
TRUE OR FALSE:
Lysosomal enzymes are NOT tagged with Mannose-6-phosphate in I-cell disease
True
What happens to enzymes in I-cell disease?
Enzymes are secreted instead of being sorted
What are the TWO types of secretory vesicles of the secretory pathway?
- Constitutive
- Regulated
What is an example of a Constitutive secretory vesicle?
Serum albumin release from hepatocytes
What is an example of a Regulated secretory vesicle?
Neurotransmitter release from synapses
What serves as a sorting signal for Regulated secretion?
Selective aggregation of proteins
Where does proteolytic cleavage occur on secreted proteins in secretory vesicles?
C-terminal to dibasic motifs
(Lys and Arg)
What are TWO types of Endocytosis?
- Pinocytosis
- Receptor mediated endocytosis
What does Receptor Mediated Endocytosis involve?
Binding of an extracellular ligand to a receptor
What are THREE examples of ligands that are endocytosed?
- Transferrin (iron binding protein)
- Low-density lipoprotein
- Growth factors and hormones
What is a Low-Density Lipoprotein (LDL) comprised of?
- ApoB protein
- Phospholipid shell
- Cholesterol in core
What is Familial Hypercholesteromia (High Cholesterol) caused by?
Mutations in the LDL receptor
What did the study of disease causing mutations in the LDL receptors lead to?
Identification of the NPXY sorting signal for endocytosis
Where does NPXY sorting signal bind to?
AP2
What is the function of Transferrin?
Transports iron in the bloodstream
* from the intestine and liver
* to cells in all tissues of the body
What binds to the Transferrin Receptors on the plasma membrane and is endocytosed?
Ferrotransferin
