Flashcards in Week 2 Vesicular Transport Module Deck (48)
what are three functions of vesicular transport?
deliver newly made molecules to their final destinations, communicate with the extracellular environment, ingest extracellular particles and solutes.
What are the two major pathways of vesicular transport
secretory pathway and the endocytic pathway
what is the function of the secretory pathway
delivers newly made molecules to their proper position outside the cell
what is the function of the endocytic pathway
delivers extracellular components to the inside of the cell
where does secretory vesicular transport begin?
In general vesicles ____ off the _______ and fuse to the _______ while carrying _____
bud, donor compartment, target compartment, cargo
describe the role of protein coating in vesicle budding. what two functions does the coat play?
vesicles require a protein coat for budding. the protein coat helps pinch vesicle off donor membrane and helps sort sort the cargo
what are the three major protein coating proteins?
clathrin, COPI and COPII
Describe the structure of clathrin. how does this relate to function?
3 heavy chains and 3 light chains form a triskelion which forces vesicle into rounded shape.
How does clathrin bind the membrane of budding vesicles? (what is the binding cascade?)
Clathrin binds adaptin, adaptin binds cargo receptor, cargo receptor binds cargo
What is the role of dynamin in vesicle formation?
pinches off vesicle
what accounts for the variation in cargo carried by vesicles?
different adaptin molecules bind different cargo receptors in different regions of the cell.
What happens to the clathrin coat prior to the vesicle reaching the target compartment?
clathrin and adaptin are released from the vesicle and recycled
how does the vesicle find its way to the target compartment?
it moves along cytoskeletal elements within the cytoplasm
which proteins are responsible for docking and recognition of vesicles to target compartments?
Rab located on the vesicle binds the tethering protein located on the target membrane
which proteins are largely responsible for the fusion of the vesicle with the target membrane?
v-snare on the vesicle and t-snare on the target compartment
What types (3) of modifications or proteins occur in the ER?
Cys-Cys Disulfide bonds (interchain and intrachain)
lipid membrane anchors (addition of lipids that covalently anchor protein to the membrane
The initial glycosylation of proteins occurs in the ER
Oligosaccharides are generally added to which residues on a polypeptide chain?
what is the difference between N-lonked and O-linked glycoproteins?
N-linked: oligasaccharide added to Asn residue
O-linked: added to Ser or Threonine
what is the role of dolichol?
dolichol is a special membrane lipid in the ER that transfers its oligasaccharide group to the newly translated polypeptide
Describe the selectivity of exit from the ER
protein exit from the ER is highly selective. The ER uses chaperone proteins to ensure proteins fold correctly. If a protein cant be made to fold correctly it is degrade in cytosol
what is the difference between cis-golgi network and trans-golgi network?
Cis: where vesicles enter the golgi
Trans: where vesicles exit the golgi
Vesicles that exit the golgi are destined to go where?
endosome or plasma membrane
as a vesicle moves through the golgi what happens to its contents?
further sorting and modification of sugars and proteins
What are the two pathways of exocytosis
constitutive secretion, regulated secretion
describe constitutive secretion. what cells do this? role?
constantly occuring and seen in all cells. supplies PM with new proteins and lipids and releases things to extracellular space
describe regulated secretion. what cells do this? role?
release of vesicle contents to extracellular space in response to specific stimulus (receptor activation). only seen ins specialized secretory cells such as endocrine cells
what is the pathway of an ER protein from the ER to lysosome?
ER-->cis golgi-->trans golgi-->endosome-->lysosome
what is the role of lysosome? what type of enzymes to they house?
sites of molecular degradation. House acid hydrolases (nucleases, proteases, lipases)
describe the pH of a lysosome. how is it maintained?
acidic (pH about 5. compare to pH 7.2 see in cytosol). maintained through hydrogen pumps
where are all lysosomal proteins translated?
by ER bound ribosomes
what protects acid hydrolases from the acidic environment of the lysosome?
acid hydrolases are heavily glycosylated in the ER to protect them from the low pH
what is the role of Mannose-6-phosphate? where is it added?
Mannose-6-phosphate is added to lysosomal acid hydrolases within the GOLGI. M6P binds M6P receptors of clathrin coated vesicles. These vesicles are targeted to endosomes.
compare early and late endosomes. Location? Acidity?
early: located near PM, slightly acidic (pH of 6.2)
late: located in interior of cell, more acidic (pH of 5.5). will mature into lysosome
what is I-cell disease? cause? results?
enzyme that adds M6P (within golgi) is defective. therefore acid hydrolases are not targeted to endosomes and end up in blood.
What are the three types of endocytosis?
phagocytosis, pinocytosis, receptor-mediated endocytosis
What is phagocytosis? where is it seen?
ingestion of large particles (bacteria and cell debris). immune cells
what is pinocytosis? where is it seen?
ingestion of fluid and small molecules. seen in all cells
What is receptor-mediated endocytosis? what does it accomplish?
a mechanism that allows concentrated uptake of specific molecules
what offsets the loss of membrane through pinocytosis?
is pinocytosis clatherin dependent?
it can be, but not always
describe the process of receptor-mediated endocytosis
specific cargo bind cargo receptors on (facing extracellular space)-->clathrin coated pits are formed (adaptin binds cargo receptor, clathrin binds adaptin)--> the vesicle buds INTO the cell and is ready to fuse
What is the role of early endosomes?
sort endocytosed material
what are the fates of receptors used in receptor mediated endocytosis?
1. recycled to PM
2. degraded by lysosome
3. transocytosis: travel across a cell
how does the cargo know to release when it contacts an early endosome? what if it doesnt release?
the light acidic pH of the early endosome triggers cargo release. If the cargo is not released it will have the same fate as the receptor.
how is cholesterol transported in blood?
transported as LDL: a core of cholesterol with a lipid monolayer that is organized by a protein.
How do cells take in cholesterol from blood?
LDL receptors locate LDL and entire LDL molecule is taken up (receptor mediated endocytosis)