Vesicle trafficking Flashcards
Vesicular trafficking def
the process by which vesicles transport mateirlas between diff, cellular compartments/ between cell and environment
compare and contrast endo and exocytosis
ENDO: nutrient uptake/cell signaling/change in cell shape/ controls cell response to external environment
EXO: release of cargo molecules
!! BOTH: control the composition of the plasma membrane
2 types of exocytosis and mechanisms
- CONSTITUITIVE:
-COP coated vesicles
-not dependent on specific stimulation
-continuous process (products are immediately secreted so there is no accummulation of vesicles)
-USED BY: plasma cells for immunoglobulins and fibroblasts for procollagen - REGULATED:
-cathrin coated vesicles
-control of specific stimulation (Ca2+ transient flux)
-stimulates the fusion of vesicles with plasma membrane
embedding def
vesicle originates from a cell compartment and it travels to a diff cell compartment (eg. vesicles from ER go to Golgi)
3 types of endocytosis
- receptor mediated
- phagocytosis
- pinocytosis
components needed for endocytosis
- ATP
- Ca2+
- cytoskeletal elements for motility (microfilaments)
2 types of phagocytosis
DIRECT: recognition of oligossacharides on pathogen surface
INDIRECT: recognition of antibodies on pathogen surface
!! both are receptor mediated
process of phagocytosis (3 steps)
- recognition of particle to be ingested
- formation of pseudopods (polymerisation of actin)
- internailsation of the particle forming a phagosome
!! then combines with lysosomes to hydrolyse
disorders stemming from phagocytosis malfunction
GENETIC DISORDERS:
1. neutrophill differentiation malfunctions
- motility malfunctions
- specific enzyme malfunctions which alters the ability to digest the particle
pinocytosis definition and 2 types
DEF: non specific introduction of small liquid droplets from environment into cell
- MACRO:
-clathrin independent, actin dependent
-for nutrients and antigens
-regulated by GFs - MICRO:
-clathrin AND actin independent
-for fluids and small moclecules
-involves calveolin and flotilin proteins
receptor mediated endocytosis (6 steps)
- cargo binds to receptor and is coated with clathrin
- binding changes conformation of receptor - causes interaction with adaptin protein
- adaptin favors connection between cargo/clathrin
- invagiation of membrane forming the coated pit and then vesicle
- dynamin protein forms spiral on the base of vesicle and closes the vesicle up –> dettachment into cytoplasm
- dettachment of clathrin and recycling back into membrane to be reused
endosomes def
membrane bound vesicles associated with the endocytic pathway
2 hypothesis for biogenesis of endosomes
- STABLE COMPARTMENT MODEL: stable compartment connected through vesicle with extracellular environment and golgi fusion due to specific receptors
- MATURATION MODEL: formed denovo by endocytic vesicle origniating from plasma membrane (removal of specific receptors)
types of endosomes
- early: ph 6.5, located near plasma membrane, lumen is divided into cisternae
- late: ph 5.5, located deeper in cytoplasm (near golgi/nuc), ph drop is due to membrane pumps for H+ intake
- lysosome: most mature, ph 5, contains lytic enzymes
what is necessary for the maturation from the late stage endosome to lysosome
-newly synthesised lysosomal enzymes
-synthesis of proteins needed:
SOLUBLE PROTEINS: addition of mannose 6 phosphate residues
MEMBRANE PROTEINS: short cytoplasmic C terminus domain recognised by adaptin and secrete clathrin coated veicles
function of lysosomes
main site of cellular digestion, destroy microorganisms or damaged cells
structure of lysosomes
-heterogenous/variable morphology and shape
-contain acid hydrolases
-ph5
-H+ membrane pumps
-membrane glycoproteins that protect inner surface from the internal lytic enzymes
4 models of lysosome biogenesis
- maturation (from early and late endosomes)
- vesicular transport
- kiss and run: late endosome contact site with lysosome and transfer of cargo
- fusion/fission: forms hybrid organelle followed by lysosome reformation
visualisation of lysosomes
-use of tracker to mark one of its components
-staining cells embedded in paraffin with histological dyes (toludeine blue)
-fluorescent microscopy
exceptions to normal behaviour of lysosome secretion
NORMAL: they would only release enzymes within the space of the organelle itself
EXCEPTIONS: contents are released out of the cell
1. SPERM: acrosome released for destruction of zona pellucida
2. OSTEOCLASTS: bone resorption
3. PHAGOCYTOSIS: release within phagolysosome
primary secondary and tertiary lysosome
PRIMARY: sacs with enzymes, without substrate
SECONDARY: larger, formed by fusion of the primary lysosome with the phagosome
TERTIARY: contain residues of material that can no longer be broken down, such as lipofuscin.
example of n undigested body
LIPOFUSCIN: remains inside cell (especially neurons)
lysosomal storage sisorders
-usually genetic
-there is absence of one or more proteins and enzymes
-undigested material/residual bodies accummuate in cells
process of autophagy and 3 types
DEF: self destruction of cells by internalising ‘damaging’ cytoplasmic components into the lysosomes
- MACRO: cytoplasmic portion is surrounded by double membrane to form autophagosome. This then fuses with lysosome for digestion
- MICRO: cytoplasmic proteins internalised into lysosomes by invagination of lysosomal membrane
- CHAPERONE MEDIATED: chaperone mediates transport into lysosome lumen (MOST SELECTIVE PROCESS)
transcytosis def
used for transport of substances from one end of the cell to the other –> receptor mediated
Types of protein coats a vesicle can have (3)
- clathrin –> vesicles undergoing endocytosis
- COP1 –> movement from Golgi to RER (retrograde)
- COP2 –> movement from RER to Golgi (anterograde)
purpose of vesicle coating (2)
- favours bending of the membrane to form vesicles
- influences selection of cargo components to be inserted and transported into vesicle
Structure of the clathrin
-hexameric protein (3 light and 3 heavy chains)
-arranged in 3 arm TRISKELION
-surrounds vesicles
how are transport vesicles directed to SPECIFIC target organs?
v-SNARE on vesicles bind to t-SNARE transmembrane proteins on target organelle.
!! link and interaction between the two forms the fusion complex
