Vesicles Flashcards
Transport vesicles
Transport vesicles carry cargo form lumen and membrane of donor compartment to lumen and membrane of target compartment
Transport vesicles are coated in
Protein
Protein coated functions
1- curve the membrane to form vesicle
2- select the components to be carried
Vesicle coat is —— protein layers
Two
Outer later
Inner layer
Outer layer protein coat
Cage around vesicle
Inner layer protein coat
Adapter between outer and lipid bilayer
**select cargo proteins through affinity interactions
Classes of coated vesicles
1- CopII coated vesicles
——move materials forward from ER to ERGIC/anterograde
2- CopI coated vesicles
——move materials backward from ERGIC to ER/retrograde
3- Clathrin coated vesicles
——move materials from plasma membrane backward to endosome OR trans golgi to endosome
Budding is initiated by
Small GTP protein (GTPase)
SAR1-GDP
SAR1-GDP
GEF (guanine exchange factor) replace GDP with GTP causing conformational shift which sticks it into membrane
Sar1-gtp recruits
Sec23 and Sec24
Sec 23-24 dimer ———
Have a curved conformation, start bending the membrane
Sec 24 act as
Adaptor protein
Recruit protein to forming vesicle
Sec 24 act as
Adaptor protein
Recruit protein to forming vesicle
—— and —— binds to form cage like outer layer
Sec13 and sec31
COPII outer layer
Simple lattice
Convergence of four sec13-sec31 dimers
V-SNARE
Crucial for fusion of the vesicles to correct target membrane
Once COPII is assembled
Budding vesicle will separate from ER membrane
After separation
Protein coat must disassemble
Release component to cytosol
This allow v-SNARE to target the vesicle to proper membrane
Protein coat disassembly is mediated by
Hydrolysis of GTP, producing sar1-gdp
Vesicle travel can be mediated by
Microtubules
Locomotive (motor protein) pulling cargo(vesicles) on railroad(microtubule)
Initial contact between vesicle and target membrane involves
Tethering proteins
Two group of tethers
1- Rod-shaped fibrous proteins that form long bridges
2- Multi-protein complexes that hold membranes together
Much of membrane viscle/target is conferred by
Rab GTPases
Rab-GTP
Recruit cytosolic tether protein to membrane surface
Recruits motor protein to vesicle to facilitate transport
SNARE proteins mediate
Fusion between vesicles and target membranes
—sorting and targeting uses two families of SNAp REceptors:
1-v-SNARE
2-t-SNARE
v-SNARE found on
Vesicles
t-SNARE FOUND ON
Target membrane
v- and t- SNARE are
Complementary molecules
Their alpha helices tightly intertwine and pull membranes together
After fusion v- and t- SNARE are still
Tightly associates and in same membrane
Need NSF and SNAPS to pry apart the SNAREs using energy
COPI-coated vesicle forming is
Similar to COPII-coated
Use different coat
Endocytic pathway
Exocytosis and Endocytosis
In steady state with each other
Exocytosis
1- approach secretory vesicle to plasma membrane
2- fusion of membrane
3- rupture plasma membrane
4- discharge vesicle contents
5- vesicle membrane integrated into plasma membrane
Endocytosis
1- membrane form a pocket contain materials from exterior
2- membrane closes, forming a vesicle
3- vesicle separate from plasma membrane
Some Vesicles after budding out from TGN
Move directions to cell surface and exocytosis
consecutive secretion
Consecutive secretion may requires
Tags
Regulated secretion pathway
1- immature bud out from TGN
2- maturation = condensation
3- mature secretary vesicle move close to site of secretion
4- membrane fusion is triggered by hormonal or chemical signal
Polarized secretion
Specific proteins needs to be secreted from a limited region of plasma membrane
Polarized secretion is common in
Nerve cells
Intestinal cells
Proteins and lipids destined for polarized secretion are
Sorted into vesicles with receptors to bind the localized region
temporary regulated
Exocytosis
Proteins are released to exterior of the cell
proteins and lipid for membrane use exocytosis
Bulk-phase Endocytosis
Primates ways that cell maintain membrane and fluid balance
Clarithin-independent Endocytosis
Doesn’t ingest particular molecules—non-specific
Endocytosis (Receptor-Mediated Endocytosis)
Cell can selectively and efficiently acquire macromolecules by receptor-mediated Endocytosis
Use receptor on outer cell to internalize hormones
Receptor-Mediated Endocytosis
1-Ligands bind to their receptors on outer cell surface
2-receptor-ligand diffuse latterly
3-they encounter specialized region called coated pits
Triskelion
Clathrin molecule consist of 3 heavy chains and 3 light chains
Clathrin-coated vesicles
Clathrin molecules extensively overlap, while COPII do not
Assembly clathrin cage is promoted
Adapter protein 2
Dynamin
Cytosolic GTPases
Required for constricting the clathrin vesicle
Ingestion of large (>500nm) macromolecules or whole organisms is called
Phagocytosis
Phagocytosis in human
Mostly restricted to WBC
Endocytic vesicles then fuse with——— to degrade the target
endosome/lysosome
Lysosomes
Destroys endosomes(materials after endocytosis)
Acid hydrolase
Hydrolytic enzyme with ph=5
—capable of degrading all major classes of macromolecules
Lysosomes have highly acidic lumen
-maintain an acidic environment
-lower PH is caused by v-type ATPase that pump proton inside
Endocytic vesicle
Vesicle budding from plasma membrane as result of bulk-phase or receptor-mediated endocytosis
Early endosome
Primary sorting station in endocytic pathway
Material either recycled back or targeted for degradation
Late endosome
Organelle contain full compliment of acid hydrolase but kymen has not reached ph4-5
Lysosome
An organelle that is digestively active
Routes from late endosome to lysosome
1-ATPase pump cam lower the ph, which active the enzyme and generate lysosome
2-Late endosome fuse with existing lysosome
Endocytosis of two type of receptors
1- housekeeping receptors
2- signaling receptors
Housekeeping receptors mediate
the uptake of material that will used by cell
receptor will deliver the bound material in early endosome, releasing it because of the lower affinity at lower ph, then return to the cell membrane
Signaling receptor bind
Extracellular messengers that change activity of cell
Receptors will degraded, reducing the sensitivity of the cell
Phagocytic vacuoles material degradation
Phagocytic vacuoles become lysosoms by fusion with endosome
Vesicles formed by receptor-mediated endocytosis ———
Fuse with vesicles of TGN contain acid hydrolase
Indigestible materials
Will leave the cell
Lysosome become residual body
Nutrients of digestion
Can leave the cell(exocytosis)
Or
Release nutrient as digestion happens to the cell
Autophagy
Digestion of old organelles and cell structures
Autophagy types
Macrophagy
Microphagy
Macrophagy
Formation autophagic vacoule (autophagosome) when an organelle become wrapped in double membrane from ER
Microphagy
Smaller vacuole is formed surrounded by single membrane
