L3. Cellular Transport+Lysosomes Flashcards
What are coat proteins
- recruit cargo
- drive vesicle formation
- energy dependent process
What are the 3 different coat proteins?
- COPII: ER
- COPI: Golgi and ERGIC
- clathrin: TGN, PM and endosomes
State the process of vesicle targeting
- initiation and cargo selection:GTPase recruits coat proteins and cargo to budding site
- budding: coat assembles into spherical cage that drives vesicle formation
- scission: vesicle is released
- tethering: tethering proteins (Rab GTPases) and other tethering factors target the vesicles to the target membrane
- docking: SNARES on both vesicles and target membranes engage in fusion
- fusion: fusing of lipid bilayers between vesicles and targets
What are SNARE proteins
alpha helical membrane proteins that drive vesicle fusion
How do SNARE proteins assist in vesicle fusion
there is 1 v-sare and 3 t-snares which form coiled coils as they bind together
What is membrane traffic
coupled process between exocytosis and endocytosis
-exocytosis adds to the membrane and endocytosis balances it
What are the types of endocytosis
- phagocytosis: engulfing of large matter
- pinocyotsis: fluid, small vesicles fuses with PM
- receptor-mediated endocyotsis. ligands bind to receptor on PM and get transported into membrane
How are enzymes transported to the lysozyme?
- proteins are made in the ER and are processed in the golgi - the enzyme is phosphorylated on mannose in cis-golgi face
2, M6P receptor binds to the phosphorylated enzyme - clatharin coat assembles and the vesicle forms and leaves the ER
- the clatharin coat disocciates and the tethering proteins followed by SNARES binds the vesicle to a late endosome.
- the lower pH causes the dissociated of the enzymes and receptors, the receptors are returned to the trans golgi
- the late endosome fuses with the lysosome
Describe receptor mediated endocytosis
- receptors are present on the PM and have ligands bind to it, the clatharin coat forms and buds into cell
- clatharin uncoats and fuses with early endosomes
- early endosome fuses with late endosome of lower pH causes the receptor to release the ligand
- receptors are recycled back to the trans golgi network
- enzymes are dephosphorylated and transported to the lysosome
What are the functions of the lysosome
degrade and recycle cellular components
receive hydrolytic enzymes from the golgu
acidity maintained by proton pumps
degrade material from endocytic pathways
What are residual bodies?
material that cannot be degraded by lysosome remain in the lysosome– either get excytose from the cell
Tay Sachs
Hex-A deficiency
cannot break down lipid GM2
Xanthomas
LDL receptor deficiency on PM- means LDL cannot enter cell and be degraded by lysosomes
-cells cannot uptake LDL to make cholesterol
What are the problems posed with lipid trafficking
- hyrdophobic
- may disrupt membrane properties
What are the solutions to lipid trafficking?
- vesicles
- LTP :protein carriers for lipids
- membrane contact sites between ER junctions and other organelles
What are the 3 different classes of lipids?
- glycolipids
- splingolipids
- sterols
Lipid synthesis
- compartmentalized into different organelles
- occurs in the absence of vesicular transport
What lipid is synthesized by the mitochondria?
PC: phospatidylcholine
PS->PE->PC: after playing play station, do PE,then started eating fats while playing PC games
What lipid is synthesized by the golgi?
sphingolipid (ceramide->splingolipid)
What lipid is synthesized in lipid droplets?
cholesterol
oxidbsqualene->lanosterol->cholesterol
Lipid Transfer Proteins
(LTPs)
- highly conserved in eukaryotes
- does not have transcellular membranes
- associates with intracellular membranes
- binds lipids and membranes in traget membrane
- has a hydrophobic core to allow lipid to be buried within it.
Describe lipid transport by LTPs
free energetic process ( by diffusion)
LTP binds to donor membrane
lipid binds to hydrophobic core with lid that covers it
LTP dissociates from membrane and diffuses to the acceptor membrane
LTP unloads to lipid
LTP returns to donor membrane
How is the specificity of the transported lipids determined for LTPs?
class of LTPs and the other proteins and lipids it associates with
What are ER junctions
regions where ER comes close with other organelles
10-50nm apart
membranes do not fuse
stable structures
What are the functions of the ERJ
-excitation contraction coupling of muscles (allow Ca2+ release from SR )
mitochondria ERJ functions
apoptosis
Ca2+ trafficking
PC synthesis
What is a tethering protein?
Rab GTPase
