INTRACELLULAR TRAFICKING Flashcards
ENDOCYTOSIS
– Clathrin-mediated endocytosis (receptor-dependent)adaptin
– Potocytosis (receptor-dependent in caveolae)
– Macropinocytosis
– Phagocytosis
• exocytosis
– constitutive
– regulated (Ca2+ triggered)
Formation of vesicle
Initiation, invagination, constriction, fission, uncoating
From ER–> golgi
COP II by help of Sar1 (GTP binding protein)
From golgi–>er/ PM
COP I by help of ARF (GTP binding protein)
Rab
control most steps of vesicle transport
Recognition of the target membrane through
SNARE
v-snare and t-snare
v=vesicle t=target membrane
Actin
• Globular proteins (α,β,γ types)
• polarized polymerization (pointed and barbed ends)
• function: (moving organelles, cellular motion
cell adhesion structures, maintenance of cell volume
Intermediate filaments
No polarity No motor proteins associated High tensile strength Resistant to compression, twisting and bending forces Heterogeneous
Microtubules
• polymers of tubulin subunits
• alpha and beta-tubulins
• polarized polymerization (- and + ends)
• tube formed by 13 polymers (23 nm diameter)
• negative end at the microtubule organizing center
(MTOC): centriole or basal body
• function: organelle movements, mitotic spindle,
cilia and flagella
Colchicine
“mitotic poison” or spindle poison
binds to tubulin and inhibits
microtubule polymerization
Motor proteins associated to microtubules:
dyneins and kinesins
Translocation complex in mitochondria
TOM and TIM
NLS
Nucleas localization signal that interact with importins and ran
Ran GAP
RAN + GTP–>RAN GDP with help of Ran GAP
RAN GEP
Ran GDP–> ran takes away Gdp from RAN in nucleus
SRP
signal recognition particle at N-terminus of poly Pwhich interact with SRP-receptor and GTP gets hydrolyzed
translocon
3 membrane protein, forming a protein conducting channel in ER
signal peptidase
cleavage of SNP of protein
how does protein bind to translocon
by hydrophobic interactions
PTS
PTS 1 on carboxyl termianal
PTS2 on amino terminal
PEX 5
PTS 1 forms complex with pex 5
PEX 7
PTS 2 forms complex with pex 7
ATP in peroxisom
Matrix proteins need ATP and membrane proteins doesnt
Chaperone
assist in covalent folding or unfolding of proteins
Hsp 70
Acts as chaperone in mitochondria preventing folding of protein
BIP
Binding immunoglobin protein
prevents aggregation and prompts proper folding
Example of post translational translocation
Cytochrome B5
KDEL
ER retention signal
golgi–> er cop I
ERAD
ER associated degradation
takes care of proteins that have been missfolded to enter proteasomes
P97
ATP source for ERAD
Two pathways for degradation
Lysosomal proteases, NO ATP
Ubiquitin, ATP
Enzymes of protein degradation
E1-activation enzyme
E2- conjugation enzyme
E3- ligase enzym
Minimuma amount of ubiquitin molecules to be present to degrade protein
4
The endomembrane system
- nuclear envelope
- endoplasmic reticulum (ER)
- Golgi apparatus
- lysosome (phagosome, autophagosome)
- endosome
- transport vesicles
- cell membrane
- peroxisome (?)
Mitochondria
• inner and outer mitochondrial membranes
N-linked glycosylation
The attachment of oligosaccharide, glycan to a nitrogen atom (amide nitrogen of asparagine (Asn) residue of a protein in ER
Function of golgi
glycoprotein maturation O-glycosylation limited proteolysis protein sorting synthesis of sphingomyelin, glycolipids, proteoglycans, polysaccharides, glucosaminoglycans
Lysosome
Its enzymes can break up almost anything.
Enzymes in lysosome
– DNAse, RNAse – proteases (e.g. cathepsins) – glycosidases – lipases – phosphatases – sulfatases
Mitochondria matrix
Matrix nucleoid, ribosomes, large enzyme complexes
Mitochondria Inner membrane
impermeable
protein: lipid ratio > 3:1
- transporters for metabolites and proteins
- enzymes of oxidative phosphorylation
- proteins of fusion and fission
Mitochondria outer membrane
pores (porin)
permeable for up to 5 KDa
N-glycosylation
dolichol
arginine, glucose, mannose, N-acetylglucose-amine
