Endomembrane System Part 2 Flashcards
1
Q
Golgi Complex
A
- ‘complex’ or ‘stack’ of flattened, membrane-bound cisternae (sacs) with dilated edges and numerous associated tubules and vesicles
- number and distribution of them vary between different cell types (mammals contain one large one, and plants/yeast contain many small)
- possesses several subcompartments (results in complex (stack) having distinct polarity: both structurally and functionally)
-
Location of Protein modification (N-linked glycosylation continued and phosphorylation of mannose
groups (M6P) for protein targeting to lysosomes) - discovered by Camillo Golgi (1898)
2
Q
Cisternae
A
- embrane-bound sacs with dilated edges and numerous associated tubules and vesicles
- 3+ make up the Golgi Cisternae
3
Q
cis-Golgi network (CGN)
A
- consists of complex, interconnected network of tubules and vesicles adjacent to ERES
- located at cis face of Golgi complex
- initial destination of COPII transport vesicles from ERES
- serves as a ‘sorting station’…:
- destination (‘acceptor’ compartment) of COPII vesicles coming ‘forward’ (anterograde transport) from ERES to CGN
- site of COPI vesicle assembly for transport ’back’ (retrograde
transport) from CGN to ER - ‘forward’ (anterograde) transport as CGN matures into next subcompartment of Golgi complex (i.e., CGN → cis cisternae)
- destination of COPI vesicles moving ‘back’ (retrograde transport) from next subcompartment of Golgi complex (
cis cisternae) to CGN
4
Q
Golgi Cisternae (cis, medial and
trans)
A
- series of three or more large, flattened cisternae (makes up most of the golgi)
- main sections: cis, medial and trans cisternae
- sites of Golgi metabolism (synthesis of complex polysaccharides used for cell wall and modification (glycosylation) of proteins/lipids & phosphorylation of mannose units in lysosomal-destined proteins)
- Golgi cisternae act as ‘assembly line’ in N-linked glycosylation:
- core oligosaccharides on proteins moving through Golgi modified sequentially (in various ways) by different enzymes in
each subcompartment (cis, medial and trans Golgi cisternae possess unique glycosyltransferase and glycosidase enzymes)
5
Q
trans-Golgi network (TGN)
A
- interconnected network of tubules and vesicles ( » CGN)
- located on trans face of Golgi complex
- serves as ‘sorting station’ ( » CGN)…:
- ‘forward’ (anterograde) transport as previous subcompartment of Golgi complex matures into TGN (i.e.,
trans cisternae → TGN) - site of clathrin coat vesicle assembly for transport ‘forward’
(anterograde transport) from TGN to endosomes - site of secretory vesicle and secretory granule assembly
for transport ‘forward’ (anterograde) to pm (secretion into
extracellular space) - site of COPI vesicle assembly for transport ’back’ (retrograde)
to Golgi trans cisternae
6
Q
Golgi matrix
A
- consists of various Golgi peripheral and integral membrane proteins (ex. GRASPS)
- mediates organization of Golgi complex (stack)
- links Golgi complex to cytoskeleton (positioning and movement of Golgi (like all organelles/vesicles) in cell controlled by interaction with cytoskeleton)
- cytoplasmic-facing domains interact to form ‘scaffold’ – link CGN, cis/medial/trans cisternae, and TGN together
7
Q
GRASPs (Golgi reassembly and stacking proteins)
A
- serve as ‘tethering proteins’ to link different Golgi subcompartments together – RNAi of GRAPS results
Golgi complex disassembly
8
Q
N-linked glycosylation
A
- most glycoproteins (synthesized & N-linked-glycosylated in RER) moving through Golgi ( cis -> trans) subjected to additional
glycosylation reactions - core oligosaccharides on proteins moving through Golgi modified sequentially (in various ways) by different enzymes in
each subcompartment
9
Q
a-mannosidase I
A
- found within the cis cisternae, and removes 3 mannose sugars from core oligosaccharide of glycoprotein during N-linked glycosylation
10
Q
Mannose-6-phosphate (M6P)
A
- in cis cisternae, mannose units in core oligosaccharide(s) of soluble proteins destined for lysosomes are phosphorylated with these residues
- N-acetylglucosamine phosphotransferase recognizes unique sequences in lysosomal-destined proteins
- prevents lysosomal-destined proteins from being subjected to N-linked glycosylation reactions
Basically…
- proteins without this are packaged at TGN into
secretory transport vesicles/granules destined for
plasma membrane/extracellular space (via constitutive
and regulated secretion pathways) …..or reside in Golgi
- proteins with this are packaged at TGN into clathrin-
coated transport vesicle to endosomes and then
lysosomes (via the biosynthetic pathway)
11
Q
Signal patch
A
- targeting signal consisting of specific 3D arrangement of molecules (e.g., sugars) on folded protein’s surface
- Distinct from the polypeptide-based targeting signal (e.g., NLS and signal sequence involved in nuclear and ER targeting, respectively)
- M6P acts as a one of these
12
Q
N-acetylglucosamine phosphotransferase
A
- recognizes unique sequences (M6P)
in lysosomal-destined proteins
13
Q
Cisternal progression/maturation model
A
- Golgi is a dynamic structure: each subcompartment continually moves (forward) fromcis to
trans side of Golgi complex - Golgi complex persists ( structurally & functionally)
because COPI transport vesicles continually move
resident Golgi proteins ‘back’ (retrograde transport)
to proper subcompartment
It’s essentially a constant flow of forward and backwards motion that just goes on forever lolol idk how to explain this do your own research pfft
14
Q
COPI
A
- COPI-coated vesicles move backwards (retrograde transport) between Golgi subcompartments
15
Q
Lysosome
A
- digestive organelle – degrades all types of macromolecules
- plays key role in degradation of larger cellular components/organelles (autophagy)
- contains ~60 different soluble acid hydrolyase enzymes
enzymatically active only at low pH of lysosome interior (lumen) - products of degradation are transported into cytoplasm
- low pH in lysosomal lumen maintained by membrane-bound ATPase proton pumps
- highly dynamic: lysosomes possess wide variety of shapes and sizes depending on organism/tissue/cell type
16
Q
Autophagy
A
- degradation of larger cellular components/organelles
17
Q
Acid hydrolyase
A
- responsible for breakdown of materials within lysosomes (contains ~60 different ones)
- enzymatically active only at low pH of lysosome interior (lumen)
18
Q
M6P receptor
A
- integral transmembrane protein that mediates subsequent
concentration of soluble lysosomal (‘cargo’) proteins into nascent clathrin-coated transport vesicles - in the TGN, soluble M6P-bearing lysosomal
destined proteins (e.g., acid hydrolyases)
recognized by M6P receptor - lumenal-facing domain of M6P receptor binds
to M6P groups on soluble lysosomal-destined
proteins in lumen of TGN
19
Q
Clathrin-coated transport vesicle
A
- transport materials to the lysosomes (proteins with M6P: TGN → clathrin-coated vesicle → late endosome → lysosome)
20
Q
AP1 and GGA (AP complex)
A
- mediate vesicle ‘cargo’ section and serve as ‘linker’ for clathrin-coat vesicle assembly
- cytoplasmic-facing domain of M6P receptor binds to AP1 and GGA adaptor coat proteins
- recruitment of AP1/GGA adaptor proteins from cytoplasm to TGN surface mediated by GTPase Arf1
21
Q
Arf1
A
- mediates recruitment of AP1/GGA adaptor proteins from cytoplasm to TGN surface
- Arf1 binding to GTP causes conformational
change; exposed lipid anchor in Arf1-GTP directs it from
cytoplasm to outer leaflet of TGN membrane; initiates outward bending of membrane
22
Q
Clathrin: triskelion
A
- clathrin triskelions recruited from cytoplasm self-assemble to form outer ‘scaffolding’ (cage-like lattice) of ‘coat’ on growing vesicle clathrin assembly promotes curvature (outward bending) of TGN membrane
- one molecule of clathrin consists of
three ‘light’ chain polypeptides & three
‘heavy’ chain polypeptides - individual clathrin triskelions initially assemble to form hexagons that lie flat on membrane (cytoplasmic) surface
- triskelions subsequently self-assemble to form pentagons
23
Q
Dynamin
A
- mediates release (scission) of clathrin-coated vesicle from TGN membrane into cytosol; results in breakdown of clathrin-coat upon release
- dynamin recruited from cytosol to connection (‘stalk’)
between growing clathrin-coated bud and TGN membrane - dynamin proteins assemble to form dynamin ring
around stalk - GTP hydrolysis causes a conformational change in
dynamin ring resulting in twisting and ‘pinching off’
(scission) of nascent vesicle
24
Q
Scission
A
- release of a vesicle from wherever it was forming, so it can begin its epic journey
Didn’t know what to write for this one either lolol so this was what you get
25
gamma-GTP
- ***incubation of cell with gamma-GTP (non-hydrolyzable analog of GTP) causes continued dynamin ring polymerization, resulting in long, extended ‘stalk’ and no scission of vesicle bud***
26
Late endosome
- ***junction of biosynthetic and endocytic pathways***
- acidic interior (~pH 5.0-5.5 in lumen) of late endosomes causes M6P receptors to dissociate from soluble lysosomal ‘cargo’ proteins (acid hydrolases)
- eventually, late endosome fuses with lysosome (late endosome trafficking and docking/fusion with lysosome mediated by organelle-specific Rab/Rab effectors and SNARES)
27
Retromer transport vesicle
- ***‘empty’ M6P receptors ‘recycled’ back to TGN via retromer-coated vesicles (retromer complex ‘coat’ assembles on cytoplasmic surface of late endosome, and is destroyed after scission)***
- retromer vesicles (w/ various pm cargo and
‘empty’ M6P receptors) also traffic to
plasma membrane
28
Receptor-mediated endocytosis
- ***M6P receptor-cargo protein complexes
at pm retrieved by receptor-mediated
endocytosis and delivered back to
late endosome***
29
Constitutive secretion pathway (default pathway)
- ***materials continually transported
(via secretory vesicles) from TGN to pm***
- vesicles fuse (via Rabs & SNAREs) with
pm and release (exocytosis) their lumenal
soluble ‘cargo’ outside of cell
- pathway for proteins not selectively
sorted through biosynthetic pathway
(i.e., targeted to late endosomes and
lysosomes) OR by regulated secretion
30
Phagocytosis
- ***uptake of large, particulate materials from
extracellular space by specialized cells***
- ex. Recognition and removal of bacteria by leukocytes
31
Fc receptor
- ***leukocyte plasma membrane Fc receptors recognize exposed Fc domain on antibodies bound to bacterium and signal re-assembly of actin microfilament network (pseudopods)***
32
Fc domain
- ***bacteria identified by immune system as ‘foreign’ material and
generates antibodies containing Fc domains against bacterial cell-surface components***
33
Pseudopod
- ***alterations in cytoskeleton result in changes in shape ofof leukocyte; cell extensions = pseudopods, which allows engulfing of bactrium***
34
Phagosome
- ***eukocyte pm engulfs (pseudopods) bacterium and fuse to form phagosome***
35
Bulk-phase endocytosis: Pinocytosis
- ***non-specific uptake of extracellular fluids and plasma membrane proteins and lipids into small vesicles***
36
Receptor-mediated endocytosis
- ***specific cell-surface (pm) receptor binds extracellular ligand(s) and receptor-ligand complexes subsequently concentrated and internalized in clathrin-coated transport vesicles***
Examples of materials (macromolecules) internalized by receptor-mediated endocytosis...
- M6P receptor-bound, lysosomal proteins ‘escaped’ from TGN via secretory pathway
- Receptor complexes with bound cell signaling hormones (e.g., insulin) or growth factors (e.g., EGF)
- Iron (Fe3+ )-bound carrier protein ferrotransferrin recognized by transferrin receptor Cholesterol-containing, low-density lipoprotein (LDL) particle recognized by LDL receptor
37
AP2
- ***cytoplasmic protein serves as ‘linker’ during clathrin-coat vesicle assembly at pm***
- cytoplasmic-facing domain of receptor binds to AP2 adaptor ‘coat’ protein
- receptor-ligand-AP2 complex accumulates in clathrin-coated pit
38
Clathrin-coated pit
- ***specialized regions (indentations) of pm where receptor-ligand complexes are concentrated
and endocytic vesicles eventually form***
- inner (cytoplasmic) leaflet of pm at coated pit enriched in unique membrane phospholipids (membrane lipid microdomain)
39
Membrane lipid microdomain
- ***enriched in phosphatidylinositol (PI) (4,5) P 2 – serves as signal for recruiting AP2 with bound receptor-ligand into coated pit***
40
Phosphatidylinositol (4,5) P2
- ***serves as signal for recruiting AP2 with bound receptor-ligand into coated pit (found plentifully in the membrane lipid microdomain)***
- one of AP2s binding domains
41
Multivesicular late endosome: Multivesicular body
- ***contains numerous intralumenal vesicles
similar in size to transport vesicles, but opposite topology: MVB vesicles bud away from the cytoplasm (unlike COPI/II and clathrin vesicles - bud towards cytoplasm)***
- formed via inward budding of vesicles into late endosome interior
42
ESCRT machinery
- ***soluble (cytosolic) protein constituents recruited to MVB surface - mediate membrane ‘cargo’ protein selection and inward vesicle budding***
- endocytosed membrane proteins destined for degradation linked to mono-ubiquitin
- disassembly of ESCRT complex by Vps4 ATPase
43
Mono-ubquitination
- ***signal for recognition by ESCRT protein Hrs and subsequent entry (packaging) into newly-forming MVB
vesicle***
- Hrs also mono-ubiquitinated
44
Hrs
- ***Hrs recruits additional ESCRT proteins -- assemble to mediate inward budding and scission of
nascent vesicle into MVB lumen***
45
Vps4
- ***mediates disassembly of ESCRT complex***
46
HIV Gag protein
- ***HIV Gag protein functions similar to ESCRT Hrs***
