Ch 13 Pt 1 Flashcards by Amelia Harman

Endocytosis and Exocytosis

Cells continually adjust composition of their plasma membrane and internal compartments in response to need

Exocytosis - adds to membrane
endocytosis - removes some of membrane

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Transport vesicle contains ___ transports___

membrane components and soluble lumenal molecules (called cargo)
Transport vesicles bud from one compartment and fuse to another; selective process

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Two selectivity steps in vesicle transport

Captures right material
fuse to right membrane

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Organized routes of vesicular traffic

Secretory Pathway (red arrows)
Endocytic Pathway (green arrows)
Retrieval Pathways (blue arrows)

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Secretory Pathway

Red
leads outward from the ER to the Golgi apparatus and cell surface, with a side route leading to lysosomes

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Endocytic Pathway

green
leads inward from plasma membrane

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Retrieval Pathways

Blue
balance flow of membrane between compartments (opposite direction)

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Structure of Golgi
Consists of ___
each golgi stack typically consists of___

Consists of a collection of flattened, membrane-enclosed compartments called cisternae (stack of pancakes),
each golgi stack typically consists of 4-6 cisternae
Has cis side - incoming material
Trans side - vesicle bud off from

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In animal cells, tubular connections between corresponding cisternae link stacks. This forms

a single complex (near cell nucleus)

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Functions of the Golgi Apparatus

Transporting, modifying, and packaging proteins and lipids into vesicles for delivery to targeted destinations.

Glycoproteins formed

Golgi Vesicles come into the cis face from the ER and leave from the trans face to the plasma membrane or lysosomes.

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Functions of coated vesicles

Coat: 2 layered structure performs 2 functions:

Inner coat layer concentrates specific membrane proteins in patch, selects membrane molecules for transport (very specific to what captured)

Outer coat assembles into basketlike lattice, deforms the membrane patch and shapes the vesicle (Shape of vesicle, assembles to form shape)

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Three main types of coated vesicles

Clathrin coated -from PM and between endosomal and Golgi compartments
COPI coated - (Coat proteins)-from Golgi to ER
COPII coated (Coat proteins)- bud from ER

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Clathrin coated vesicles

clathrin subunit consists of ___ which assembles into ___ to ___

Clathrin (outer layer of coat)

Each clathrin subunit consists of triskelion (three legged structure)

Clathrin triskelions assemble into basketlike framework (ie hexagons) to form coated pits (buds) on cytosolic surface of membranes

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Adaptor proteins in clathrin coated vesicles

form a discrete inner layer of the coat (between clathrin cage and membrane)

Bind coat to membrane and trap cargo receptors (select for specific set of proteins) and package them into vesicles

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associate with PIP in membrane

AP2 - adapter proteins - associates with PIP in membrane - once bind- enhance/selective for cargo receptors

PIPs makes/identity tags for membranes (different kinds in different membranes)

PIP- phosphoglyceride - modified with phosphate groups

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to fuse with target membrane the vesicle must be

uncoated

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Dynamin

soluble cytoplasmic protein that assembles at the neck of each bud

regulates the timing of when vesicle buds by GTPase activity

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Coat complex, termed:

Coatomer or COP complex

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Non-clathrin coat observed on

isolated Golgi membranes and vesicles in transport assays.

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ARF proteins assemble

COPI and clathrin coats at Golgi

ARF proteins are GTPases

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Sar1 proteins assemble

COPII coats at ER membrane
(Sar1 proteins are GTPases)

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Formation of COPII coated vesicle

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Inactive SAR1-GDP binds to a Sar1-GEF (exchange) in ER, now SAR binds to GTP. GTP triggered conformational change in Sar1 , exposes an amphiphilic helix, which inserts into ER membrane. This initiates membrane bending
GTP-Sar1 binds to 2 adaptor proteins (Sec 23 and Sec 24): which form the inner coat
Complex of 2 additional coat proteins form the outer shell of coat (like clathrin, they can assemble on their own into cages)

Coat rectruitment GTPases in coat disassembly COPII

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Once vesicle pinches off, GTP hydrolysis releases Sar. Sealed coat is stabilized through interactions (ie binding to cargo receptors), phosphorylation step completes disassembly when vesicle docks at target membrane (kinase at the membrane)

Coat rectruitment GTPases in coat disassembly Clathrin and COPI

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shed coat soon after they pinch off (curvature of the membrane)
pip phospatase - removes phospate - detach membrane of pups - reduce affinity to coat

Rab is a ___ asspcates with ___ ___ distrabution

GTPases Associated with one or more membrane-enclosed organelle Selective distribution across membranes (ideal marker)

GDP-Rab

(inactive and bound to another protein: Rab-GDP dissociation inhibitor, GDI), protein soluble assocate with GDI - keeps soluble

GTP-Rab

(active and associated with membrane of organelle or transport vesicle)

Rabs and SNARES

Interactions between v-and t- SNARE : formation of

stable four helix bundle (Trans-SNARE complex) which overcomes the water barreror the trans complex is the most stable conformation - is spontaious - releases energy - used to remove water barror

Trans SNARE complex catalyzes

membrane fusion by using energy released from helices wrapped around each other

Formation of stock in snare mediated membrane fusion

When cytosolic leaflet is close enough lipids flow from stock - non cytosolic - come together - new bilayer - rupture - compleets fusion process

SNAREs pried apart before function again

NSF: N-ethylmaleimide-sensitive fusion protein (ATPase).

Proteins leave ER in COPII vesicles but ___ can get captured

resident er protines can get captured in vessilces

exit signals on soluble cargo protines attach to cargo recptor witch

also have exit signal

ER to Golgi Transport:Export from the ER Is the protein correctly folded and assembled with other subunits? then what happens

If no, then the denatured or unfolded, protein is degraded. **Problem with mutation in CFTR protein If still bound chaperones and is actively still undergoing folding, then protein remains in ER. If yes, then protein is exported to the cis-Golgi network.

Homotypic membrane fusion

vesicels fuse together same donor membrane each have a set of both snares (V+T) clusters, irrecular synapses

___ function as a retrieval pathway (bring back resident proteins, SNAREs, cargo receptors)

COPI coated vesicles As soon as vesicular tubular clusters form, they bud off transport vesicles of their own, which are COPI coated vesicles

KDEL

ER retrieval signal ER resident proteins with KDEL sequence selectively bind to KDEL receptor: cycles between Golgi and ER

KDEL receptor affinity for KDEL sequence

must differ in each compartment lower in ER Higher in golgi

How change KDEL's afinity for KEDL sequence

compartments in golgi are more acidic than ER (V type pump) change its affinity

___(vesicle)mediates transport from the ER to the cis Golgi network.

COPPI

___(vesicle) coat protein forms a three-legged structure called a triskelion.

Catherin

___ (vesicle) are pinched off from their donor compartment by dynamin

Clatherin

SAR-GTP regulates the assembly of this coated vesicle

COPII

These vesicles bring back ER resident proteins that have escaped to the Golgi

COPI

Which of the following vesicle(s) must shed their coat before membrane fusion?

ALL

Oligosaccharide Processing in Golgi Occurs in organized sequence in

the Golgi stack, with each cisternae containing a characteristic mix of processing enzymes enter cis, exit trans Golgi - site of processing and sorting (sugar modification is needed for)

Resident proteins of Golgi are

Membrane-Bound

Complex Oligosaccharides VS High Mannose Oligosaccharides

Endo H (Bacterial toxin that cleaves off sugar between 2 GlcNac sugars, if specific Mannose is present) EndoH cleavage site Important mannose being sensed by EndoH Endo H sensitive - high mannose Endo H resistant - complex

Purpose of Glycosylation

1. Promotes protein folding 2. More resistant to digestion by proteases 3. Cell adhesion (selectins) 4. Immune function: presence of sugar can modify protein’s antigenic properties 5. Regulatory role

Two theories of maturation

cisternal maturation and vesicle transport

Cisternal Maturation

Transport through the Golgi Apparatus cis becomes trans ( mature, more cargo with each cisterna) Backward movement how regulate enzymes (bring back enzimes to previous comparment) dynamic changing of golgi

Vesicle Transport Model

Golgi is static retorgrade - "resident enzymes" - need to bring back if excape

What would happen if a soluble secretory protein is genetically modified, with KDEL sequence added

it would go to the ER because KDEL has a ER retention signal

Ch 13 Pt 1 Flashcards

(54 cards)