Chapter 6: Golgi and Endosomes

Endosomes

Vesicle-bound materials are transported to a dynamic network of tubules and vesicles known collectively as _______

H+ ATPase

The fluid in the lumen of endosomes is acidified by a _______ in the membrane

Early Endosomes

Typically near the periphery of the cell; one of the classes of Endosomes

Late Endosomes

Typically further from the cell membrane; one of the classes of endosomes

Decrease; Rab; internal

Early endosomes progressively mature into late endosomes by the sequential _____ in pH, exchange of ____ GTPases, and a major change in the ______ morphology of the structures

Housekeeping receptors

Receptors responsible for the uptake of materials that will be used by the cell; we use on a day-to-day maintenance

Low

Housekeeping receptors dissociate in the ____ pH environment of the early sorting endosome and are recycled

ESCRT complexes

The vesiculation process of signaling receptors is orchestrated by a series of protein complexes known as ______

Multivesicular body (MVB)

Internal vesicles in the late endosome, cause it to be referred to as ______

Early endoscopes

The primary sorting compartment for internalized material

High; low

Early endosomes have a ____ surface to ___ volume ratio to allow for the accumulation of membrane components heading back to the PM

Microdomains

Specialized domains orchestrate membrane tabulation, invagination, and fusion by creating _____ within the same endosome

V; rotary; protons(H+);

__-type _____ ATPases pump _____ into the endosomes, progressively lowering the luminal pH along the endocytic pathway

pH

The _____ gradient controls where each cargo molecule dissociates

Transmembrane; late

MVBs form when sequestered _______ proteins get aggregated into membrane invaginations of the _____ endosome

Endosomal

MVBs pinch off and form small vesicles inside of the ______ lumen

Plasma membrane; exosomes

In some cells, the MVB may fuse with the ____ _____, releasing _____ into the extracellular fluid

Clathrin-mediated

The endosomal pathway is largely used by vesicles formed by ________ endocytosis

Trans Golgi Network (TGN)

Nonclathrin/noncaveolar endocytic structures deliver components to the _______

ER export sites (ERES)

Transport of newly synthesized proteins out of the ER takes place in specialized areas called _________

Vesicular Tubular Carriers (VTCs)

Vesicles and tubules detach from the ER and move to the Golgi as transport intermediates called _____

3 modes of transport out of the ER used by cargo molecules

Bulk flow(soluble luminal proteins); signal-mediated transport (via COPII); partitioning in the lipid bilayer

Sar1 GTPases

_____ initiates the formation of the ERES by assembling COPII coats that form coated buds and concentrate integral membrane proteins in the bud

SNARE

The _____ proteins allow vesicles and membrane tubules that bud from the ERES to fuse themselves to form a tubule cluster

Rab1 and Arf1

____ and ____ effectors help link newly formed vesicles to the cytoskeleton

Dynein

Molecular motor ___ helps detach VTCs and transports them to the Golgi

Cis-Golgi

VTCs fuse with membranes on the tubular __-Golgi network, releasing cargo proteins and lipids Into the Golgi

Carbohydrate

Function within the secretory membrane system: is a factory to synthesize the _______ chains of glycoproteins, proteoglycans, and polysaccharides

Protein

Function within the secretory membrane system: A ______-sorting station for delivery to many cellular destinations

Sphingomyelin

Function within the secretory membrane system: It synthesizes _______ and glycosphingolipids; these lipids associate with cholesterol and influence sorting

Microtubule Organizing Center (MTOC)

Ribbon-like structure adjacent to the nucleus and close to the centrosome

Cisternae

Golgi consists of flattened stacks of membrane ______ interconnected by a network of tubules and vesicles at the rims of the stacks

Microtubule

The stacks of Golgi are anchored to the ______ network that emanates from the MTOC

3 proposed mechanisms to explain transport of cargo through the Golgi

Vesicle transport, cisternal progression, and lipid partitioning mechanism

Golgi; cytosolic

Peripheral proteins (like GTPases and COPs) exchange constantly between the _____ membranes and _____ pools

Glycosyltransferases

Golgi enzymes that adds carbohydrates to a chain

Glycosidases

Golgi enzymes that takes off carbohydrates from a chain

Serines and threonines; glycosylation

Oligosaccharides can also be added to ____ and ____ in O-linked _______ to generate proteoglycans

Prohormone convertases

Some proteins, including peptide hormones made as large precursors, are cleaved into active fragments in the Golgi by ______ _______ (proteases)

Trans-Golgi network (TGN)

The exit pathway from the Golgi system; a system of vesicles and tubules similar to the VTC of the ER

Cell; lysosome; secretory

Cargoes that arrive at the TGN are destined for one of three places: the ____ membrane, endosome/______, or _____ granules

Kinesin

Vesicles are carried by _____ along microtubules to the plasma membrane from the TGN

Apical and basolateral; tight

Epithelia have functionally and compositionally distinct ____ and _____ membranes separated by ____ junctions that prevent diffusion btw the two membrane divisions

Carrier

Mechanism for polarized sorting of membrane components: selective packaging of proteins destined for each into distinct ____ vesicles at the TGN

Basolateral

_____ targeting inlvoes sorting signals in the cytoplasmic domain that contain YXXØ and [DE]XXXL[LI] motifs

Apical; lipid rafts

_____ targeting may involve partitioning into ____ ____ enriched with sphingomyelin and cholesterol formed in the TGN

AP and BL

Mechanism for polarized sorting of membrane components: Random distribution to the ___ and ___ membranes, followed by their selective retention and depletion, concentrating them in one place

Nonpolarized; polarized

Uniformly distributed proteins that preexisting on a ______ cell will redistribute in a _____ fashion in response to cell-cell contacts that initiate polarization

GPI; transcytosis

Proteins that associate with lipid rafts, including ____-anchored proteins, use _____ to reach the apical domain

Golgi

As the endosome mature and acidify, proteins are dissociated from MPRs and the MPR is recycled to the ____

LAMP (lysosomal-associated membrane proteins)

_____ family use these indirect and direct pathways to reach the lysosome

Secretory granules

Endocrine, exocrine, and neuronal cells use a third sorting pathway from the TGN to concentrate and package selected proteins in ____ ____

Proteins

Regulated secretory pathway is used to store and discharge secreted ____ in response to stimulation

Immature; mature

Secreted proteins bud from the TGB as _____ secretory granules (iSG) and _____ during storage (mSG)

Proteolytic; C-peptide

Pro insulin granules bud from the TGN and are cleaved by ____ enzymes to remove the __-peptide, which precipitates and leaves mature insulin

H+ and Zn2+

The combination of a ___-ATPase and a ____ transporter in the membrane of secretory granule vesicles helps aggregate and concentrate secretory proteins in secretory granules

Hydrolases; mannose; M-6-P

Enzymes in the cis-Golgi mark at least 50 different ______ for transport to lysosomes by phosphorylating the 6-hydroxyl of ____ to make ___

Kinds of hydrolases

Glycosidases, proteases, lipases, nucleases, and sulfatases

Lysosomal; receptors (MPRs); trans

The making of M-6-P is the sorting signal that directs _______ enzymes to M-6-P _____ in the ___-golgi for tarting to lysosomes

Clathrin

Sorting motifs in the cytoplasmic tails of MPRs target the receptor and bound lysosomal enzymes to ____-coated vesicles in the TGN for delivery to lysosomes

AP1

Interacts wit the cytoplasmic tail of MPR, Arf1-GTP, and PI(4)P on the TGN membrane to recruit clathrin to assemble a budding vesicle