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a. important that a cell be able to __
i. this is accomplished as the cell __
1. __ functions as a major __, directing proteins to various destinations
- distinguish among the various proteins it manufactures
- sorts proteins destined for different sites into different membrane-bound carriers
- trans Golgi network
- sorting station
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a. lysosomal proteins are synthesized on __ of the ER and carried to the __ along with other types of proteins
i. once in the Golgi cisternae, __ are specifically recognized by enzymes that catalyze the two-step addition of a __
1. thus, unlike other __sorted at the __, __ possess __, which act as __
- membrane-bound ribosomes
- Golgi complex
- soluble lysosomal enzymes
- phosphate group to certain mannose sugars of the N-linked carbohydrate chains
glycoproteins
- TGN
- lysosomal enzymes
- phosphorylated mannose residues
- sorting signals
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i. lysosomal enzymes carrying a __ are recognized and captured by __, which are integral membrane proteins that span the TGN membranes
mannose-6-phosphate signal
mannose-6-phosphate receptors
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a. lysosomal enzymes are transported from the __in __,w hich have a __ and an __
i. __ are escorted from the __by a family of adaptor proteins called __
- TGN
- clathrin-coated vesicles
- clathrin coated lattice
- inner coat of receptors
- lysosomal enzymes
- TGN
- GGAs
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a. GGAs
i. several __, each capable of what?
ii. outer ends bind to __, holding the __ onto the surface of the vesicles
- domains
- grasping a different protein involved in vesicle formation
- clathrin
- clatrhin scaffolding
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i. on the inner surface, the __ bind to a __ in the __tails of the __
1. the __then bind to a soluble enzyme within the __
ii. as a result of these interactiosn with __, the __in the __membrane and __ within the __lumen become concentrated into __
- GGA adaptors
- sorting signal
- cytosolic
- mannose-6-phosphate receptors (MPRs)
- MPRS
- vesicle lumen
- GGA adaptors
- MPRs
- TGN
- lysosomal enzymes
- TGN
- clathrin-coated vesicles
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1. production of __ at the TGN begins with the recruitment to the membrane of a small __, in this case __, which sets the stage for the __
a. Like Sar1, __extends a membrane-bending __that acts in conjunction with the __ to initiate formation of the __
- clathrin-coated vesicles
- GTP-binding protein
- Arf1
- binding of the other coat proteins
- Arf1
- alpha helix
- clathrin coat
- budding vesicle
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i. after the vesicle has budded from the TGN, the __ is lost and the __ proceeds to its destination, which may be an early __, __, or __
1. before reaching one of these organelles, the __dissociate from the __ and return to the TGN for another round of lysosomal enzyme transport
- clathrin coat
- uncoated vesicle
- endosomes, late endosomes, or plant vacuole
- MPRs
- lysosomal enzymes
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I. Sorting and Transport of Nonlysosomal proteins
a. membrane proteins destined for the __ and secretory materials destined for __ are also transported from the TGN
i. __ are produced as the __fragments into __and __of various size and shape
- plasma membrane
- export from the cell
- membranous carriers
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a. fits well with the __
i. proteins that are discharged from the cell by a process of __, like __, are thought to form selective aggregations that eventually become contained in large, densely packed __
- cisternal maturation model
- regulated secretion
- digestive enzymes
- secretory granules
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1. these aggregates are trapped as __ bud from the rims of the __and __
a. in some cells, long tubules are seen to be pulled out of the TGN by __ that operate along __, which are then split into several vesicles or granules by __
- immature secretory graneules
- trans Golgi cisternae and TGN
- motor proteins
- microtubular tracks
- membrane fission
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i. once they have departed from the TGN, the contents of the secretory granules become more __
1. eventually, the mature granules are stored in the __until their contents are released following __of the cell by a __or __
b. the targeted delivery of __ to the plasma membrane appears to be based largely on __ in the __ of the membrane proteins
- concentrated
- cytoplasm
- stimulation
- hormone
- nerve impulse
- integral proteins
- sorting signals
- cytoplasmic domains
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a. in __cells, membrane proteins destined to reside in the __protion of the plasma membrane contain different sorting signals from those destined for the __ or __ portion
i. these two groups of plasma membrane proteins are clustered into different TGN membrane domains and transported to the cell surface in __
- polarized
- apical
- lateral or basal portion
separate carriers
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1. plasma membrane proteins of __ cells, like fibroblasts and WBCs, may not require __
a. such proteins may simply be carried from the TGN to the cell surface in __of the __
- nonpolarized
- specila sorting signals
- vesicles
- constitutive secretory pathway
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