Exam 3: RR (6)
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. What would you like to do?
- did what?
- i. Golgi invented new types of staining procedures to reveal the organization of nerve cells within the CNS
- 1. applied metallic stain to nerve cells from the cerebellum and discovered a darkly stained reticular network located near the nuclusà Golgi complex
- i. controversy: existed vs. artifact; resolved after it was clearly defined in unfixed, freeze-fractured cells
- i. consisting of flattened, disklike, membranous cisternae with dilated rims and associated vesicles and tubules
- ii. stacked cisternae that are curved
- 1. usually < 8
- 2. individual cells may contain from a few to several thousand distinct stacks
i. in mammals, they are __to form a single complex situated adjacent to the cell’s nucleus
ii. vesicles bud from a __of each __
iii. compartments arranged along an axis from the __(entry face closest to ER) to the __(exit face at opposite end)
- peripheral tubular domain
Cis face and function?
- 1. cis: composed of interconnected network of tubules referred to as the cis Golgi network (CGN)
- a. function: sorting station that distinguishes between proteins to be shipped back to the ER and those that are allowed to proceed to the next Golgi station
1. the bulk of the Golgi complex consists of a series of large, flattend __, which are divided into __, __ and __
__ of the organelle contains a distinct network of tubules and vesicles called the __
- cis, medial, and trans cisternae
- trans-most face
- trans Golgi network (TGN)
What is the TGN
a. the TGN is a sorting station where proteins are segregated into different types of vesicles heading either to the plasma membrane or to various intracellular destinations
i. the membranous elements of the Golgi complex are thought to be supported mechanically by a __ or scaffold composed of a variety of proteins, including members of the _, __, and __families—proteins that are also present as part of the __
- peripheral membrane skeleton
- spectrin, ankyrin, and actin
- plasma membrane skeleton
1. the Golgi scaffold may be physically linked with motor proteins that do what?
a. a separate group of fibrous proteins are thought to form a __” that plays a key role in the __
- direct the movement o vesicles and tubules entering and exiting the Golgi complex
- Golgi “matrix,
disassembly and reassembly of the Golgi complex during mitosis.
i. not __ from one end to the other
1. differences in __from cis to trans face= __
ii. pathway of newly synthesized membrane proteins, as well as secretory and lysosomal proteins?????
1. through __, proteins that were originally synthesized in the rough ER are sequentially modified in specific ways
a. stepwise __reactions
- uniform in composition
- processing plant
- leave the ER and enter the Golgi complex at its cis face and then pass across the stack to the trans face
a. Glycosylation in the Golgi Complex
i. Golgi plays a key role in the assembly of the carbohydrate component of __ and __
1. as newly synthesized soluble and membrane __pass through the __ and __ of the Golgi stack, most of the __ are also removed from the __, and other sugars are added sequentially by various __
- glycoproteins and glycolipids
- cis and medial cisternae
- mannose residues
- core oligosaccharides,
i. in the Golgi, the sequence of sugars incorporated into oligosaccharides is determined by what?
the spatial arrangement of the specific glycosyltransferases that come into contact with the newly synthesized protein as it moves through the Golgi stack
1. the enzyme __, which places a __ at the terminal position fo the chain in animal cells, is localized in the __ of the Golgi stack, as would be expected if newly synthesized glycoproteins were continually moving toward this part of the organelle
- sialic acid
- trans face
1. in contrast to the __events that occur in the ER, which assemble a __, the glycosylation steps in the Golgi complex can be quite varied, producing carbohydrate domains of remarkable __
a. unlike the__, whose synthesis begins in the ER, those attached to proteins by __ are assembled entirely within the Golgi complex
ii. Golgi is also the site of synthesis of most of a cell’s complex polysaccharides
- single core oligosaccharide
- sequence diversity
- N-linked oligosaccharides
Two views of movement: first?
- 1. Golgi were transient structures
- a. cisternae formed at cis face by fusion of membranous carriers from the ER and ERGIC and that each cistern physically moved from the cis to the trans end o fhte stack, changing in composition as it progressed: cisternal maturation model
Two views of movement: second?
- 1. Second: cisternae of Golgi remain in place as stable compartments
- a. vesicular transport model: cargo is shuttled through the Golgi stack, from the CGN to the TGN, in vesicles that bud from one membrane compartment and fuse with a neighboring compartment farther along the stack
i. each of the various Golgi cisternae of a stack has a distinct population of __
ii. large numbers of vesicles can be seen budding from__
1. discovery that __ were capable of __form one Golgi cistern and __with another Golgi cistern in vitroà hypothesis: ??
- resident enzymes
- transport vesicles
- inside the cell, cargo-bearing vesicles budded from cis cisternae and fused with cisternae situated at a more trans position in the stack
Why the cisternal maturation model the consensus?
1. it envisions a highly dynamic Golgi complex in which the major elements of the organelle, the cisternae are continually being formed at the cis face and dispersed at the trans face
a. according to this, the very existence of the Golgi complex itself depends on the __
i. when the formation of transport carriers from the ER is blocked either by treatment of cells with specific drugs or the use of temperature-sensitive mutants,what happens to the Golgi?
- continual influx of transport carriers from the ER and ERGIC
- the Golgi complex simply disappears
1. when the drugs are removed or the mutant cells are returned to the permissive temperature, the Golgi complex rapidly __
2. certain materials that are produced in the ER and travel through the Golgi can be shown to do what?
- reassembles as ER-to-Golgi transport is renewed
- remain within the Golgi cisternae and never appear within Golgi-associated transport vesicles
1. Assumption that transport vesicles always moved in a “__direction (cisàtrans)
a. evidence indicates that vesicles can move in __ (transàcis)
2. composition of an individual Golgi cistern can change over time—from one that contains __to one that contains __
- forward” (anterograde)
- backward (retrograde) direction
- early (cis) Golgi resident proteins
- late (trans) Golgi resident proteins
i. Newer version of cisternal matural model showing role for __, which have been clearly shown to bud from Golgi membranes
1. in this model, these transport vesicles don’t __, but __
- transport vesicles
- shuttle cargo in an anterograde direction
- carry resident Golgi enzymes in a retrograde direction
a. instead, it is the __ themselves that serve as the __
i. this model is supported by EMs, where frozen sections were treated with __that were linked to __ prior to examination in the EM
- Golgi cisternae
- primary anterograde Golgi carriers
- gold particles
1. after treatment, the molecules were within the __, not in vesicles, supporting the __ within maturing cisternae but not within small transport vesicles
ii. __ are found in both the cisternae and associated vesicles, which strongly support the __
- anterograde direction
- mannosidase II molecules
- retrograde idea
i. the __ explains how different Golgi cisternae in a stack can be unique
1. there is still much debate about the anterograde and retrograde ideas
cisternal maturation model
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