Lecture 11: Golgi and Lysosomes-Function and Trafficking Flashcards Preview

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Flashcards in Lecture 11: Golgi and Lysosomes-Function and Trafficking Deck (48):
1

Golgi complex

  • Ordered series of flatten membrane stacks called cisternae 
  • Usually consist of 4-6 cisterna 
  • Each of the Golgi cisterna have unique protein (and lipid) composition 
  • Stacks are often connected by tubules to form a continuous organelle 
  • Located in the perinuclear region (around the nucleus) close to the centrisome 
  • Localization is maintained by microtubules 

2

Model of the Golgi Complex

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3

Which stains can be used to indicate the different golgi compartments?

Trans face- Nucleoside diphosphate

Cis face- Osmium

TGN- Acid phosphatase

4

___ proteins cause coating with COPII in the golgi

Sec proteins

5

The ____ complex begins to build a coat 

Sec23/Sec24 

6

The ___ complex finishes the coat 

Sec13/31 

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Coat proteins also help sequester ____

cargo receptors

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In what 3 ways are cargo selected for inclusion in vesicles?

  • Export signals
  • Retention
  • Bulk flow

10

Export Signals

 Proteins to be transported have a export signal that allows selective packaging into transport vesicles

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Retention

  • Proteins have a mechanism to be excluded form transport vesicles 

• Chaperone binding 

• Kin Recognition 

12

Bulk flow

– Some proteins get packaged simply because they are in the right place at the right time 

13

_____ also participates in decision about entry into COPII transport vesicles and ER exit 

  • The ER quality control apparatus
  • Most of the time this is a good thing to prevent inappropriately folded protein or subunits of unassembled complexes from reaching the cell surface 
    • Large amounts (up 90%) of the T-cell receptor, acetylcholine receptor are degraded and never reach the cell surface

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In what case is the quality control machinery is too good?

– Cystic Fibrosis Transmembrane Regulator (CFTR) 

16

ER-derived transport vesicles fuse to form ____

vesicular tubular clusters (VTC)

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17

VTC’s form by ____ membrane fusion

homotypic

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18

What happens when ER resident proteins get transported out of the ER? 

They are actively retrieved! 

– Soluble residents 

• KDEL sequence and receptor 

– Membrane bound residents 

• KKXX motif 

19

How does the KDEL receptor know when to bind and when to release KDEL-containing proteins? 

  • The interaction between the KDEL tetrapeptide and the KDEL receptor is pH sensitive. 
    •  The relatively acidic pH of the Golgi compartment permits the association of the KDEL tetrapeptide with the KDEL receptor 
    • The more neutral pH of the ER allows release (and prevents binding) 

20

The KDEL receptor binds to escaped KDEL protein in the ____

cis Golgi

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ER-Golgi anterograde and retrograde traffic

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22

_____ function to anchor and localize transport gesicles

Golgins

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How do golgins do anchor and localize vesicles?

Through a rab interaction domain and a cytoskeletal interactor domain

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24

What are the two models of intra-golgi transport?

  1. Vesicle transport model
  2. Cisternal maturation model

25

Vesicle transport model

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Cisternal Maturation Model

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27

Biochemical functions of the Golgi 

• Glycosylation 

– Modification of existing Nlinked sugars 

– O-linked glycosylation 

– Production of proteoglycans 

• Protein sorting 

• Sulfation 

– Specific tyrosine residues in proteins

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Biochemical function of the cis golgi network

  • phopsphorylization of oligosaccharides on lysosomal proteins

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biochemical functions of cis cisterna

  • removal of Man

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Biochemical function of medial cisterna

  • removal of Man
  • addition of GlcNAc

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Biochemical functions of trans cisterna

  • addition of Gal
  • addition of NANA

32

Biochemical functions of trans golgi network

  • sulfation of tyrosines and carbohydrates

33

What is the purpose of protein glycosylation? 

• Aid in protein folding 

– ER quality control 

• Surface coating 

– Since animal cells do not have a cell wall, the extended surface coating by sugars provides come degree of protection from the extracellular environment 

• Specific interactions 

– Some sugars provide interaction surfaces for cell-cell recognition 

• Extracellular Matrix 

34

What's the signal for glycosylation?

 --Asn-X-Ser/Thr-- 

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35

Two main classes of N-linked glycans?

  1. Complex oligosaccharides (Gal and NANA)
  2. High-Mannose oligosaccharide (Man)

36

Order of sugar modifications?

  1. Glucoses removed by glucoxidases in ER
  2. Some Mannoses removed by mannosidases in both the ER and Golgi (to become High-mannose when has 6-Man)
  3. GlcNAc added by N-acetylglucosamine transferase I and Man further removed
  4. Step 3 repeats until 3 Man are connected each to a GlcNAc, Gal, and NANA 

37

Sugar modification diagram

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In Proteoglycan production (O-linked glycan) sugars are added....

in the golgi and as repeating disaccharides

39

O-linked glycans are very ____ while N-linked are very____

O= straight

N= highly branched

40

Lysosomes

• Primary degradative organelle 

– Degrades proteins, lipids and other cellular constituents taken in by endocytosis, phagocytosis, and autophagy 

• Other functions 

– Stores osmolytes 

– Stores nutrients as well as waste products 

• Heterogenous in size and function 

41

What's the hallmark of autophagy?

double membrane

42

Stages of autophagy?

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• Most lysosomal proteins (including the hydrolases) leave _____ and are diverted to the lysosome 

the secretory pathway

44

How are lysosomal proteins segregated from other secretory proteins? 

They contain a specific modification on their oligosaccharides - a phosphate group on the 6-position of a terminal mannose (M6P)

45

How is M6P added?

• Lysosomal proteins contain a “signal patch” that is seen by the enzyme N-acetylglucosamine phosphotransferase (GlcNAc) 

• This enzyme binds both the high mannosecontaining lysosomal protein to be modified and UDP-GlcNAc and catalyzes the transfer of GlcNAc phosphate to a terminal mannose residue 

• The GlcNAc sugar is removed by a glycosidase leaving the mannose-6-phosphate 

46

Inclusion-Cell (I-cell) disease is caused by a mutation in _____

GlcNAc phosphotransferase

47

Where does the Mannose-6 phosphate receptor (M6PR) reside?

Trans-golgi network

48

M6PR binding is ___ sensitive

pH, dissociates in acidic conditions of early endosome