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BIOC 341 > Lecture 11: Golgi and Lysosomes-Function and Trafficking > Flashcards

Lecture 11: Golgi and Lysosomes-Function and Trafficking Flashcards

1
Q

Golgi complex

A
  • 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
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2
Q

Model of the Golgi Complex

A
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3
Q

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

A

Trans face- Nucleoside diphosphate

Cis face- Osmium

TGN- Acid phosphatase

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4
Q

___ proteins cause coating with COPII in the golgi

A

Sec proteins

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5
Q

The ____ complex begins to build a coat

A

Sec23/Sec24

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6
Q

The ___ complex finishes the coat

A

Sec13/31

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7
Q

Coat proteins also help sequester ____

A

cargo receptors

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8
Q
A
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9
Q

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

A
  • Export signals
  • Retention
  • Bulk flow
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10
Q

Export Signals

A

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

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11
Q

Retention

A
  • Proteins have a mechanism to be excluded form transport vesicles
  • Chaperone binding
  • Kin Recognition
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12
Q

Bulk flow

A

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

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13
Q

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

A
  • 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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14
Q
A
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15
Q

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

A

– Cystic Fibrosis Transmembrane Regulator (CFTR)

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16
Q

ER-derived transport vesicles fuse to form ____

A

vesicular tubular clusters (VTC)

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17
Q

VTC’s form by ____ membrane fusion

A

homotypic

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18
Q

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

A

They are actively retrieved!

– Soluble residents

• KDEL sequence and receptor

– Membrane bound residents

• KKXX motif

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19
Q

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

A
  • 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)
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20
Q

The KDEL receptor binds to escaped KDEL protein in the ____

A

cis Golgi

21
Q

ER-Golgi anterograde and retrograde traffic

A
22
Q

_____ function to anchor and localize transport gesicles

A

Golgins

23
Q

How do golgins do anchor and localize vesicles?

A

Through a rab interaction domain and a cytoskeletal interactor domain

24
Q

What are the two models of intra-golgi transport?

A
  1. Vesicle transport model
  2. Cisternal maturation model
25
Q

Vesicle transport model

A
26
Q

Cisternal Maturation Model

A
27
Q

Biochemical functions of the Golgi

A

• Glycosylation

– Modification of existing Nlinked sugars

– O-linked glycosylation

– Production of proteoglycans

  • Protein sorting
  • Sulfation

– Specific tyrosine residues in proteins

28
Q

Biochemical function of the cis golgi network

A
  • phopsphorylization of oligosaccharides on lysosomal proteins
29
Q

biochemical functions of cis cisterna

A
  • removal of Man
30
Q

Biochemical function of medial cisterna

A
  • removal of Man
  • addition of GlcNAc
31
Q

Biochemical functions of trans cisterna

A
  • addition of Gal
  • addition of NANA
32
Q

Biochemical functions of trans golgi network

A
  • sulfation of tyrosines and carbohydrates
33
Q

What is the purpose of protein glycosylation?

A

• 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
Q

What’s the signal for glycosylation?

A

–Asn-X-Ser/Thr–

35
Q

Two main classes of N-linked glycans?

A
  1. Complex oligosaccharides (Gal and NANA)
  2. High-Mannose oligosaccharide (Man)
36
Q

Order of sugar modifications?

A
  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
Q

Sugar modification diagram

A
38
Q

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

A

in the golgi and as repeating disaccharides

39
Q

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

A

O= straight

N= highly branched

40
Q

Lysosomes

A

• 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
Q

What’s the hallmark of autophagy?

A

double membrane

42
Q

Stages of autophagy?

A
43
Q

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

A

the secretory pathway

44
Q

How are lysosomal proteins segregated from other secretory proteins?

A

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

45
Q

How is M6P added?

A
  • 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
Q

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

A

GlcNAc phosphotransferase

47
Q

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

A

Trans-golgi network

48
Q

M6PR binding is ___ sensitive

A

pH, dissociates in acidic conditions of early endosome

BIOC 341 (24 decks)

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