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MCB 2050 > Endomembrane System Part 2 - Lysosome > Flashcards

Endomembrane System Part 2 - Lysosome Flashcards

1
Q

what is the lysosome comparable to

A

the vacuole in plants

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2
Q

what is the lysosome

A

a digestive organelle that degrades all types of macromolecules

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3
Q

what is autophagy

A

degradation of larger cellular components/organelles

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4
Q

what does the lysosome play a key role in

A

autophagy

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5
Q

what does the lysosome contain

A

~60 different soluble acid hydrolase enzymes

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6
Q

when are soluble acid hydrolase enzymes active

A

only at low pH (about 4.6) of lysosome interior

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7
Q

how are resident lysosomal membrane proteins protected from degradation by acid hydrolase

A

lumen-facing carbohydrate groups

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8
Q

what happens to products of degradation

A

they are transported to cytoplasm to be reused by various biosynthetic/metabolic pathways

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9
Q

how is the low pH in lysosomal lumen maintained

A

membrane-bound ATPase proton pumps

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10
Q

what is the biosynthetic pathway

A

trafficking proteins to lysosomes

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11
Q

gist of biosynthetic pathway

A

lysosomal proteins synthesized and initially N-glycosylated in RER, then transported from ERES to golgi where they get further modified in cis-cisternae

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12
Q

what is M6P

A

signal patch - lysosomal targeting signal

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13
Q

fate of proteins without M6P

A

TGN–> secretory vesicles/granules–>pm/ECM

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14
Q

fate of proteins with M6P

A

TGN–>clathrin coated vesicle–>late endosome–>lysosome

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15
Q

what are late endosomes responsible for

A

uptake of plasma membrane proteins/receptors and extracellular materials/ligands
delivery to endosomes/lysosomes for internalization and/or degradation

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16
Q

what is the M6P receptor

A

integral transmembrane protein who’s luminal-facing domain binds to M6P groups on proteins

17
Q

what are AP1 and GGA adapter coat proteins

A

cytoplasmic proteins with multiple protein-protein binding domains

18
Q

what is Arf1 comparable to

A

Sar1 in COPII at ERES

19
Q

what is Arf1 involved with

A

initiation of COPI-vesicle assembly during retrograde transport from and within Golgi complex

20
Q

what does the binding of Arf1 to GTP cause

A

conformational change

21
Q

how does Arf1 undergo conformational change

A

exposed lipid anchor in Arf1-GTP directs it from cytoplasm to outer leaflet of TGN membrane

22
Q

what does one molecule of clathrin consist of

A

3 light chain polypeptides
3 heavy chain polypeptides

23
Q

what structure does clathrin form

A

3 legged: triskelion

24
Q

what do clathrin triskelions recruited from cytoplasm do

A

self assemble to form outer scaffolding of coat on growing vesicle

25
Q

what does clathrin assembly promote

A

curvature of TGN membrane

26
Q

what do individual clathrin triskelions initially self assemble to form

A

hexagons that lie flat on membrane cytosolic surface

27
Q

what do clathrin triskelions subsequentially self assemble to form

A

pentagons

28
Q

what serves as the mechanical driving force for membrane curvature

A

the triskelions transition from hexagons and pentagons

29
Q

what is dynamin

A

large soluble GTP-binding protein that mediates scission

30
Q

what does gamma-GTP incubation cause with dynamin ring

A

continued dynamin ring polymerization - results in long stalk with no scission of vesicle bud

31
Q

what is the pH in lumen of the late endosome

A

5-5.5

32
Q

what is a retorter transport vesicle

A

a recently discovered protein coat similar to COPI/II and clathrin

33
Q

what does the retromer complex coat mediate

A

membrane curvature and vesicle budding

34
Q

what does the retromer complex coat select

A

proper vesicle cargo

35
Q

what do retromer vesicles do when trafficking to plasma membrane

A

capture M6P bearing lysosomal proteins that escaped TGN via constitutive secretory pathway

36
Q

what are late endosomes a junction of

A

biosynthetic an endocytic pathways

MCB 2050 (11 decks)

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