Endomembrane System Part 2 - Secretory Pathways

Question 1

2 secretory pathways responsible for transporting cargo from TGN to pm/extracellular space

Answer 1

constitutive secretion pathway
regulated secretion pathway

Question 2

gist of constitutive secretion pathway

Answer 2

materials are continuously transported via secretory vesicles from TGN to pm

Question 3

what occurs in constitutive secretion pathway when secretory vesicles reach pm

Answer 3

they fuse via Rabs and SNAREs and release lumenal soluble cargo outside cell

Question 4

what happens to vesicle membrane cargo components in constitutive secretion pathway

Answer 4

incorporated into plasma membrane

Question 5

what is considered the default secretion pathway

Answer 5

constitutive secretion

Question 6

what is the constitutive secretion pathway the pathway for

Answer 6

proteins not selectively sorted through biosynthetic pathway or regulated secretion

Question 7

what do materials at TGN get packaged into in regulated secretion pathway

Answer 7

secretory granules

Question 8

in regulated secretion, what occurs in response to cellular signal

Answer 8

granules stored in cytoplasm target to and fuse with pm and release their lumenal cargo outside cell

Question 9

what pathway operates in the opposite direction of secretory pathways

Answer 9

endocytic pathway

Question 10

gist of endocytic pathway

Answer 10

materials move into cell via gesticulation of pm and are either recycled back to pm or sorted to different intercellular destination

Question 11

what are the 2 main processes for internalization

Answer 11

phagocytosis
endocytosis

Question 12

gist of phagocytosis

Answer 12

uptake of large, particulate materials from extracellular space by specialized cells

Question 13

what do FC receptors signal

Answer 13

reassembly of actin microfilament network

Question 14

what are pseudopods

Answer 14

alterations in cytoskeleton that result in changes in shape of leukocyte-cell extentions

Question 15

what does phagosome-lysosome fusion get blocked by

Answer 15

Mycobacterium tuberculosis

Question 16

what are the 2 main endocytic pathway processes for internalization

Answer 16

bulk-phase endocytosis
receptor-mediated endocytosis

Question 17

what is another term for bulk-phase endocytosis

Answer 17

pinocytosis

Question 18

gist of bulk-phase endocytosis

Answer 18

non-specific uptake of extracellular fluids and plasma membrane proteins and lipids into small vesicles

Question 19

with bulk-phase endocytosis, how often does the pm recycle

Answer 19

20-90min

Question 20

gist of receptor mediated endocytosis

Answer 20

specific cell-surface (pm) receptor binds extracellular ligands and receptor-ligand complexes subsequently concentrated and internalized in clathrin coated transport vesicles

Question 21

examples of materials internalized by receptor mediated endocytosis

Answer 21

M6P receptor bound lysosomal proteins escaped from TGN
receptor complexes with cell signalling hormones or growth factors
ferrotransferrin
cholesterol containing LDL

Question 22

what is AP2 adaptor coat protein

Answer 22

cytoplasmic protein serves as linker during clathrin-coast vesicle assembly at pm

Question 23

what are clathrin coated pits

Answer 23

specialized regions of PM where receptor-ligand complexes are concentrated and endocytic vesicles eventually form

Question 24

what is the inner (cytoplasmic) leaflet of the plasma membrane at coated pit enriched in

Answer 24

unique membrane phospholipids

Question 25

what is the membrane lipid microdomain enriched in

Answer 25

phosphoatidylinositol (PI) (4,5) P2

Question 26

what does the PI (4,5) P2 membrane lipid microdomain serve as

Answer 26

signal for recruiting AP2 with bound receptor-ligand into coated pit

Question 27

what does AP2 have multiple of

Answer 27

binding domains

Question 28

what are the 3 binding domains in AP2

Answer 28

1. PI (4,5)P2 2. cytoplasmic domains of pm transmembrane receptors 3. clathrin

Question 29

what does AP2 form at cytoplasmic face of coated pit

Answer 29

inner layer of coat

Question 30

what is referred to as early endosome

Answer 30

nascent, uncoated endocytic vesicle

Question 31

what does degradation of endocytose membrane proteins involve

Answer 31

inward budding of vesicles into late endosome interior

Question 32

what does the inward budding of vesicles form

Answer 32

multivesicular late endosome or multivesicular body (MVB)

Question 33

what about MVB is unique

Answer 33

its morphology

Question 34

what does MVB contain numerous of

Answer 34

intralumenal vesicles

Question 35

comparison of MVB to transport vesicles

Answer 35

similar in size but opposite topology

Question 36

MVB topology

Answer 36

MVB vesicles bud away from the cytoplasm

Question 37

what do MVB vesicles selectively contain

Answer 37

membrane proteins destined for degradation in lysosome interior

Question 38

what mediates membrane cargo protein selection and inward vesicle budding

Answer 38

ESCRT machinery

Question 39

ESCRT: multi protein complex

Answer 39

soluble cytosolic protein constituents recruited to MVB surface

Question 40

what does multi-protein complex mediate

Answer 40

membrane cargo protein selection and inward vesicle budding

Question 41

ESCRT: what are endocytose membrane proteins destined for

Answer 41

degradation linked to mono-ubiquitin

Question 42

step 1 of ESCRT

Answer 42

signal for recognition by ESCRT protein Hrs and subsequent entry into newly-forming MVB

Question 43

what does Hrs recruit

Answer 43

addition ESCRT proteins

Question 44

what is step 2 of ESCRT

Answer 44

assemble to mediated inward budding and scission of nascent vesicle into MVB lumen

Question 45

what does Vps4 ATPase do

Answer 45

disassembles ESCRT complex

Question 46

step 3 of ESCRT

Answer 46

ESCRT components released into cytoplasm and recycled for additional rounds of MVB formation

Question 47

when ESCRT is hijacked by retroviruses what is similar

Answer 47

topology of vesicle budding at MVB is similar to enveloped retrovirus particle budding at plasma membrane in virus-infected cells

Question 48

What does HIV Gag protein function similarly to

Answer 48

ESCRT Hrs

Question 49

what is HIV Gag protein

Answer 49

major structural viral particle protein at pm and binds to and recruits (hijacks) ESCRT machinery to pm

Question 50

what does ESCRT mediate with retrovirus

Answer 50

budding and scission of nascent virus particle into extracellular space for subsequent infection of other cells