Mechanisms of Secretion and Exocytosis

Question 1

Exocytosis

Answer 1

process by which intracellular membrane bound container fuses with PM

Question 2

Consequences exocytosis

Answer 2

1. Container contents released into extracellular space

2. PM expands with membrane components supplied by container

Question 3

Cargo of exocytosis

Answer 3

1. Soluble lumen and membrane proteins (derived from secretory pathway)
2. Ions and sm molecules transported across membrane by specialized protein channels and transporter

Question 4

2 types exocytosis

Answer 4

constitutive and regulated

Question 5

constitutive exocytosis

Answer 5

after biogenesis transport carriers will travel to, dock, and fuse with PM without further signal input

Question 6

Regulated exocytosis

Answer 6

after biogenesis transport carriers only fuse to PM in response to signal

Question 7

Mammary alveoli

Answer 7

Example of constitutive exocytosis; can be manipulated to produce biological pharmaceuticals (use animals who are biologically engineered to produce certain pharmaceuticals in milk); better to do this way b/c cheaper and bc proteins need to fold correctly and this is correct mammalian environment

Question 8

Examples regulated exocytosis

Answer 8

Sperm and egg fusion (calcium regulation), neuronal exocytosis (neurotransmitter w/ neurosecretory vessel), insulin secretion (endocrine cells make insulin, released by exocytic release hormone); contact dependent (cytotoxic T cells, contacts target then endocytosis and releases content)

Question 9

paracrine signaling

Answer 9

signaling molecules released by cell only affect target cells in close proximity, conducting of electric impulses from 1 nerve cell to another via paracrine signaling

Question 10

Ca2+ signal and exocytosis

Answer 10

Rise in intracellular calcium leads to exocytic vesicles fusing with PM

Question 11

Regulated insulin secretion

Answer 11

1. Pancreatic endocrine beta cells respond to elevated B/G
2. Intracellular rise in ATP -> Closure ATP sensitive K+ channels
3. K+ channel closes depolarizing cell -> influx Ca2+ from voltage gated ion channel
4. rise intracellular Ca2+ -> insulin containing exocytic vesicles to fuse with PM

Question 12

Insulin uptake into cell

Answer 12

1. Insulin receptor on PM binds insulin

2. Signal causes relocalization of glucose receptors to PM boosting glucose uptake into cell

Question 13

bilayer fusion

Answer 13

SNARE proteins responsible for bilayer fusion during vesicle transport

Question 14

properties of SNARE proteins

Answer 14

1. LG protein family w/ compartment specific location
2. Membrane anchored (mostly TM proteins)
3. Large cytoplasmic domain w amphipathic helices
4. Ampipathic helices continuous w anchoring transmembrane domains
5. sufficient for membrane fusion when reconstituted in liposomes
6. complimentary sets on 2 membranes destined to fuse (v-SNARE and t-SNARE)
   * stabile associated with membranes**

Question 15

V-snares

Answer 15

on secretory vesicle membrane (synaptobrevin in case of neuronal exocytosis)

Question 16

T-snares

Answer 16

on target PM (SNAP-25 and syntaxin t-SNAREs of neuronal exocytosis)

Question 17

Molecular mechanism of SNARE protein action

Answer 17

very broadly, not tested on this
coiled-coil structure bc ampipathic alpha helices wrap around each other and form super helix with stable rigid superstructure

Question 18

Assembly of coiled-coil structure

Answer 18

(4 helix bundle) drives bilayer fusion with complimentary sets of SNARE protein on vesicles and target compartments; common feature SNARE complex formation at other stages of membrane fusion in secretory and endocytic system

Question 19

viral entry into cell

Answer 19

exploits endocytosis; goes through PM this way then into cytoplasm PH changes leads to conformational change and this is when it breaks out

Question 20

SNARE protein complex assembly

Answer 20

drives exocytosis; v-SNARE and t-SNARE complimentary; 4 helical bundles form synaptic vesicle exocytosis

Question 21

Enveloped viral mediated fusion vs SNARE mediated membrane fusion

Answer 21

Virus has to be both V snare and T snare and bring both elements together

Question 22

botulism toxin

Answer 22

SNARE protein synaptobrevin is target of botulinum toxin protease (botulism is a neurotoxin); pathogenic bacteria Clostridium botulinum present in soil; birds can ingest toxin or eat invert containing toxin; cycle develops in botulism outbreak when fly larvae feed on animal carcasses and ingest toxin, ducks can develop botulism from eating 3-4 maggots

Question 23

Toxins and SNARE proteins

Answer 23

other SNARE proteins are targets for other bactieral toxins (toxins are different proteases for different snare molecules)

Question 24

membranes of exocytic vesicles

Answer 24

SNARE proteins not only protein molecule on membrane of exocytic vesicles others also contribute

Question 25

contributions non snare proteins on membrane exocytic vesicle

Answer 25

1. participate in docking and fusion of exocytic vesicles
2. model organisms used to ID these proteins
3. many of these proteins regulate SNARE fx (ex NSF)
4. specialized transporters import small molecules and ions into exocytic vesicle lumen

Question 26

NSF

Answer 26

ATPase chaperone protein that assists other proteins achieve correct conformation (this -> unfolding SNARE -> conf change to disengage it from coiled-coil bundle so that it can do its job multiple times otherwise it would bind and since it binds V stabile it would stay there)

Question 27

Secretion of specialized secretory lysosome

Answer 27

vesicles fusing w PM during exocytosis usually Golgi derived but there are types specialized lysosomes in differentiated cells that undergo exocytosis

1. Hematopoietic cells such as granulate exocytosis of CTL
2. Melanosomes
3. Sperm acrosome

Question 28

Cargo specialized secretory lysosome

Answer 28

once such cargo is cytotoxic T cell which is contact dependent

Question 29

Lysosomes and exocytosis

Answer 29

regular lysosomes of all cells have capability to undergo regulated exocytosis under special conditions; acting in repair of ruptured cell when lg quantity PM needed for resealing

Question 30

Machinery used in lysosomal exocytosis

Answer 30

uses analogous molecular machinery of regulated exocytosis (ie SNARES and molecules that regulate SNARE machinery)